http://img.photobucket.com/albums/v349/mhborstad/Compound.jpg

Ok, this is an idea that I've been kicking around for a couple of years, but have never managed a chance to really dedicate myself to figuring it out. I'm releasing it to everyone here at slinging.org with one request - anyone who tries this please post here describing your results.

Slinging is limited by both the strength of the thrower and the speed that they can move their arm. Take away air friction, and it becomes a strength-only problem, with a coordination limit - the reason you can't just helicopter your way up through the speed of sound (speed of sound if there was air, of course ::)) You can trade strength against speed - a sling lets you move your arm slower with more force while moving the projectile quickly. A bow works by a different principal, storing energy, but this is also true of a sling with a longer windup - rather than just have the length of your arm to apply the accerating force over, we have the opportunity to add energy over a longer period of time.

The drawing above shows a sling-variant that might allow the thrower to "bank" energy that becomes available at the moment of release. The sling is compound - basically a sling attached to the end of a second sling. A mass heavier than the glans is attached to the end of the primary, retained sling, while the secondary sling holds the projectile. The pouch starts out in the slingers hand, and at the appropriate moment in the throw, it is released to swing through a larger path centered on the booster mass. The release is made in a conventional manner, but at the end of a significantly longer sling. The acceleration of the pouch and glans transfers kinetic energy from the booster mass, whose speed is reduced to near zero at the instant of release.

At least that's the way I picture it working... There are a couple major problems to be solved, as well as some tuning issues:

• Controlling the cords - For the design to work, the release cord must either pass through a fairlead at the booster weight, or it needs to terminate there. If you think of the primary as a staff-sling, you can see the potential for a mechanical auto-release. This might be a good idea , as we'll see. Alternatively, the release could be manually triggered, as in a standard sling.
  
• Dropping the pouch - this is both a timing issue as well as a physical problem. Once the pouch is released, the slinger has very little control over it's path and speed. It is also hard to drop the pouch without allowing slack to enter the cords and possibly dumping the ammo. This is only an issue for the first split second, but it might limit the throwing styles that can be used.
  
• Ratios etc - the ratio of booster mass to glans should be an important variable. It should be possible to calculate an optimum relationship (while we're at it it might be nice to see if this idea even has wings) but you want the booster heavy enough that it can store and transfer enough energy to move the secondary around efficiently. Too light is definitely a problem, while too heavy, aside from strength/injury concerns, is less clear. At least double.
  
• Timing - is *critical*. The secondary sling is supposed to be moving pretty quickly through it's sequence (the whole of which essentially takes place during the power-phase a regular sling throw). Coupled with that is the general lack of feedback, due to the booster mass. While it is definitely possible to release this sling normally, I suspect that something that times itself might be more reliable.
  

I've built a couple, but never had the space or the time to put them through their paces. I don't know if it can be made to work, but I'm pretty optimistic. The few test throws that I've managed without dumping the glans sound fast. The secondary cords whistle in a way that puts your neck hairs up. That's with a gentle lob. Given a big empty field, a weekend and a couple of interested slingers, I think there is a good chance of making this work. A release mechanism that seems like it might have potential is to make the booster relatively long, so that it is pulled in line with the retention cord. A pin and socket type release is added to the end (I made my booster around a piece of 20cm long pipe). If the hole goes all the way through as with a tube, you can use the same booster while trying a manual release.

A figure-8 seems the natural throw to use with this to me, as the motion fits the release sequence, and it is a relatively safe throw, with an easy to time windup.

CAUTION: more than the usual disclaimers apply here. Until we have this thing figured out, you are working with a highly experimental, tempermental sling, with a heavier than normal retained mass, complex timing issues, and a difficult release. Did I mention that I'm expecting this to be very very fast? I don't know what the failure modes are. If the pouch doesn't release, where does it go? Right back at your head? Kneecaps? What happens to the booster if the glans falls out early? You now have a rapidly moving object tied to your pinky (please don't use a pinky-only grip with this one). How wide does your downrange safe-arc of fire cover (I highly suggest 360 degrees)

Apart from all that, I'd like to hear what you think.

Matthias

Wow!!
Thats a lot of info, I'm having trouble understanding exactly how to sling a rock in this way, maybe a picture or a video would help.
Don A.

Very interesting.  It reminds me of something I can't quite dig out from the back of my mind, somethings to do with horology, maybe I've seen it in an old clock, can't remember sorry.  

I like the idea, I had a similar but far less efficient one for a mounted sling ( part of the physics of which your idea resembles, the leverage part ) The principle was to put a weight on the end of the releace cord and use it to jerk the pouch forward on casting.  So starting at the retention the sling components would be, stick with loop in end, flexable part of the retention, pocket, releace cord to stick with weight at stick end, second part of the releace cord fed through loop to hand.  The weight would be like a mace, with the folded sling on a wider orbit but trailing slightly behind.  At releace the weight would be releaced to move into it's larger orbit and the sling would rapidly unfold.  The glands would have what it normally does plus a bit of kick.  The concept being to turn some of the centripetal saved energy in the weight into forward motion of the pocket, the weight being releaced just prior to casting.  I only fiddled with it breifly and never got it to work.   You seem very close.  One suggestion I have is to go the full monty and go for a long mounted sling, the pole part being longer than both retention cord stages together.  This would give even more leverage and power but the main reason is safety. keeps the weight out of your way after the cast.  Running cords up tubes does seem best, though a fiddle to load, as it keeps the cords together. you may find however that the cords always stay to the same side of the tube when you throw which would allow you to split the back of the tube all the way along, or use hooks on the outside of a pole, which would be easier to load.  

If you did this though you would end up with a three stage sling, I'm not sure if the pole would compensate with regards to contollability.  If not then not such a good suggestion as I'm fairly sure from what you have said of testing with the prototype, the glands would exceed the speed of sound, a standard sling is only a hundred meters a second off or so and whip ends do it already.  Don't want to read "Fluke metiorite hit kills man, astronomers baffled by earth like rock.  Passers by heard a loud bang and found the man in a feild.  Unconfirmed reports say police removed a mysterious device from the scene of the tradgedy."

Hats off, Matthias.

Sounds amazing!  I'd love to try that design out.  Did you ever talk to Techstuf about it?  I got a feeling he would have something valuable to say.  

I can see the design work very well as a staff sling.  As a sling though, it would be very hard to control.

Matthias, great idea.

Is your diagram the result of a simulation? Reminds me of compound pendulums. If the release could be made to work it would surely scare a lot of people - not just the slinger ;D.

makes sense - pretty sure techstuff had a smiliar idea a while back.
Love the picture, though to be honest the written explanation made a lot more sense to me :-)

Well if you get a spare rig - I have plenty of big fields to test it in :-) Also going to be doing a video shoot after easter with an etruscan sling.

The main problem I envisage is that you'll have to hold both the pouch and relesae cord in the same hand, otherwise it'll just tangle you.

Certainly like to either try one or see one n action :-)

This sounds a bit like a Staff Sling, which boosts performance by giving more leverage.

The compound sling uses a booster mass to get more power, but I fear that the energy required to move the booster mass will slow down the entire sling, effecitvely eating up all extra power. The ideal sling should be light so that no energy is wasted for getting the sling itself moving.

Not so adaxl the enrgy you put into the booster mass is converted directly into the missile via the longer cord.
What it should allow you to do (if correctly made and working) is to put a lot more strength into the throw itself.
The heavier the missie in a normal sling the harder you can pull against it without straining your own muscles (it's like throwing a punch and missing, the hader you punch the more you hurt yourself when you miss).
The problem with a conventional sling is that sure you can use heavier ammo and up to a point you will get more distance. But at a certain weight your own strength will start to tell against you and the velocity will drop - even if you are putting more effort into the throw.
With this method you can put a lot of effort into a fairly slow throw which is then directly converted into a much faster throw with a lighter missile.

If it helps, think of it as gearing. High gearing on a bike lets you push really hard and pedal slowly but the wheels go round faster than low gearing where you pedal faster but with less effort and the wheels go round proportionally slower.

Matthias

It is clear that your compound sling uses a slack cord to supplant a rigid or semi-rigid rod akin to fishing tackle. Your concept might be developed and tested using a smallish treb setup, this can be a  much safer, consistent and rewarding way to experiment.

For a combination ballast weight/release, a battery pack and solenoid can be triggered by a relax thumb button. Of course the testing treb needs some sort of adjustable auto release. Compare the results from this new treb setup with same treb using the usual release cord.

Tom  

Bravo aardvark! You're officially promoted to associate question-fielding guy on this one.

I know it looks like a staff sling, or a treb, in that it has two parts and the motions are similar, but it's a quite different beast. The goal is to store energy in the booster (as much as possible) that can be released into the projectile in the final phase of throw. The booster itself essentially comes to a complete stop as the pouch is released - no loss of kinetic energy. Let's say I can throw a 300g rock just about as far as a 100g one, or a 50g (I'm speed limited, not strength). My speed at release is around 50m/s. The energies transferred to the rocks are 375J, 125J and 62.5J respectively. IF we could manage an efficient transfer of energy stored in a 300g booster, it might be possible to put those 375 Joules into the 50g projectile - 122m/s. _That_ is a very very fast throw. A golfball that normally goes 150m could hit 330...

http://img.photobucket.com/albums/v349/mhborstad/CompoundSim.jpg

Tech and I talked about it privately a bit a few years ago. There are a limited number of ways to get more power into a sling - he already has the length and aerodynamics covered :)

A couple of points raised:

re. the tube. This sling cries out for captive cords. If trying for a conventional release I'd allow maybe 6 inches of slack in the secondary before it caught itself. a knot or bead on the primary retention cord should be enough to handle this.

Rigid links. It's important that the "joint" at the wrist be flexible. Unlike a staff sling, we aren't levering this one into position, and the rotation about the hand is actually slowing during the final phase of launch. It is also desirable to concentrate as much mass as possible in the booster (and projectile) - this is the conventional sling argument that ADAXL raised. I think you could probably use a rigid link in there though, maybe witha  short piece of cord attached to a handle to give some more freedom of motion. Stick? Carbon tubing? A rigid or semi rigid link should simplify the release a little if using an automatic system. I think It's doable without going all high-tech though...

Two handedness. Yessss... It is a little tricky, but it seems to work ok. If using a "staff sling" secondary release you are back to only one thing to drop, and one timing problem (apart from intial setup)

I think that some of the more advanced treb simulators might be able to make a decent go of this, but the tip path isn't "standard" treb, nor is the weight distribution. Unless someone knows of one that is really flexible, it's probably easier to sort it out from scratch. The other option is to use one of the dynamics packages that are out there. Any engineering students should have access, and trials are available on the web. One day I might get to it, but it's a bit too much like my normal work...

Thanks for the comments on the drawing. I really like the sort of crazy nested epicyclic look to it - a lot like an orrery. Interesting the difference between the visual and verbal understanding!

Matthias

TechStuf does indeed have a technique where he holds the cords and pouch in the same hand.  This is his around-the-elbow technique.  You need a sling long enough to loop around your elbow and back up to your hand.  Start your cast with your arm bent (so the sling cords are secure around your elbow), hand at about face level.  Flip the pouch out of your palm and forward, and draw your hand back to where it started.  When the pouch reaches the bottom of its swing, flip your hand out again and release.  The sling will be accelerated around your arm and back up, for an overhand release.

Matthias, I've been looking at your drawing and trying to make sense of it.  The spiral curves for the pouch and for the booster mass, are fairly clear.  The curve coming in from the left, looping around itself and passing off to the right -- that has me puzzled.  Does that line represent your hand position, as you do a figure-8 with a step forward?

And where can I find that Slinging.org projectile motion calculator?

Right - hand motion. Only the last part of the path (from about the bottom of the little loop onward) relates to the steps shown, the incoming paths are just for show (although they should be pretty accurate). The paths and positions aren't taken from a simulation, or traced from video or anything, so there is a bit of artistic license. We'll have to put leds or reflectors on Tint one day and see if we can do some long-exposure-time photography to see how close I got!

The sim is another project started but not finished... :-/ I never got enough data to validate the results, and the interface is a little obtuse as it stands, but it is fun to play around with. It allows for spherical or ellipsoid ammo, and interpolates the Achenbach data to give an approximation of boudary-layer effects. Drag for ellipses asumes that they magically orient themselves tangent to the flightpath, instead of maintaining attitude.

Using it is pretty straightforward. Clicking on the display area clears and resets it (and draws the grid). Checking "show analysis" displays speed, drag and drag coefficient in addition to the tragectory. The curves implemented in the compiled copy are step-dicontinuous at transition, and constant at low Re. The drag values read from the top down.

I'm attaching a copy, zipped for anyone who wants to try. Windows only I'm afraid.

Matthias

---

Some years ago Matthias mentoned he was working on a compound sling. He interested me in it and I was thinking about it a while. I had a few ideas but never tried them out in practice. Anyway the question is so much interesting.

Matthias, your idea is great (not to say about the drawing) but I have some doubts regarding your solution. They are just my guesses and I might be wrong.

First one I'm not convinced about a superiority of the mentioned compoud sling over a good staff sling. I mean it made of a light springy carbon rode or so (let say with the "booster" mass on its end - it is another question for discussion). I'm rather prone to agree with ADAXL in this point. I would even say that the staff sling should work much better because it additionally can be controlled by the palm (either accelerated or slowed down) and the springy rod is able to accumulate an exess energy that can be released/given back in the last stage of the throw, when the body is not able to accelerate the hand more.

The second, in my opinion, big problem is the unprofitable angle between the cords just when the pouch is released from the palm. As a result the tension of the cords between the masses will be lost. Too bad for efficient slinging. It was mentioned though.

I'm also not sure if the booster mass stops completely and as a result transer the energy to the projectile. I'm not saying it is impossible, but it isn't very likely and predictable, because it depends on a lot of factors, similary like in mentioned by wanderer compound pendulum. That one made of two masses is enough crazy.

Matthias, sorry for my scepticism. I will try to add some of my ideas to yours, but first have to make some sketches.

Jurek

Please guys, tell me if I'm not clear.

Matthais,

I really like your idea, and frankly the innovative side of slinging is what I find more interesting. I see what you mean about it not being similar to a staff sling, in that most of the force on the projectile comes from the energy stored in the booster mass. From what I understood this means that if the mass of the booster is large enough, relative to the projectile, even a fairly slow swing will still send out the ammo at an impressive rate.

What if your booster mass, was actually a staff with a large weight at the end. From the picture below what you see then is….A small retention loop and cord attached to one end of the staff…The release cord and red pouch attached to the weighted end of the staff

So essentially it would look like you were swinging a triangle around. My guess is the more sections you have like this the more of a whip like action that you can get, am I right?

Shihab

---

Great to have your input Jurek! Always highly valued. Welcome shabundi as well. I'm a born skeptic - maybe we should start a new order: Sphendonetes Skeptikoi. I'm not sure that it can be made to work either, but I do think that the principles are sound.

I'm sure that a well made staff sling could produce a significant ammount of power, but the machanism is different, unless we start talking about very lightweight materials. Likewise, it turns out that yu can't use most treb simulators to play around with as they work off of the momentum of the arm and counterweight. The moving mass with a human slinger is quite low - alomst all of the energy input is force. With an elastic staff, you're adding another energy storage mechanism, and liek this one it would have to be tuned to the mechanics of the throw. I have no doubt that it would work either.

The angle problem is a very real one. I have managed throws like this though - in one of my earlier posts I think I mentioned that a captive pouch like Techstuf's star might be a big benefit. The problem can be lessened with a handle, or "mini staff" to give some space between the primary and secondary cords at the hand. The paths taken are relatively complex, but there seems to be a window in a fig-8 where the booster is moving fast enough and the hand is reversing directions. No one said this would be easy! ;D

The booster ends up moving pretty slowly at the time of release. Length of cords, weight ratio etc all factor in, but with no mass in the cords you can come very close. Here is a bodged simulation (and I said I wasn't going to do this... >:() showing a simple setup. This one is not optimised for energy transfer - with different initial conditions it was possible to stop the booster. I have no idea if that is an efficient thing to do with a human thrower. A double pendulum becomes chaotic very quickly, but the first swing or two are very predictable - just like a trebuchet?

http://img.photobucket.com/albums/v349/mhborstad/CompoundPlot.jpg

This was done with a program call "Working Model 2D" for which a free trial (no saves) is available. Slings aren't easy to simulate though - the hand motion is very much not a simple arc, as here, and the initial conditions are tricky to set up. A halfways ok start is to only simulate the final part of the throw, and give the components initial velocities to compensate. Even doing that, a four-bar linkage or similar would allow a better representation of the cast. Maybe cams? If you were really keen, you could do a pretty nice job, even releasing the projectile...

Matthias

Oh, I forgot to mention that the velocities shown in the plot exhibit the dip in speed of the booster and rapid acceleration of the glans. The speeds at release were 30 and 140m/s respectively using a 200g booster and 50g glans. Less mass transferred a higher percentage of available energy, but resulted in less speed, while higher masses seemed to reduce speed (slowly) The "muscles" driving this thing are nowhere near matched with a human though. I suspect that even the strongest of us would start to have trouble with 1kg boosters...

Matthias

I love this idea truly. I am just really confused about the goal. Please correct me if I'm wrong. You want to build up power in the sling then at the point of release have that power transfer to the projectile. This would give you more umpf! behind a lighter object. The power generated by the heavier weght is used as an extra kick while the weight itself never leaves the sling. This however does not prevent you from swinging the sling because you still have generate the initial power.

I'm sorry if thats all wrong, my reading comprehension not so good. I have toyed with weighted pouches. I have taken weights and attached them to the underside of pouches. I set them up so they hung on a cord in the exact center of the pouch abou two to three inches long. Looked like decorations. I found this to help a lot with lighter stones. The weights help to open the pouch quicker too. I think because the weights are on the outside, when you let go the pouch rips open. My main reason for adding the weights was to make the sling a useable weapon even without ammo.

Just finished the sketch of one of my mentioned ideas. That one seems to me be the best of them. I believe that solution is relatively simple to realisation and give a chanse to eliminate some discussed before problems. It also should give an additional profits. Sorry, there are too late hours to describe it more exactly, but I believe the sketch gives the idea clearly. Of course, the masses, all lenghts require to be adjusted in practice.

Warning: the compound sling, if not adjusted propely can be very dangerous for the slinger.

http://www.kajakowe.com.pl/sling/compound-sling.png
http://i0.simplest-image-hosting.net/picture/compound-sling.png

Jurek


_{Edit: Corrected the broken link to the picture.}

NOTE: I started this post, then drew the picture, then posted it, and only then did I see Yurek's post.  His drawing is better, because he shows how the sling is used.

Dork, after reading what you wrote, I do not think you got Matthias's idea.  He has a two-part sling.  If I built one of these (which I will probably do, so if all of a sudden I disappear from here you will know I killed myself with the monster) -- anyway, my version of this design would look something like the attached sketch.  I would hold the cords in my hand, and also hold the pouch and ammo in the same hand.  Then I wind up like I was going to sling the booster weight, but at just the right time I let go of the pouch and it swings out and up and the ammo flies off into the sunset.

Of course, the more probable result is that the cords tangle and I bash my own head in with the booster weight.

I think it should be mentioned that THIS IS AN ADVANCED SLINGING PROJECT AND SHOULD NOT BE ATTEMPTED BY BEGINNERS! (Good grief, so what I am explaining it for?  We are all crazy around here! Excuse me, I have to go build a sling...)

---

Jurek,

This whole idea reminds me of a roller-skating maneuver called the "slingshot".  One skater approaches another from behind, then they link hands and the skater in front pulls hard to swing the approaching skater past him.  The one originally in front is now behind and moving much slower, and the one who originally was behind is now in front and moving twice as fast!

Your design has the booster mass sliding or rolling down the cord, until it triggers the release?  That is even more wild than what Matthias was suggesting!  Would the moving booster mass, slow down the swing and assist the momentum transfer?

Alright! Here's hoping that Dale comes back and lets us know that a. he's ok and b. he managed to test the sling. Dale's drawing is basically the "manual release" option. The problems I had were (somehwat predictably) the timing (fast fast fast), holding three things at once, and slack in the secondary. I'm sure that there is a neat wrist-flick trick to solve the last problem - how many tries does it take the average slinger to figure a figure-8? This won't necessarily come easy! If it could be made to work it is by far the most attractive option to me personally - the purist approach.

A sliding release... I'll have to think about that one (resisting urge to put one into the simulator) At first glance, I don't think that it will give you enough time for the pouch to come around. It might also be pretty hard on your hand if it slid any distance (no pinky loops, remember) The _good_ news is that it might just put the booster out of danger range, allowing you to ground out a failed throw!

I'm glad we've had a healthy ratio of WARNINGS AND DISCLAIMERS in this thread. It might be that these things are puppy dogs, but the odds aren't good until we figure out some of the kinks...

I don't know where all of this head-bashing fear is coming from ;D I'll offer odds on left-leg charleyhorse followed by kneecaps, and of course the general groinal area...

Matthias

dork - your descripition is pretty much on, but the power boost in the compound comes from the motions that two connected slings work through. Weighting a standard sling might provide other benefits (accuracy, light ammo, loud noises) but it can't accelerate the pouch the way this one is supposed to.

shabundi wrote on Mar 25^th, 2007 at 6:50pm:

So essentially it would look like you were swinging a triangle around. My guess is the more sections you have like this the more of a whip like action that you can get, am I right?

Indeed. Ever since the whip-sling I've been trying to figure out a way to use the whip principle to launch a projectile. The compound is a slightly parallel design. Baby steps ;D

There is no way you are ever going to get the release timing right, if the pouch is anywhere near Mach 1.0!!  You are going to have to perfect the automatic release.

Whaaaa....? You're back with no report?  >: (I never said Mach 1, just respectably fast! If you think about what is going on, the whole secondary sling winds-up and releases in the same amount of time that the final snap usually takes. The release point is going to be the same (sling more or less directly overhead) and you should have decent feedback. Maybe? Maybe not. Automatic certainly seems to be a requirement as you go faster and faster.

I might as well jump in here.

I think the problem of timing and dealing with the release of multiple parts of the sling (release of the projectile restraint and release of the projectile from the sling) could be solved by an intelligent release mechanism.

I'm thinking of a pistol grip like device that has two catches on it.  You could have two separate buttons on it (I'm thinking a trigger to release the projectile from the sling and a thumb button to release the projectile portion of the sling).

You would then have a sequence something like:

1.  Start Swing
2.  Swing
3.  Thumb Release
4.  Continue Swing
5.  Trigger Release
6.  Projectile Launched
7.  Duck because the booster weight is going to smash you in the face.

It just seems really hard to pull this off by manually releasing these sequentially.

Not one to hijack a thread I just thought of throwing this out there.  I was inspired a few weeks ago about making a 'rubber' sling.  Remember those sticky rubber hands you had when you were a kid?  Yeah the ones that would melt if you left them in the car too long?  You could really get those things moving back and forth.  Well, I think designing a sling that has an elastic snap to it could add additional punch to the sling.  The sling would be swun in an eliptical pattern and the projectile launched while the the sling is snapping back into shape.  I have thought long and hard about what materials to use, but the only things I really come up with could be difficult to shape into a sling (the gel from inside computer arm rests come to mind, I saw a video once of a 1 ft long gel pad interior being swung back and forth and deforming approximately 15+ ft and snapping with great force).  Sorry for the side track.

I was way off on my thoughts. Now I get it. Be careful and good luck

I believe that the best solution for the issue of timed secondary (or final) release, is to simply not have one at all. This is one advantage to Yurek’s design, since you do not need to attempt to time a second release. I.e. once the initial pouch is released the booster mass will automatically trigger the final release of the ammo.

I believe one way to do that for matthais’s design, is incorporating the concept similar to what was proposed in the innovators nook…
http://slinging.org/forum/YaBB.pl?num=1079645737

The way that would be done is as follows bellow… for simplicity’s sake, imagine that the booster mass has a flat head, (and I apologize for the horrible diagram, but it was the best I could do)…

Basically, the release cords are longer then the retention cords. However, because the release cords are attached to the corner furthest away when the pouch is in your hand, the ammo is balanced in the pouch. But once the pouch is released and as soon as it reaches a point directly on top of the booster mass, the ammo will slide out from the side of the release cords.

Shihab

---

Oooo that's pretty sneaky shabundi! People have a tendency to get trapped into thinking that the release point has to be at the proximal end.

I am not sure it can be done either, FunSlinger.  But Matthias and Jurek have talked about it quite a bit and both think it might work.  I am game to try!  But mine is going to use something like a tennis ball for the booster weight, and maybe a squash ball for the ammo.  I am NOT risking my skull, or kneecaps, or potential descendants, on the chance that this will work first time.  I figure I am going to get tangled up in the rig quite a few times before I know if it is workable or not.

Oh, the desired goal?  Sheer raw SPEED!  If this gadget works, it is going to release at twice the velocity of a standard sling, maybe even more.  The Guinness world record is within my grasp! (assuming they can be talked into accepting it as a "sling", and Engvall convinced them that a metal dart was a "stone" so I have a fair chance).  Of course, I will have to get my rig working before Jurek gets his working, or I've got NO chance of making the record book. ;)

Ah ha finally a bit I can answer again lol
Forget the maths and the mechanics - don't have the inclination to tackle those, but I do actually understand the principle involved and for me jureks drawing makes things perfectly clear. And I do know about the physiology :-)

Funslinger The main reason we get sore joints when attempting to sling missiles - literally - out of sight,  is that we are moving our joints as fast as we can to transfer that speed into the sling. And to a certain extent even with a reasonable weight missile we're still putting in a lot more effort than can be efficiently translated into the missile (we're back to the punching and missing again).

This method relies on the slower application of force. It's like picking something fairly light up from the ground and doing so as fast as you can. Very easy to bugger your back up. If you pick something much heavier up with a more measured lift, your body will be working more efficiently and less likely to cause problems.

This compound sling works on the same principle. You are expending the same amount of energy, but in a more controlled and efficient manner.
Also you are using a much longer release cord - so effectively, if it works, you can sling with a 6 foot sling while retainng the velocity that you can manually impart to a 3 foot sling.

The impact on the slingers body should be less because your muscles are working more in harmony and with greater efficiency.   :-)

I do have to say matthias that yureks design does look a lot more elegant than yours sounds ;-)

Jurek,

I love your design, it's fantastic. As the booster weight moves further along the sling during release, it reduces the secondary sling radius, which in turn should accelerate the glande even more.

I haven't done the math, but it seems to me like the timing of the two releases would depend not just on sling lengths, but also on the ratio of the booster mass to the pouch+glande mass. It would be great if, for a known booster mass, the sling would have a series of markings such that for any given glande mass you could use a marking to compensate for the mass effects.

Reading this before work, I don't have time to build such a sling right now. But I did find an old toy, astrojax, to experiment with. It turns out the astrojax is a poor sling model. But it did give me this idea, which some creative slinger might incorporate somehow:

In the diagram below, string is black, rigid sticks are red. The booster weight, blue, would be a flared tube just wide enough for one string and one stick. As the booster weight slides down the retention cord, it also slides down the rigid release tip, until the tip is released. Another stick, or a large knot, can prevent the booster weight from sliding all the way to the pouch.

---

Dale,

I definitely agree with using safer objects for ammo and boosters. I would probably go as for as initially having a ping-pong balls for ammo instead of a squash balls since they can still pack quite a sting.

Funslinger,

Curious-Aardvark has explained the concept perfectly with respect to how much stress it might put on the body. I’m willing to wager that if matthais’s design works, that it can probably be modified to the point where the slingers can comfortably rotate a relatively slow but very heavy sling (maybe 2kgs in total), which ends up releasing a small projectile at an extremely high speed!

This still sounds dangerous I’m sure, but I wonder what people thought of the first guy that came up with the sling concept!

Pancaker

I think having a stick for the booster to slide on is very ingenious. I also imagine that there is supposed to be a release cord from you hand attached to the booster mass, but you haven’t shown it, right?

Honestly however, I believe that Yureks design might not work as well…Please take this as constructive criticism because I do not mean anything else by it. First in simply trying to imagine the scenario, it would seem to me that the ratio of the booster mass to the ammo must be much higher then in Mathais’s design. The reason being as Pancaker mentioned is the phenomenon of the ammo accelerating even more (therefore having more force) as the booster mass shortens the turning radius of the projectile.  If the booster mass isn’t large enough, then it might not travel down as smoothly.

Basically it this issue of a mass sliding down the string that is getting to me, cause I can just imagine the type of wear put on that portion of the sling. I guess it is imperative that the booster mass and sling, be of some kind of smooth material, that would minimize on friction.

Matthais

I’m very excited about the potential of your design, and I really look forward to hearing about results for any who are able to actually try it out. (Pictures would always be great!)

Shabundi

I thought a bit about Yurek's design and how to implement it. I think I have found a way to improve it. When the weight slides along the cord before it triggers the release I think it is very hard to get this done consistently. My proposal has an other cord with a nail at its end going from the retention cord to the release cord. When the sling straightens the nail gets pulled out and the pouch is released. This way I think you can get a fairly consistent release.

However I am not going to try this (yet). I still need to get the release of the basic sling right...

---

Hey that's not bad Dravonk... You don't need or want the moving booster with that one, but it should be a relatively failsafe automatic trigger.

On the sliding weights. It's easy to confuse angular velocity with speed. Shortening the radius of a spinning sling does speed up the rotation, but the projectile is still moving the same speed - all you've done is made it harder to judge the moment of release. Conservation of energy and all.

FunSlinger - I agree that the figure-8 is one of the more forgiving throws, particularily with a long enough sling. I guess the question is what weight of projectile with a standard sling allows you to put in the most energy. I guess if we had a better measurement of speed (or a working ballistic pendulum) we could plot a curve, but just based on range, I think there is probably a maximum for most people that occurs somewhere above the size of stone we normally sling. 3oz (85g) seems about right to me as well for a standard projectile, but I can throw heavier ones relatively comfortably. More importantly, I'm not able to throw say a 1oz glans with anywhere near the same power. Use the energy you put into the 3-4oz rock to fire the 1oz one, and there might be some potential (for speed/range)

On tennis/ping-pong/squash balls. There's a bit of a hitch... The higher speeds mean that air drag becomes a bigger problem, and the sling may start to lag beyond what is acceptable. The effective sling length is greater as well, although the booster helps out there if it does it's job. Maybe tennis ball ammo... So long as the sling is a reasonable length, it mostly just goes into the ground, irrespective of my own dire warnings. Follow through with your throw.

Matthias

Matthias wrote on Mar 27^th, 2007 at 1:42pm:

Hey that's not bad Dravonk... You don't need or want the moving booster with that one, but it should be a relatively failsafe automatic trigger.

Ah yes, I didn't write that clearly. This trigger method is supposed to be used instead of the moving weight. So in my concept the weight is already fixed, I just didn't say so. ;-)

I still don't see how the energy of the weight is put into the projectile, but I have to admit that my physics concerning connecting pendulums is not in the best shape currently. Hmm...if I remember correctly you can connect weights and send a wave over them...so it will probably work. Whoever builds and uses something like that, please give us a video! :-)

lol yeah well if you're using figure 8, I have no idea. Never managed to either make it work or see the point of using a sling long enough to make it the only viable method lol It just looks so cumbersome in the videos :-)
But if it works for, you go for it :-)

But with other methods it's usuallly the shoulder that gives problems - I find. the arm is invariably straight so little stress is put on any other joint (maybed fingers lol)

I wanted to write more about anticipated adventages and disadventages of the sling with sliding booster mass. But some of you already have written about most of them. So not much to add here.

Dale,


Quote:

This whole idea reminds me of a roller-skating maneuver called the "slingshot"...

You are right. A similar (the same?) effect is used to accelerate interplanetary spacecrafts. The BIG mass of the planet attracts the spacecraft and curves its trajectory. As a result, the spacecraft is speeded up. The additional energy is delivered by the gravity field of the planet. In case of the metnioned sling, there is a very similar situation. The main difference is that the projectile is attracted to the booster mass due to its knetic energy (its sliding on the cord). This is a one of ways of transfering the energy. The second one, desribed by Matthias, is "qausi-double-pendulum effect", which seems to be only way of transfering whole the energy in his design.

[quote]...Would the moving booster mass, slow down the swing and assist the momentum transfer?[quote]

I think you mentioned just the third way :) Damn it, all it becomes too complicated to me  ::)

The main enemy in this design seems to be the friction between the cord and the booster mass. It should be reduced to the minimum.


Jurek

Quote:

...At first glance, I don't think that it will give you enough time for the pouch to come around. It might also be pretty hard on your hand if it slid any distance (no pinky loops, remember) The _good_ news is that it might just put the booster out of danger range, allowing you to ground out a failed throw!...

Matthias,

All it you mentioned above depends on how the sling would be adjusted (lenghts, distances, masses etc.), and as result how much the energy of the booster would be consumed by the projectile. At my guess, there is a bigger chance for the pouch to come around just due to the permanent tension and the shorter and shorter cord.

Jurek

FunSlinger wrote on Mar 27^th, 2007 at 12:49am:

I don't quite understand the desired goal. It seems like the gadgetry being described will add an element of chaos into the equation and could potentially make it harder to be consistent, accurate, or even safe when slinging. But I'm not a mechanical engineer and admittedly don't quite follow the mechanics being described and the diagrams.  :-/

FunSlinger,

The same is when people make elaborate braided, waved or knit slings. Not always they are utilitarian, though. Designing and making them is just a fun :) Believe me, If ever have a chanse to make an effective compound sling, a simple classic sling will stay my favourite "evryday" one though.

Jurek

Dale,


Quote:

...Of course, I will have to get my rig working before Jurek gets his working, or I've got NO chance of making the record book. ;)

If I ever try to do that, I'll use an usual simple sling which will cost no more than 1$, so no rush ;)

Pancaker,


Quote:

I haven't done the math, but it seems to me like the timing of the two releases would depend not just on sling lengths, but also on the ratio of the booster mass to the pouch+glande mass. It would be great if, for a known booster mass, the sling would have a series of markings such that for any given glande mass you could use a marking to compensate for the mass effects.

If you could do some math, I would love to see results. Great idea with the marks!

Quote:

It's easy to confuse angular velocity with speed...

I'm pretty sure it doesn't happen to you, Matthias.



Quote:

...Shortening the radius of a spinning sling does speed up the rotation, but the projectile is still moving the same speed...

It's easy to forget that the above is true, only when no energy is provided to that system. Conservation of energy and all.



Quote:

...all you've done is made it harder to judge the moment of release

It sounds like you really know what you say.

Jurek - I wasn't at all suggesting that you had made any unfounded claims, but it is something to watch out for, and that tends to come up every now and then when talking about  more complicated slings. As I'm interpreting your design, the genius in the sliding weight setup isn't so much that the sliding itself speeds up the sling but that it maintains tension on the secondary cords in the critical initial phase.

All I was trying to say is that reducing the radius of rotation doesn't speed up an object by itself. Thinking only about a conventional sling, suddenly shortening the cords would seem to make it much more difficult to throw.

I'm not sure that a gravitational slingshot works similar to either of the cases here. There are all sorts of complications with frame of references and varying forces... Once we figure out how to sling rocks faster than normal we can move on to sattelites and planets ;)

Matthias

Beautiful results!

This is a first pass simulation using the sliding booster. I kept the same ratios as what I've been using for the masses (6:1), and Jurek's 1:1:2 for the locations of the booster, stop and pouch. The first picture is constant energy - I brought the system up to speed and then let it "coast" through the release. There is an almost total transfer of KE with this setup. Constant torque gives similar results. If you can manage constant speed (in practice you'd need a heavy staff-sling type setup) you really spike the power to the glans, picking up an extra 75% or so, but of course the torque input requirement is extreme to match.

http://img.photobucket.com/albums/v349/mhborstad/JurekKE.jpg

http://img.photobucket.com/albums/v349/mhborstad/JurekT.jpg

A closeup of the model and release mechanism. The cam-slider is acutated by a constant-speed "cylinder" that pushes the release knot up over the lip at the appropriate time.

http://img.photobucket.com/albums/v349/mhborstad/JurekMech.jpg

Pretty cool... Even without using the booster to trigger the release the sliding mass certainly looks like a great solution toward keeping the cords tensioned. Who know how it might work in real life - only one way to find out... If we could double speeds as easily as you can in simulation ::) we'd all have to find bigger places to sling!

Matthias

Uh-oh... I just noticed that the booster didn't make it all the way to the stop before running out of steam. I guess this is great from an energy standpoint, but it makes it tricky to use it as a trigger. Some fine tuning required! I'll try lengths first, then fiddle with the masses...

Matthias,

For the sliding booster mass, I agree that the changing of the radius does not change its linear speed. No gain there. However, as it slides down the cord, it acts like a pulley with a 2:1 mechanical advantage. Its effect on the pouch is not only to change its turning radius, but also shift its center of rotation. If the decreasing booster-to-pouch radius does not contribute to the linear velocity of the pouch, would the shifting center at least do something to help?

Someone mentioned the shock that a slinger would receive from the sliding booster weight sliding away and suddenly stopping.
Someone also mentioned high friction wear on the cord under the booster weight.
I think neither of those problems should be too bad. Unless the booster weight is enormous compared to the glande+pouch, it imagine it should slide slowly (relatively speaking) precisely due to the high friction of a bent rope and the energy being transferred to the pouch.

Jurek, although I'm no physics major, I will try to work out some calculations for more than just hand-waving arguments. But with Matthias' excellent knowledge, and his simulations, that might end up irrelevant.

Also, props to Shabundi for your very intelligent questions and contributions.
Great work everybody! To me, this is by far the most exciting thread in a while.

Matthias, your piston&cam mechanism releases the primary release cord when the main sling arm reaches a constant angular velocity, right?

Maybe a spring to control it's 'sliding'?

pancaker wrote on Mar 27^th, 2007 at 10:36pm:

Matthias, your piston&cam mechanism releases the primary release cord when the main sling arm reaches a constant angular velocity, right?

For this simulation I start the thing running with a constant angular velocity and then just let it run. The release ends up just being timed. Seems to work ok, and the constant KE case seems the easiest to work with for now. What happens during the "snap" is going to be another problem.

Both your and Jurek's explanation of the acceleration due to the booster seem on. It's hard to tell what exactly is going on - even with the sumulation all instrumented up. What proportion is due to the outward shifting center and what is due to the tangentially shifting center? What does seem clear from the sim is that the sliding weight seems to "self-tune", which might be the magic trick that makes this whole thing work:

For a given weight and length ratio, the secondary release arc is pretty much constant, regardless of speed. The way the sim posted above was configured, you hit max V about 90 degrees after releasing the secondary. You can adjust the arc with either length or weight. How far out the cord the booster runs is also a mass problem - angular speed doesn't look to play. So there are three tools that each tune the three most important aspects of the throw mostly independently, and it just might be possible that one tuning could work through a range of slinging speeds.

The tension and handshock issues are a bit funny. The second you drop the pouch, your perceived tension drops way down, before smoothly increasing again up to a maximum when the secondary hits apogee. With a "hard" trigger in place, it looks like a pretty solid tug. The timing gets tricky too.

Basically the booster slides out until it has dumped all of its energy. If we're going to use it to trigger a release mechanism, it still needs to be sliding when it hits, so we have an inefficiency as well as the hand shock issue. It's not moving outward too quickly at the end of it's short little run.

I think the friction should be manageable as well - except for maybe the first instant, when the sling is folder 180 and sliding quickly. The booster might need some care. Wear isn't likely to be too bad.

Maybe Dravonk's release combined with an unrestrained slider would work? Then you'd have a simplish sliding booster and a relatively reliable release... Getting a bit complicated, but I still think there is great potential. Looking at the tensions and timings, I'm still not "quite" convinced that this isn't doable with a manual release. Jurek's sliding weight seems to smooth things out a little, but tragectory control is still going to be tricky.

Thanks everyone for playing along!  :) Just in time for spring.

Matthias

Just to be clear! The pistom-cam-thingamabob is just so that I can get the thing working within the constraints of the software. Not suggesting anything like that in real life ;D. I thought that if anyone wanted to play around with the demo I'd include enough info to reproduce my work.

I didn't post the one with the working pouch or contact-release trigger ::) there's a Rube-Goldberg sling if you ever saw one!

Wild idea, this compound sling!  I love original idieas, unlike a lot of other people, apparently! ;D

I love playing with ideas and also love slings so this one has huge play potential, thanks.  I have an idea about it which I am unlikely to be able to try out soon.  It is a little less sling like but could, if it works, solve the releace problem.  What if the final two stages after the weight were disposed of and replaced by a tube, attached to the weight by a hinge and closed at the same end.  One would sling as normal with the weight taking the place of the pocket and on releace the tube would unhinge, the projectile ( a sphere would be a good choice, which had been adjecent to the weight during the cast would roll down the tube and fly out the end.   I think that much of the energy of the weight would be trancefered to the projectile, if ever you've used a tube to flick marbles or ball bearings you'll know the principle.  The only problem with this that my mental simulations come up with is that one would be slinging backwards.

Better idea.  Simply weight the end of the tube at the closed end.  O = open tube, c = cords attached here, w = closed and weighted tube, p = projectile start point.

  OOOOOOOOOOOOPWC

This would just replace the pocket and release cord on a standard sling.  I've played with a similar idea, minus weight and with less tube and more cord ( Just a pipe pouch really )  with a view to keeping multiple shots tight.   It worked in one plane, one gets an arc of shot.   So one can certainly cast from a tube.

Or for a double whammy, extend the entire thing, add a cord to the open end of the tube, and a second weight on the retention adjecent to the open end ( sling folded ) with another cord extention from the second weight to the hand.

 CCCCCCCCCCCCC.OOOOOOOOOPW.CCCCCCCCCCW.CCCCCCCCC

I suppose one could keep adding extensions indefinatly ending up with the deadliest grain of sand ever.  Maybe that part is over the top.

The tube idea may be easier to test if one made it one tube within another, as one could fiddle with length.

HELP!!! My primitive incendiary-oriented mind cannot handle this massive overload!!!!!!

Quote:

I'm not sure that a gravitational slingshot works similar to either of the cases here. There are all sorts of complications with frame of references and varying forces... Once we figure out how to sling rocks faster than normal we can move on to sattelites and planets

Matthias,

I still see that analogy, not so I'm as obtinate as a mule, I just see it in that way. Of course, thre are some differences and complications, but the principle in both the cases is the same for me. And I think that sometimes it is good to reach stars and planet first. Maybe someday we will reach them with a super-hiper compound sling ;)

Jurek

Matthias,

Really good news! It sounds very promisingly. I have downloaded the simulator to play with it, but it don't want to start on my computer at all. I will be trying to make it work. Anyway, looks like cosmic forces of Mother Nature further us and there are just a few small technical details to solve. However, the devil is in the details.

Jurek

Pancaker,

The pulley example is a very good one. I was thinking of useing a sort of pulley, but it would create problems with the sling orientation during wind-ups. It would be the best solution to reducing the friction on the cord. I don't fear it could be a reason of wear and tear of the cord. A much worse thing is waste of the kinetic energy of the booster mass. As I said before I'm pretty sure the friction is the biggest enemy of efficiency of the sling. The less friction, the better energy transfer.

Since Matthias is able to do such excelent simulations, it would be waste of time to do "hand-made" calculations indeed.

I love simulators and math results either, but they would be useless without human-brain-intuition simulators, isn't it.

Jurek

Quote:

...Jurek's sliding weight seems to smooth things out a little, but tragectory control is still going to be tricky.

Matthias,

Im affraid it is a price we would pay in different ways in every design. For example, in that one with the fixed mass, it would be necessary to control either the double release (I can't imagine to do it manually) or whole that sensitive for timing "double-pendulum-like dynamics". Not saing about a special slinging technique, and the loosening cords.

On our desire, a whip like a sling (or a sling like a whip), only the small piece of the tip could do the good work. How would it be controlled? I have completely no idea.

I have realized that the sling with the slide mass works in a very simillar way to a whip when it is cracking. The end of the whip goes through an invisible pulley, which becomes smaller and smaller,  due to the narrow shape of the whip and its changing rigidity. It gives a material for thinking, isn't it ?


Wow, the topic is really exciting.

Jurek

Yurek wrote on Mar 28^th, 2007 at 4:47pm:

I love simulators and math results either, but they would be useless without human-brain-intuition simulators, isn't it.

Indeed. Too bad it won't run on your machine Jurek - it's a fun little program, and not too hard to get a handle on. Not to say that actually coming up with virtual mechanical devices that actually DO what you want doesn't require a whole heaping pile of human-brain-intuition! But that part is fun too... :)

Looking at the sliding weight simulation some more, I'm not entirely convinced that friction losses amount to anything. Even if the weight is fixed, as in my original drawing, the energy transfer seems to happen the same, but without the auto-tune benefit. So long as the weight moves smoothly, without jerking it might just work.

I've built a prototype... Tennis balls. Included-angle release hook. Sliding booster (possibly highish friction). Maybe if the park is empty this afternoon... I did a low speed "test" in the backyard spinning slowly in a plane around my body and it seems to work perfectly ::). Small yard... bad idea.

I might even go so far as to say that I'm optimistic! My release hook needs beefing up though - I'm not sure if it will handle even the tennis balls with a real throw behind it. I'll start slowly, and see if I can't shoot some video.

Matthias

Yurek wrote on Mar 28^th, 2007 at 5:38pm:

[quote]Im affraid it is a price we would pay in different ways in every design. For example, in that one with the fixed mass, it would be necessary to control either the double release (I can't imagine to do it manually) or whole that sensitive for timing "double-pendulum-like dynamics". Not saing about a special slinging technique, and the loosening cords.

If everything works the way it is sort of looking that it might... A sling that fires at the same arc point every time combined with a release that fires at the same extension angle every time. You just might be able to aim the thing almost every time (tangling is as ever an issue).

Whips, slings, planets... Enough to make your brain hurt ;D If we can get this simple "two-part" whip/sling/thing going we'll have to figure out a distributed mass version! While we're at it we still need to find a way to make louder whip-slings (a completly different problem ;))

Quote:

Looking at the sliding weight simulation some more, I'm not entirely convinced that friction losses amount to anything. Even if the weight is fixed, as in my original drawing, the energy transfer seems to happen the same, but without the auto-tune benefit. So long as the weight moves smoothly, without jerking it might just work

You most probably are right, in a case of a bigger friction, the way of transfer the energy would be changing. But friction isn't prnament on the whole way of the booster, it might make additional problems with timing.

I'm happy to hear about the postive results of your test. I will think about doing the same. But now there is the time for me to land from the space just to the bed :)

OK... it works. It seems reliable. It seems like aiming (downrange at least) won't be a problem. It needs a few kinks worked out. It's very scary.

Even with tennis balls, I didn't have enough room (and too much common sense) to try anything but a relatively gentle throw. I only got a dozen or so in, but it's a start. Ranges were around 75m shooting flat. Nothing special, but also nothing like the effort I was putting in. A higher arc, rock and some oomph should be a different matter.

The sling is ~1m, with a 1lb (450g) lead ball acting as a sliding booster (too heavy!). Hook shaped auto release triggered when the secondary opens almost to it fullest extent. The release is at 50% of the retention cord, and there is a standard split pouch on the end.

http://img.photobucket.com/albums/v349/mhborstad/CompoundTest1.jpg

http://img.photobucket.com/albums/v349/mhborstad/CompoundTest2.jpg

http://img.photobucket.com/albums/v349/mhborstad/CompoundTest3.jpg

The mechanics are easy, wind up like usual, release the pouch a bit early, watch the rest unfold on autopilot... Releasing early is counterintuitive - you can see that my shot goes left of where I'm looking - but that's just practice. You need to watch out for tangles, but other than that it takes care of itself. The booster wasn't at all a problem after firing - well behaved. If the secondary fails though it is a little hairy - that energy has to go somewhere. Putting it into the ground was no trouble, but something to watch out for. Once we graduate to overhead throws it might bear some more thought.

http://img.photobucket.com/albums/v349/mhborstad/CompoundTest.jpg

To do:

• Streamline the sling. No tag ends, nothing to tangle.
  
• Anti-twist cords. Although thin cords are good, cords that twist don't help here.
  
• Better release hook. Shaped from a piece of plate would be nicest. This one worked ok, but I'd like something tidier and more stable.
  
• Weight ratios
  

A first step anyways! I'm pleased 8-) I'd post the video but at 30fps the entire interesting part falls between frames, even with this lob...

Matthias

It's really great to see new, original ideas, and out-of-the-box brainstorming comments being welcomed on the forum once again, rather than merely being ridiculed, and put down with a dismissive, oh-so-venomous tongue-in-cheek comment!      :-X

This one is a real winner, whether or not it turns out to be workable.  I, as the resident champion of the unconventional,  hope that it flies farther, faster, and more accurately than any sling in history ever has!  But then, again what do I know?  I still think that the Assyrian soup spoons were really just long-tailed toli sticks!  8-)  They were there to protect the Assyrians from ancient long bows because they were unable to defend themselves with their "inferior" Asiatic composite bows, which although lighter, shorter and easier to carry and shoot further accurately, especially when fired from horseback, than the long bow, were still inferior somehow, and were just invented due to the lack of decent bow-making materials on the steppe (yeah, and General Lee mistook shabbily-dressed Ulysses S.Grant for a blacksmith, and handed him his sword a Appomatix court house for Grant to polish!. ::)  The solution?  Use the long-tailed soup spoon toli sticks to shoot white-hot, wind-heated charcoal-coated glans and set their bows on fire! YEEEEAH!  ;D

Hey, how about this one...a compound toli stick for hundred-yard field goals every time! :o

But seriously...(which I seldom bother to be (serious, that is!) anymore, but here goes...) I believe that creative, and visionary thinking such as this idea, and others like it on slinging.org may result in a LARGE vartiety of new and unique tools, weapons and other useful inventions which may someday be remembered in history as having inspired many new and life-changing technologies, as well as an environment of intellectual freedom and mutual inspiration for those of us who occasionally find too much time on our hands.

Quote:

remembered in history as having inspired many new and life-changing technologies

That's a tall order for such a simple tool.....you really think the lowly sling might someday be taken to such a grandiose height as this?


TS

lmao - good to see you back ts.

No idea what soup spoons have to do with this topic - assyrian or otherwise - but excess enthusiasm is probably better than none at all, and hey you never know. The bloke who invented cats eyes just wanted a way to get back from the pub while tanked up on misty nights - he changed the world for the better. Big ideas can have humble beginnings  :-)

And Matthias - wow - you made one and it worked, now I definitely want one :-)
75 metres with a tennis ball is pretty good they don't fly particularly far in general.

Yesterday I played a bit with connected pendulums. I fixed a ring with four keys in the middle and a single key at the end. It was quite impressive to see the energy of the key ring going to the single key completely. It just looked a bit too slow to happen during a wind-up. Matthias, did the booster weight slow down almost completely in your tests?

After my pendulum test I felt the temptation rising to build a real sling like that...

Dear Techstuf,

If it ever does take off to such grandiose heights, it will be thanks to members like you, Matthias, Tint, Aard, Lobohhunter and perhaps even little old me (part optimist, part curmudgeon), ....Underdog!   :-?  ...among several others.  It never hurts to encourage our people with some shameless, "magnumslinger-esque" cheerleading, however!  I really think that there are many here who could make it happen, intentionally, or otherwise.  Yeah, some significant inventions will probably someday be traced back to this forum, eventually!

Aardvaark!  How's it going?  I was refering to several posts where I tried to get/continue or stimulate discussion here by reeling off wild ideas, etc.  (It usually worked, thanks to you, and others who were kind enough, and/or at least interested enough to comment on them!  :P )  The "soup spoon"part  was a reference to the old pictures where it looked like the ancient Assyrian slingers were throwing stones from soup spoons, which I mused were more likely to turn out to be toli sticks, or Philippine bamboo stone throwers!  I left out that Irish-American wild Astrology-history-Egyptian-Biblical site you got such a kick out of!  By the way, here's a couple of sections from another interesting one with some similar references, but one that I enjoyed even more:  

http://www.theosophical.ca/Book12A%20-AncientEgypt.htm

http://www.theosophical.ca/Book4AncientEgypt.htm

There were no cool "ancient-solar-heroes-slinging-from-horseback-at-evil-giant" cartoon pictures, or even any fun "Prehistoric Irish mutant ninja druid-kings-as-unjustly-dethroned-masters-of-the-ancient-world" conspiraciy theories on this one, though!  :-/

Feel free to either tear it apart, comment unenthusiastically, or praise it, as you see fit!  Either way, I think you'll have some good insights to offer, as usual! ;)

Matthias-

How are you holding onto the projectile when you swung your prototype?  Did you have any problems with dropping the ball before/during release?

(I'm tempted to build my own version of this.)

Could the booster weight be more oval shaped or otherwise elongated in shape with the cord attaching on each end of it? I'd think it would be less likely to tangle that way.
 
    What about just drilling a hole lengthwise through a lead weight and using a piece of heavy guage wire bent into an eyelet at each end? Of course, this would prevent a series of weights for different weghted glans.

Matthias,

In your design, does the booster weight actually slide along the cord?  If so, what stops it?  Seems like it would tend to tear the cord at the release gadget.

Quote:

75 metres with a tennis ball is pretty good they don't fly particularly far in general.

It's about as far as I can throw one comfortably with a standard sling. The motion feels funny - as the ball *shouldn't* go as far as it does...


Quote:

Matthias, did the booster weight slow down almost completely in your tests?

Pretty much - my masses weren't balanced, which I think allowed the booster to hit the release hook, stopping the outward motion and allowing it to retain more energy than it otherwise might. The speed was definitely cut to around 1/3 or less of the pre-release speed though. If the secondary doesn't fire for some reason the difference becomes very apparent. The sliding mass should basically adjust itself for maximum energy transfer: in a properly working compound, prematurely stopping the weight (not enough sliding room allowed) and releasing the secondary early (not enough time/arc allowed for the transfer) will be the main factors. You are always going to lose a little from the release point, unless someone comes up with an instant release that works at exactly 180 degrees. My sling is supposed to dump somewhere between 160-170, which is adjustable by the length of the trigger cord. Making the booster lighter relative to the thrown mass shortens the amount of sliding required.


Quote:

...FunSlinger rasises a bunch of good points...

Normally, I'd splice all the connections in a sling like this for smooth transitions, but whipping would work perfectly as well. The reason I left knots with long tails was that I wasn't certain that I wouldn't have to adjust everything.

I think possibly a more streamlined, organised booster FunSlinger describes might help with a fixed-position design. The booster I was using slides, which seems to be a big help, though with this trigger the fixed one might be manageable as well. Apart from the seeming automatic tuning benefit, the huge advantage is that it puts tension on the cords through the first moment of release, which makes the whole thing much more predictable.  I think that you could actually get away with a small pulley and snap-hook masses clipped on without worrying too much about tangling. The booster stays nicely out of the way of the whole process because it is being held outward by the slinging forces.

A plate/jigsaw-blade hook seems like a good idea (waterjet cut would be really nice - anyone have one in the garage?) One of the problems with the geometry I used is that the secondary retension cord interferes a bit with the hook - and the wire loops make it worse. Rather than using a single piece retension cord as shown, I suggest that a better design would use three holes in the hook, and break the cord at that point. This should help with the tangling a bit by keeping the hook straight and the troublesome crossing will be eliminated.


Quote:

...Funslinger talks about compound-whip-slings...

I have absolutely no idea. That could go in the simulator pretty easily though.  ...Thinking... hmm, I think I could see it working pretty well. Aiming would either be easy or really really hard. Who's going to build one for a real world test? I won't be back at the simulator until mid next week.


Quote:

How are you holding onto the projectile when you swung your prototype?  Did you have any problems with dropping the ball before/during release?

I just hold the pouch. No trouble at all with dropping, but I never drop anything with a normal sling either. The test sling uses a woven split pouch that I had left over from the tutorial I wrote a while back. It holds the tennis ball pretty securely. The trick with pouches is that you really want to hold the projectile with the outside edges if at all possible. Support it from the middle and it's apt to roll around.

Jurek's sliding booster fixes the release mechanics perfectly. What would otherwise be a pretty complicated manoever with potentially slack cords and unreliable timing becomes as easy as a standard release!


Quote:

Could the booster weight be more oval shaped or otherwise elongated in shape with the cord attaching on each end of it? I'd think it would be less likely to tangle that way.

It could (see FunSlinger reply). I'm thinking of going the opposite direction though, and using a pulley and maybe even a short length of cord to get it away from the sling (remember that the sling is folded through the working phase).  As complicated as the design looks, it is really easy to load and seems pretty tangle free. My main problems were cord twisting and tangling at the retension hook.


Quote:

In your design, does the booster weight actually slide along the cord?  If so, what stops it?  Seems like it would tend to tear the cord at the release gadget.

It does slide - you can see clear evidence of this in the photo if you squint. The sliding is what makes dropping the pouch work as well as it does, regardless of the contribution to energy transfer. As for stopping the sliding - It stops itself. Amazing but true! So long as it isn't so heavy that it can make it out to the hook before dumping the remaining energy, it stops sliding as the secondary reaches max extension. If you look closely at the second simulation I posted you can see the path taken by the mass, including the point where it has stopped moving (both outward and tangentially). In that sim, the secondary doesn't dump, so as it comes around past 180 degrees, it reaccelerates the booster and starts sliding it inwards at the same time...

The sling should be tuned so that the mass doesn't make it to the hook. In the test rig, I "think" I'm hitting, but can't tell with the speed everything unfolds at. Lowering the ratio of booster to thrown mass or moving the retention hook outward a bit more would both work. I don't think the second is necessarily a good idea though, as the shorter secondary would put bigger demands on the system.

Once the secondary fires, there is nothing to prevent the booster from sliding out to the end. A stop before the hook is a good idea to prevent trouble with this critical part. The further extension of the primary length after release is helpful though, as it slows what's left of the rotation down even more.

******

I look forward to seeing some Mark II compounds posted. Weekend's coming up!

Matthias

I do not think mine qualifies as a "Mark II", but I am working on one.  I am duplicating your design, Matthias, but using Prusik knots everywhere so I can tune it easier, and the booster mass is an 8-ounce (227g) sinker (since you said 16 ounces was too much).  Your experience has convinced me that sliding booster and automatic release are the way to go.  The sliding booster automatically puts tension on the release cord and keeps you from fouling the sling or dropping the ammo.  The automatic release means there is one less thing to keep track of in my hand, and I have enough trouble walking and chewing gum at the same time.  I'll let you know how it works.

By the way, how did you do that multiple-exposure photo?  A series of shots, merged in Photoshop?  How'd you get your camera to snap photos that rapidly?  That has to be faster than 30 frames/second...

My impression with Matthias' first scheme with non-sliding booster weight is that this booster weight is not for boosting but for making the first string controllable independent of the second string. What would be interesting is a variant of a staff sling. Take e.g. a 70cm carbon fiber stick and attach a sling to that. The release could be some kind of remote compound bow release. The stick would be controllable thereby allowing a lot of different motions. Or it can just lengthen the arm. So that would be some merger of sling and staff sling.

But first I have to get my normal slinging working. (Btw. there is no flash plugin for Linux x86_64. So I can't look at the new member map.)

Zwiebeltuete

I tend to agree with Zwiebeltuete.

I think it might be seen as carrying the 'effective' hand of the thrower to the middle weight, so just scaling up the size of the slinger. In that case I would expect for a good match the outer 'sling' to be exceptionally long. I'm not sure what sizes are practically being considered here.

A great thread. And Yurek's sliding weight concept looks truly amazing. One has to wonder why the ancients didn't figure this out, particularly since it has such a well defined starting configuration etc.

wanderer wrote on Mar 30^th, 2007 at 9:16pm:

One has to wonder why the ancients didn't figure this out, particularly since it has such a well defined starting configuration etc.

Once they figure out how to make crossbows, the popularity of the sling diminishes fast.  

I think a crossbows are simpler than what we are trying to make on this thread.

Tint wrote on Mar 31^st, 2007 at 6:31am:

I think a crossbows are simpler than what we are trying to make on this thread.

I thought I heard that crossbows were more expensive than bows but just became widespread because they were easier to use than a bow, or did I get it wrong? I'd guess the sling just disapeared from wars because of the staff slings and the first guns.

Quote:

(waterjet cut would be really nice - anyone have one in the garage?)

If I knew what it was I could probably acquire one :-)

okay slings fell out of use in battle for several reasons. 1) you can't aim a sling.
Even a complete idiot can sight down a crossbow.
2) you can teach someone to hit a barn door at 50 yards with a crossbow in about 5 mins (assuming you throw in a bit of safety about not putting your finger in the way of either the winding gears or the cord once you pull the trigger)
It takes several days to get someone even halfway competent enough to hit a barn at fifty yards with a sling - and there's no guarentee it'll go through the door at that.

It's as simple as that. crossbows are pretty much skill free for basic use.
Even bows require technique and training.
If you invest that training then a bowman will outshoot a crossbow.
But both can be aimed and are more effective for battle than a sling, given how many trained crossbowmen or bowmen you can get in the same time you can turn out trained slingers.  

For practical purposes there's just no comparison I'm afraid.

correlating a couple of threads.
So could a smallish compound sling be used to sling paintballs or other low density ammo ?
In which case I definitely want one as I've got 2000 bloody paintballs sitting around waiting for some way to hurl them at trees :-)

i've got it! i didn't really read this topic before, and now that i skimmed over it's 6 pages it took me half an hour, because i didn't percieve funslingers diagram. the release mechanism was a mistery to me, but now i've got it.

damn it. i won't be at peace untill i've tried this one  >:(

Well, I got my replica of Matthias's compound sling built, and tested it. About a dozen throws, of which two were decent (except that they took off 90 degrees to the left of where I intended).  The other throws were complete flops.  I believe that my automatic release was too eager.  Several times it released as I held the sling before even starting a windup.

When it did work, releasing the pouch from my hand was no problem at all.  The sliding booster mass (an 8-ounce fishing sinker) kept the cords tight.  The booster slid all the way down to a stopper knot, and did not stop of itself like Matthias described.

Tuning the rig (getting all the cord lengths just right) is going to take a while...

Curious Aardvark wrote on Mar 31^st, 2007 at 12:51pm:

okay slings fell out of use in battle for several reasons. 1) you can't aim a sling. Even a complete idiot can sight down a crossbow. 2) you can teach someone to hit a barn door at 50 yards with a crossbow in about 5 mins (assuming you throw in a bit of safety about not putting your finger in the way of either the winding gears or the cord once you pull the trigger) It takes several days to get someone even halfway competent enough to hit a barn at fifty yards with a sling - and there's no guarentee it'll go through the door at that. It's as simple as that. crossbows are pretty much skill free for basic use. Even bows require technique and training. If you invest that training then a bowman will outshoot a crossbow. But both can be aimed and are more effective for battle than a sling, given how many trained crossbowmen or bowmen you can get in the same time you can turn out trained slingers.   For practical purposes there's just no comparison I'm afraid.

I'd say improved logistics killed the sling. Battles are won by superior weapons, wars are won by superior logistics. The sling is an extremely simple weapon. It only requires materials that are easily available everywhere (cord, cloth or leather), while powerful bows require special forms of wood. Composite bows are even more difficult to make. Crossbows are medieval high-tech, no less.

Slings can shoot stones or metal bullets, both of which are easy to obtain. Arrows and crossbow bolts require serious technology and skilled craftsmen (this is where all the people called "fletcher" or "arrowsmith" come from).

Of course, one can make bows and arrows in far simpler ways, but these hardly beat a sling.

So, when you have a supply system that transports bows and arrows to the front, the bow rules. If not, the archers can only run while the slinger keep shooting.

I agree....and would go so far as to suggest that we all want to see some success stories even more!


TS

To be honest, now that I know it CAN work, I have put it aside because it will take more time than I have right now to make it work RIGHT.

I'll get back to it one of these days ...

No slinging, compound or otherwise, for me in the forseeable future... Summer's coming though, so I have high hopes.

I've seen enough to have satisfied myself that the idea can/will be made to work. I'll even go so far as to say that it should be easily controlable and "relatively" safe. A better automatic release mechanism and some refinement should be enough... Further down the road there is lots of room for play.

Matthias

What could possibly keep you from this singularly intriguing pursuit throughout the spring?


TS

Bivalves

Touche'.....that does sound doubly intriguing!


:o


TS

So, this member of the Flower Generation might get away with saying that you dig clams?

Ba dum bum!  (to quote TS)

Everybody.......


(insert collective painful moan here)


That wasn't just unfunny.  It was somehow...diametrically opposed to funny. Peculiar, really.  You seem to be employing some innovative sort of active humor cancellation.  What is the source of your technology?


LOL


TS

Aww, come on, it wasn't THAT bad ... was it?  :-/

Ok, I read ya.  ;)  (it's proprietary tech)


Yes Dale, it was pretty pungent.  


Bada Bing!


Get it?  Pungent!


Just keepin it real. You old rainbow warrior you....


TS

Ouch!

Hey!  I think I just found where Matthias got the idea for this compound sling!  It is in a post from a member by name of Me, almost two years ago, in this post. Matthias's response, in the next post following, shows that the Idea had been planted!

Where is ME these days....he was a font of ideas, that one!


:)



TS

i need to get on more. anyway, i didnt have time to read the whole seven pages but do you think it could be adapted to shoot two bullets on one sling? maybe a high lopb then a straight shot?

it would be heck to aim though.

just thought I'd bring this one back for the slew of new members we've had recently :-)

The future of slings ? or just another way to dislocate your shoulder ?
You decide :-)

I’ve been pondering this “compound sling” idea and I wonder if this would work:

Let the lower (closest to the slinger) sling pocket have the heavier weight sewn in and the top pocket or pouch free to launch the bullet.  This may have been mentioned in one of the posts, but I got so confused reading them that I don’t remember.

If you do this, you must do a “recovery” so that the heavier weight doesn’t break you or someone near you.  But if you can do a basic “wind up and wind down” with a standard sling, I don’t think this would be a problem.

Now: everybody tell me what I’m missing.

Trebuchet
8-)

you're not missing anything that's essentially the idea.
And dale - the initial principle was mine, sorry :-)

It's based on the fact that you can exert more of your muscle power on a slow throw with a heavy missile than you can with a fast throw with a light missile.
So the object is to take the energy put into the heavy weight at a relatively slow velocity and transfer it to a much higher velocity with a much lighter missile.

Curious Aardvark wrote on Oct 5^th, 2007 at 12:13pm:

you're not missing anything that's essentially the idea. And dale - the initial principle was mine, sorry :-) It's based on the fact that you can exert more of your muscle power on a slow throw with a heavy missile than you can with a fast throw with a light missile. So the object is to take the energy put into the heavy weight at a relatively slow velocity and transfer it to a much higher velocity with a much lighter missile.

Whoever originated the principle - my recollection is that the truly original feature of this thread was Yurek's sliding mass.  

wanderer wrote on Oct 5^th, 2007 at 2:57pm:

Curious Aardvark wrote on Oct 5th, 2007 at 12:13pm: you're not missing anything that's essentially the idea. And dale - the initial principle was mine, sorry :-) It's based on the fact that you can exert more of your muscle power on a slow throw with a heavy missile than you can with a fast throw with a light missile. So the object is to take the energy put into the heavy weight at a relatively slow velocity and transfer it to a much higher velocity with a much lighter missile. Whoever originated the principle - my recollection is that the truly original feature of this thread was Yurek's sliding mass.

Folks, if we keep this up we're going to "high tech" ourselves back into the stone age.   ;D

Trebuchet

Well the whole thing started 'cos I wanted some way of imparting more velocity to paintballs or other missiles too light to throw easily.



Quote:

my recollection is that the truly original feature of this thread was Yurek's sliding mass.

Umm, the whole compound sling concept is pretty unique :-)

Curious Aardvark wrote on Oct 29^th, 2007 at 10:30am:

Well the whole thing started 'cos I wanted some way of imparting more velocity to paintballs or other missiles too light to throw easily. Quote: my recollection is that the truly original feature of this thread was Yurek's sliding mass.   Umm, the whole compound sling concept is pretty unique :-)

Well - I stand by my statement :D.

First off, my limited understanding of the concept of a Compound bow, is that it makes it more powerful, but most importantly more accurate.  Standard Bows are limited to the size of their user, so you are limited by your height to the power you will get out of a standard bow.  They can tell the height of people on the Marie Rose by the bows on it.  The point being you can hold and aim a compound for a lot longer than a standard.

What if you used something like a skipping rope, (modern boxing ones can be weighted), or tubes with ball bearings to replace the stings.  Giving you a sling that is weighted aroung the pouch.  Would this not unable you to spin it faster, and give it more energy on release?

Excellent idea. I do not quite understand the physics behind it but I do know how much that would hurt if you got hit from one of those babys. I wonder if you could go through a person with the right projectile.

minotaur a weighted pouch would enable you to sling light objects - but is a different concept entirely from the compound sling.

the basic idea is that you can safely put a lot more effort into a slow but powerful throw with a heavy weight than you can with a light weight. the compound sling takes the energy imparted to the heavy object and transfers it to a much lighter projectile that can then be thrown with a much higher velocity than would otherwise be possible.

I blame paintballs - as it's why I came up with the idea in the first place.
it took everyone else to work out how to do it :-)

So how come we haven't seen a paintball-compound yet hmm? I think it could work quite well, and it should certainly be safer than messing with the full sized variety! One of Hondero's ball-in-a-cup releases would be perfect no?

Matthias wrote on Nov 14^th, 2007 at 2:54pm:

So how come we haven't seen a paintball-compound yet hmm? I think it could work quite well, and it should certainly be safer than messing with the full sized variety! One of Hondero's ball-in-a-cup releases would be perfect no?

Interesting thread, I have to read it in depth. I cannot avoid the idea of a hammer thrower spinning himself with his seven Kg. weight and shooting his compound sling that propel a 30 gr.  glans to a mile of distance  :D.

Now you've got it ! that's exactly the idea :-)

Well matthias - I can't figure out how you make it work and you never sent us one for slingfest.

But the tube sling thing that loki's made ought to work for paintballs.

Here's an old thread that I thought I'd bring to the top for the benefit of some of the newer people.  I found it a while back, and I've been tinkering with the concept.  I think I might have it figured out too... we'll see.  I'll get some pictures up when I get some ;)

ooh - now that would be cool. I still have 1000 paintballs :-)
Dale and matthias reckon they got one working - but never took any pics :-(

Here's a quick rough scetch done in MS Paint to demonstrate what I'm thinking about doing.  The hook displayed on the full sling is not to scale with the rest of it in case you were wondering.  The handle section has the cord passing through it, and the excess cord wraps around the handle.  This allows you to modify the length of the cord depending on the mass of what you are slinging, and helps in fine tuning the auto release.  The weight (#1) is free sliding, and you start holding the handle and the pouch (#3).  When you are ready to release, you let go of the pouch, and as it moves away the weight slides down the cord toward the hook (#2).  This automatically releases it.  The timing of the release, as I mentioned earlier, is adjusted by the length of the main cord.  Since the cord is not a set length, nor is it permenately attached to anything, you have the liberty of changing out counter weights if needed for slinging smaller or larger objects.  Sorry if this presentation lacks polish, I'm doing all this on my lunch break, so I don't have a ton of time.  Any thoughts, opinions, or glaring mistakes that I haven't caught?

---

Oh, and did you mention you had a birthday coming up C_A??  ;)

Brian that looks like it could work to me.  I read the thread here and there and it took me awhile to understand what you guys are trying to accomplish with this.  Do you still have to release with a trigger of some kind or does it just release automatically at the apex of the launch?

Could the point between the handle and the booster weight be made semi rigid like a very flexible pole, like a fishing pole or something.  Would this be an improvement or would it be to much like a pole sling.

Asleepundertrees wrote on Nov 13^th, 2008 at 3:57pm:

Brian that looks like it could work to me.  I read the thread here and there and it took me awhile to understand what you guys are trying to accomplish with this.  Do you still have to release with a trigger of some kind or does it just release automatically at the apex of the launch?

You hold the projectile/pouch and do a windup spin with the booster weight. You then let go of the pouch which swings out and the booster weight slides up/out along the lines and triggers the release of the projectile. I think....

Yes, the release is automatic at the apex of the launch.  That is why the length of the cord is adjustable, to fine tune the release point.

Brian

Great command of that paint program, considering the time constraint. You are helping move the compound forward and off the page and into the blue.

Will you need some form of release knot on the pouch and also a way to keep the projectile in place if the pouch is inverted prior to the actual cast?

The sliding weight combined with the outward moving pouch will somewhat lessen the rotation rate of acceleration and the angle between the retention and release components. In spite of this, the cast will get off the line faster.

I think the compound sling as envisioned in this whole thread reminds me of a medium length sling with a shorter sling at the end operated by a midget. Will the two slingers combine to get an average result or will their efforts amount to an effortless cast and a projectile launched into orbit? If it works well, the analogy is something like slinging forward from a car traveling at 50 to 60 mph.

Brian,

May I echo Thomas' compliments on your drawing. I finally understand how the concept is meant to work. (I think.)

Presumably the slinger holds the handle and the loaded pouch at the same time, similar to an atlatlist who hold the dart through finger loops on the actual atlatl. Then the weight is accelerated in the normal slinging manner as if it were the actual pouch and projectile.

Once the pouch/projectile is released the outward moving weight acts like a pulley and causes the pouch to move at twice its own speed until the weight strikes the release toggle. Now the pouch spins around weight much like a whip cracking and sends the projectile out at supersonic speed (hopefully). Theoretically it should work. Please let us know if it does.

Some observations:
1. The weight will probably have to be substantial, so may require several revolutions to get it up to speed.
2. The weight will slow down as it accelerates the pouch/projectile assembly but the energy remaining in it due to its residual velocity will be wasted, ie. ergonomically, the system will be fairly inefficient.
3. Timing the release will be fiendishly difficult; the whole system is rotating as the weight slides down the string, so accuracy will be virtually impossible.

Good Luck,

Aussie

I can partially answer that :-)

1) the whole point is that the large weight does not need to be brought up to much speed - it's just there to store energy. Bear in mind that the original purpose of the sling (as envisaged by me lol) is to throw objects too small to throw easily by hand. it's much easier to put effort into throwing a heavy weight slowly than a smaLL weight very very fast.

the rest is just down to design :-)

Please excuse my brief excursion from the compound over to the same principal applied to my long planned pellet crossbow. Due to other obligations, I’ve kept from starting the crossbow, which I purchased a steel prod for about 2 years ago.

Because of their mass, steel prods of a given draw weight are not as fast as more modern types. The speed increase will come about when the bowstring is released with its lightweight projectile mounted on a small onagerlike sled. When the whole thing strikes a projection at the end, the tiny onager arm will hurl its pellet forward at up to 4 times normal speed. The arm’s overhand swing will be limited by a stop to only 20 deg or so. I like analogies, how about the guy at a fair trying to sledge hammer that metal slider up to ring the bell? This time the sledge hammer is the projection at the end of bowstring/slider travel.    

The tradeoff is the usual 1 ounce projectile will be replaced by a 1 ounce multiplier and a much smaller projectile.

My main goal is keep the medieval style along with the use of small spherical shot instead of bolts (arrows).

Thank all
tom  

Curious Aardvark wrote on Nov 14^th, 2008 at 6:34am:

I can partially answer that :-) 1) the whole point is that the large weight does not need to be brought up to much speed - it's just there to store energy. Bear in mind that the original purpose of the sling (as envisaged by me lol) is to throw objects too small to throw easily by hand. it's much easier to put effort into throwing a heavy weight slowly than a smaLL weight very very fast. the rest is just down to design :-)

Agreed. All slings work on this principle; the pouch rotating on a larger radius moves much faster than the slinger's hand which rotates much closer to the centre of rotation. However conventional slings are not energy storage devices in the way that bows and crossbows are.

The compound sling is really quite different in this respect. The problem is to effectively recover the energy stored in the weight. Similarly to Thomas' crossbow with heavy steel limbs which have high levels of non-recoverable kinetic energy, the weight must be moving for the compound sling to be working. All the energy still in the weight at the instant of the projectiles release will not be transferred to it and in that sense will be wasted. That's not to say it won't work, just that ergonomically it will be inefficient. Steel crossbows from the middle ages were horribly inefficient but they were also very effective.

Quote:

Dale and matthias reckon they got one working - but never took any pics  :(

Matthias does have pictures of his sling and a multiple-exposure shot of him using it (reply #61 in this topic).

Quote:

... Presumably the slinger holds the handle and the loaded pouch at the same time, similar to an atlatlist who hold the dart through finger loops on the actual atlatl. Then the weight is accelerated in the normal slinging manner as if it were the actual pouch and projectile. Once the pouch/projectile is released the outward moving weight acts like a pulley and causes the pouch to move at twice its own speed until the weight strikes the release toggle. Now the pouch spins around weight much like a whip cracking and sends the projectile out at supersonic speed (hopefully). Theoretically it should work. Please let us know if it does. Some observations: 1. The weight will probably have to be substantial, so may require several revolutions to get it up to speed. 2. The weight will slow down as it accelerates the pouch/projectile assembly but the energy remaining in it due to its residual velocity will be wasted, ie. ergonomically, the system will be fairly inefficient. 3. Timing the release will be fiendishly difficult; the whole system is rotating as the weight slides down the string, so accuracy will be virtually impossible. ... The problem is to effectively recover the energy stored in the weight. Similarly to Thomas' crossbow with heavy steel limbs which have high levels of non-recoverable kinetic energy, the weight must be moving for the compound sling to be working. All the energy still in the weight at the instant of the projectiles release will not be transferred to it and in that sense will be wasted. That's not to say it won't work, just that ergonomically it will be inefficient... Aussie

Ludek,

Looks like on the southern hemisphere things go in differnt way ;) On the northen one the "perpetum mobile" actually works :)

There have been said a lot in this thread, so I'm not going to advance arguments for proving it again.

Today (we have first snow) I shot two short movies to ilustrate how sliding mas works in practice. A careful slow motion or frame-by-frame analysis is highly recommended. I wish my camera had a higher frame rate. Because of the frame rate is only 15fs/s the demonstrations were done very slowly. The files are big - 6, 11 Mb.

http://www.kajakowe.com.pl/sling/MVI_9684.AVI

The next moovie seems to be clearer but there was something wrong with the red trigger cord that pulled the retaining cord.

http://www.kajakowe.com.pl/sling/MVI_9685.AVI

Jurek

Greetings Jurek,

Great to hear from you! It's been some time.

With only dial-up so large a file will take a while to download. I may be able to see it at the library.

I'm glad the project worked, if my reservations proved groundless then fine as well.

So the question remains, does the additional complication translate into enough improvement in release velocity and how hard is it to control?

Jurek

The full screen video was very clear and your setup made the demo easy to understand. The idea for an armless trebuchet was quickly visualized, but not its advantages.

tom

Ludek, Thomas,

Ludek, your reservations were as "grounless" as my idea of sliding mass was. Though my limited experience with the rather rough compound sling seems to prove the idea, not mentioning Matthias' computer simulations and tests with a real sling.


Quote:

...The idea for an armless trebuchet was quickly visualized, but not its advantages...

All depends of what adventage is considered. I have no doubs that a compound sling would be much more awkward and impractical in everyday use, targets sports, hunting etc. Its complication needs more advanced technology for more efficient action. A good design will probably need a bearing pulley connected with the mass, sophsticated design of very precise and light trigger, puch (or something like that)... Better matherials should be used either, lenghts and masses adjusted.  However it all isn't able to gurantee that the device will be practical for the mentioned activities. So considering more advaced designs, a bow, crosbow or even firearm seem to be a better choise. Well, I still prefere the coventional simple sling.

Anyway, the main question in this thread was about if additional mass gives adventage with regard to muzzle velocity and if the sliding mass is able to transfer energy to a lightweight projectile efficiently in order accelerate it much more. The discussion was rather about prnciples.

Thomas, please compare carefully (in very slow motion) the maximum velocty of the sliding mass just before the release of the pouch with the velocity of the released snowball, you probably will notice the difference.


Quote:

...So the question remains, does the additional complication translate into enough improvement in release velocity and how hard is it to control?

It is actually more difficult to control the projectaile release, but still possible if we are not talkig about target slinging. Timing is different than in convential slinging. It is mainly because the projectile release is a bit delayed - there are two stages of the lash, or rather two lashes. The first one is similar like in normal slinging, ended by the pouch relesae (from the palm), the socond one is not controlled by slinger, short and rapid like hell, ended by automatic release of the projectile. Precision of the first release depends of slinger, the second one depends on precision of adjustment of the trigger and (i suppose) on random orientation of the pouch.

Hence you have to change your habits (it isn't easy) and start the stroke a bit sooner. How it works in practice you can on the new movies I made today.

Consider that the used projectile is very soft and light (<<20 grams) ball, that is a toy for cats. Although it lose its velocity very quickly because of air drag an its small mass, the energy of impacts is still very impressive.

BTW the multiple rotations are done only for feeling.

http://www.kajakowe.com.pl/sling/MVI_9693.AVI


http://www.kajakowe.com.pl/sling/MVI_9695.AVI


Greetings,

Jurek

Good to see you back Jurek.

I see that the ball left a mark on the wall in the second clip. Certainly looks pretty impressive. Do you have any estimate of the speed?

Jurek

I ran the frame by frame and slow motion the first time I saw the video and noticed the dramatic speed increase.

My comment about the trebuchet was not directed to your slinging demo per say but to the moving pulley mass as applied to a siege weapon application of this general principal. However, I can not imagine an armless trebuchet with a vertical falling weight and pulley mechanism being very efficient.

tom    

Wanderer,

Thank you, your feedback is much appreciated.


A precise estimation is difficult, because the final release (the last movie) was somewhere between the last frame (A) which is showing the ball in the palm and the next one (B) showing the ball in fly.

We can see that the time from the frame (A) to the impact is ca. "two frames", it means
2*1/15 s = 1.33 s.    (15 frames/s)

The distance to the gate was at least 10 m, I think. At my gues time from the {A} to final release of the ball from pouch was ca. 0.3 s.

So the time from the release to the impact:

T = 0.133 - 0.03 = 0.1 s

What gives the average velocity:

V = 10/0.1 = 100 m/s = 360 km/h = 224 mile/h

I felt the shot as very vibrant indeed, but I can't really say how the result differs from the reality. I have also no idea what was the muzzle velocity. The used ball is ligher and softer than a stress ball (BTW excelent ammo for indoor practice) so its velocity was decreasing rapidly. I even imagine that it was somewhat flattened on the begining of its fly due to air drag.

Jurek

Jurek

I used a miniature digital sound recorder and the Audacity sound program to get an interval of .158 sec for the third video based on the snap of the sling versus the ball impact. Then I assumed a distance to the slinger of 5 m.
This was subtracted from a total of 15 m to the wall to allow for the speed of sound.

.158 sec /10 m = .0158 preliminary interval for 1m
1/.0158 sec = 63.29 m/sec
15-5 =10m = distance traversed by sound to be deducted
335 m/sec = speed of sound
10/335= .0299 sec = interval to be deducted

.158-.0299 = .125 sec = corrected interval
.125 sec /10m = .0125 = interval for 1m
1/ .0125= 80 m/sec

tom  

Hells teeth, that's fast!

Jurek and Thomas,

That's nice work! Given the uncertainties the two estimates seem pretty close - and frighteningly fast. If I had anywhere I could sling with a 360 degree safety zone (which I would need) I'd be inspired - again.

Hmm... just thought that if you can pick up the echo of the whip crack from the wall you could measure that distance as well.

The idea that you guys turn such a primitive device into
a totally mathematical and graphic, is just plain exelent.

Some approximations on energy with typical projectile masses and velocities from compound and conventional slings:

(Formula: KE = 1/2 m x v^2)

Compound sling:      
Mass of projecile = 20 g   Velocity = 100 m/s   KE = 100.0 J

Conventional sling:
Mass of projectile = 75 g   Velocity = 52 m/s    KE = 101.4 J

The smaller projectile travelling at almost twice the speed has very close to the same energy as the conventionally powered larger but slower moving one.

Yurek wrote on Nov 25^th, 2008 at 2:34pm:

... We can see that the time from the frame (A) to the impact is ca. "two frames", it means 2*1/15 s = 1.33 s.    (15 frames/s) The distance to the gate was at least 10 m, I think. At my gues time from the {A} to final release of the ball from pouch was ca. 0.3 s. So the time from the release to the impact: T = 0.133 - 0.03 = 0.1 s What gives the average velocity: V = 10/0.1 = 100 m/s = 360 km/h = 224 mile/h ...

I just relezed that I had made a mistake in the calculations. Alas, the true is less impressive. I took wrong frame rate for them. My camera catches the 15 fms/s only for resolution 320 x 240, but I used the 640 x 480. In this case it gives only 10 fms/s, really poor rate.


Then the calculations (for the last video) should look like this:

We can see that the time from the frame (A) to the impact is ca. "two frames", it means
2*1/10 s = 0.2 s.    (10 frames/s)

The distance to the gate was at least 10 m, I think. At my gues time from the {A} to final release of the ball from pouch was ca. 0.045 s (I increassed it from the 0.03, because before I estimated it as a part of the frame interval 1/15 s.).

So the time from the release to the impact:

T = 0.2 - 0.045 = 0.155 s

What gives the average velocity:

V = 10/0.155 = 64.5 m/s = 232 km/h = 144 miles/h  (10 m ???)


Anyway, still impressive result considering that the ball was ultra light and soft. I'm pretty sure the result is impossible with a common sling and that kind of projectile.



Tom,

Thank you for the neat calculations. Yesterday I used VirtualDub to separate the soundtrack from the last video. Then, after removing noises I measured the time between the snap and the impact on the gate using Audacity. The time was 0.19 s.

http://www.kajakowe.com.pl/sling/audacity.jpg

Sound lag from the release point to the camera:      5 m/335 m/s = 0.015 s
Sound lag from the impact point to the camera:      15 m/335 m/s = 0.045 s

Then the corrected interval is:         0.19 s + 0.015 s - 0.045 s = 0.16 s

Then the average velocity is:      

V = 10 m / 0.16 s = 63 m/s = 227 km/h = 141 miles/h

The result is very similar to the above one. However they both are still disputable because of the estimated distances. I'm going to verify them as soon I get an occasion.

Yurek

I used the first video in the second group of 2 for your average of 80m/sec which included the deduction of e.t. between the two sound sources.

http://www.kajakowe.com.pl/sling/MVI_9693.AVI

Your efforts are greatly appreciated by all of us, thank you.


tom  

YESSSSS !
proper video of a working compound sling :-)

Major kudos to yurek !


Quote:

The smaller projectile travelling at almost twice the speed has very close to the same energy as the conventionally powered larger but slower moving one.

Which was my original idea :-)

Okay now yurek's got one that works - any chance of plans or a buildalong yurek ? Pretty please.
What you have there looks perfect for 50 calibre paintballs, which is what started this rollercoaster of a journey in the first place lol.  

You guys are amazing.

So, I've also got this idea for a perputual motion engine....

This isn't an engine,but it sure is cool.

http://www.youtube.com/watch?v=us7YB7eiOeQ

Yurek,

could you please post a picture of your sling?
I don't understand the release mechanism

Thanks

Using the weaver/figure 8 release, a compound sling without a sheathing tube could work. I haven't read through the whole thread so I may repeat someone. With LONG cords folded over twice and strands splitting off of the release and retention cords about a third of the distance from the pouch, a short grip can be maintained. Also and trilateral pouch proves both good grip and good release for the projectile. Using this configuration the booster/ballast doubles as the projectile. Four cords are in the hand at the beginning of the throw, but on the second loop around the two strand from the middle of the retention and release cords would need to be released. The length of the sling triples, and on the third loop around (or the end of the second) the actual release cord is let go and the projectile leaves with triple the momentum as with a normal sling. I'll post pics later. I just need a little help with the posting pics part. Sorry for being such a n00b!

wow, fascinating idea! :o i have tried the link-http://www.kajakowe.com.pl/sling/MVI_9693.AVI but it does not work, anyone direct me to one that does? Thank you!

Yeah,those videos are gone :(

Would be great to see them! I have actually had this thread saved in my favourties for some time now, its a concept that really interests me. It really is the biggest modern step forward in sling design it looks to me, and it would be great if we could get some use out of it.

(Also the concept of throwing further always interests me :P)

Nemo

Masiakasaurus wrote on Jan 26^th, 2009 at 10:44am:

Using the weaver/figure 8 release, a compound sling without a sheathing tube could work. I haven't read through the whole thread so I may repeat someone. With LONG cords folded over twice and strands splitting off of the release and retention cords about a third of the distance from the pouch, a short grip can be maintained. Also and trilateral pouch proves both good grip and good release for the projectile. Using this configuration the booster/ballast doubles as the projectile. Four cords are in the hand at the beginning of the throw, but on the second loop around the two strand from the middle of the retention and release cords would need to be released. The length of the sling triples, and on the third loop around (or the end of the second) the actual release cord is let go and the projectile leaves with triple the momentum as with a normal sling. I'll post pics later. I just need a little help with the posting pics part. Sorry for being such a n00b!

It's kinda weird reading a thread where the only member u know is CA. and your post is erally the first one I've mostly understood. Pics would be great!

Knowing what I do now, I think my idea would only work with a helicopter or pirouette throw and would be severely limited by drag on the cords. That's why I never got pictures up, I was wrong. Matthias and Yurek had great ideas, though.

nemo wrote on Feb 17^th, 2012 at 8:35am:

Would be great to see them! I have actually had this thread saved in my favourties for some time now, its a concept that really interests me. It really is the biggest modern step forward in sling design it looks to me, and it would be great if we could get some use out of it. (Also the concept of throwing further always interests me :P) Nemo

There are actually some major advances that have been made and shared here on this forum,most members just choose to ignore them and continue to produce museum type replicas.

 Brett

I'm relatively new here and haven't been able to read through everything so new sling technologies are definately an eye catcher. I would be interested in seeing those modern advances. I like this thread but haven't seen any pictures of finished products. You're right Jax. For the most part we're just replicating museum pieces where the only thing that has significantly changed is the materials being used. Where are these technological advances in slinging?

Off topic replies have been moved to This Thread

A lot of the pictures have been taken down from their original hosts or the links have been moved, but there are a few on the thread. http://slinging.org/forum/YaBB.pl?num=1174772635/60#61

As for the technological advances in slinging, they mostly happened early in development. People started carving sling stones instead of having to hunt for naturally round ones. Somewhere down the line, military slingers switched to cast lead bullets for greater range and damage. Someone in the Persian army came up with a way to sling darts. Other than the shape of the glans and the materials the sling and glans are made from there's little in slinging that can easily be improved. Look at the advances in sports between ancient times and now. A long time ago people used sewn up animal skins (or organs) as balls and nowadays we use... more perfectly shaped animal skins as balls. There are now balls made from plastic and rubber and balls with a high level of precision in their shape, but for most purposes sewn up leather is still in use.

Wow that was a great anology! So they technological andvances in slinging weren't so much in the slings but in the ammo! Man, common sense can take you a long way, good post.

Masiakasaurus wrote on Feb 20^th, 2012 at 6:50pm:

A lot of the pictures have been taken down from their original hosts or the links have been moved, but there are a few on the thread. http://slinging.org/forum/YaBB.pl?num=1174772635/60#61 As for the technological advances in slinging, they mostly happened early in development. People started carving sling stones instead of having to hunt for naturally round ones. Somewhere down the line, military slingers switched to cast lead bullets for greater range and damage. Someone in the Persian army came up with a way to sling darts. Other than the shape of the glans and the materials the sling and glans are made from there's little in slinging that can easily be improved. Look at the advances in sports between ancient times and now. A long time ago people used sewn up animal skins (or organs) as balls and nowadays we use... more perfectly shaped animal skins as balls. There are now balls made from plastic and rubber and balls with a high level of precision in their shape, but for most purposes sewn up leather is still in use.

 Masi, and why are you linking back to the thread you are replying to?

 All of this braiding and topics about zombies has more than a few people confused.We have a body of work in previous threads,do we need a sticky suggestion topic?

Brett

I linked to the one post with pictures so that Pikaru can see the fruits of our labors. He said that he hadn't yet seen a picture of a finished product.

What kind of sticky suggestion topic are you talking about and why?

someone PLEASE MAKE ME ONE !

Matthias seems to have dropped off the planet (possibly almost literally as he was spending time at the tip of south america before he stopped posting).

I'll swap stuff, give you stuff - I don't care, I just want one of these !
It was my idea after all lol
I just wanted something to sling paintballs with and this seemed like the way to go.

Hell I might even get desperate enough to try and make one myself - and that could be bloody dangerous :-)  

Unfortunately all old binaries I have posted to the forum are gone. Some of them I lost either. Maybe someone saved my videos showing the compound sling in work and still keeps them somewhere? Maybe Thomas, as he analyzed them with Audacity? If so I would repost them.

I'll show you what I've been working on to improve on Brian's ideas, but it may take me some time. After a long, hard day modeling and drafting parts it's hard to drum up the enthusiasm to draft a sling. When I have time, I'll try to remember to make cardboard mock ups for you instead. For reference, here's Brian's picture:
http://slinging.org/forum/yabbfiles/Attachments/compound_sling_001.bmp
The hook should have a 2 point attachment on the end nearest the ballast for stability, the pouch should have a securing mechanism to prevent spilling your ammo, and the ballast should be replaceable to adjust the sling to different levels of resistance. I can make the pouch to show you what I intend, but I need to do some more thinking on the ballast issue and I CAN make a picture to show what I mean about a 2 point attachment. In the picture below (which I shamelessly modified from Brian's very clear picture, and do not own the rights to ;)) the red line is where I would add another piece of string. This would provide a consistent angle of release for the sling, add to the triggered release, and provide a way to slow down the booster even further and prevent any damage to the hook. The section of cord that I colored blue should be either replaced with a stick or sheathed in a rigid tube, which would help my modified automatic release to be more effective.
http://i1133.photobucket.com/albums/m595/masiaka/compound_sling_003.jpg

 I see!I sent my dad a message,he probably has the video on his hard drive,we'll see.

 Brett

wrote on Feb 23^rd, 2012 at 9:07am:

I see!I sent my dad a message,he probably has the video on his hard drive,we'll see.  Brett

Thank you, Brett.

I no longer have this video or the Audacity speed recording. The compound bow has made archery more user friendly. Will this happen with a compound sling?  

Thomas wrote on Feb 23^rd, 2012 at 2:42pm:

I no longer have this video or the Audacity speed recording. The compound bow has made archery more user friendly. Will this happen with a compound sling?

The release would probably be earlier, by a lot. It might feel a little unnatural- to anyone, not just a slinger trained in a normal sling. The area where the sling is released and the cords opened up is very similar to when a baseball pitcher lets go of the ball. With the compound sling, the release will be out of sync with regular throwing abilities.

*BUMP*

I've started to 3D model my compound sling during my down time at work. In a few week I should be able to present it as a downloadable .PDF.

I've read this thread briefly..you've got a volunteer.So IF some of you,who are more into this project would give me a brief summary of the progress,i'm willing to cast a lead booster of a weight that's highly promissing to work,and cord lengths,and releases that might work,and i'll make it and try it out. If we share the work and ideas,we'll progress faster than a single slinger,ya'll know that. ;)
Jurek,i read that you've made a prototype of this sling..enlighten me,please! :D

I know dale and matthias made them succesfully - no idea yurek had as well :-)

I want one soo bad  ;D

Is Dale still a member? I have seen matthias around here..not sure though...it would be nice to rotate a canonball slowly,then with the pull of trigger a WHOOOOSH CRACCKK and the projectile shoots of like a bullet.Also carrying more lighter ammo and a heavy sling might be more practical ,depending on the exact successful products details.
Probably it wouldn't replace my olskool slings,even if it would work fairly good,but could be much fun ;)

Masiakasaurus wrote on Feb 22^nd, 2012 at 10:11pm:

I'll show you what I've been working on to improve on Brian's ideas, but it may take me some time. After a long, hard day modeling and drafting parts it's hard to drum up the enthusiasm to draft a sling. When I have time, I'll try to remember to make cardboard mock ups for you instead. For reference, here's Brian's picture: http://slinging.org/forum/yabbfiles/Attachments/compound_sling_001.bmp The hook should have a 2 point attachment on the end nearest the ballast for stability, the pouch should have a securing mechanism to prevent spilling your ammo, and the ballast should be replaceable to adjust the sling to different levels of resistance. I can make the pouch to show you what I intend, but I need to do some more thinking on the ballast issue and I CAN make a picture to show what I mean about a 2 point attachment. In the picture below (which I shamelessly modified from Brian's very clear picture, and do not own the rights to ;)) the red line is where I would add another piece of string. This would provide a consistent angle of release for the sling, add to the triggered release, and provide a way to slow down the booster even further and prevent any damage to the hook. The section of cord that I colored blue should be either replaced with a stick or sheathed in a rigid tube, which would help my modified automatic release to be more effective. http://i1133.photobucket.com/albums/m595/masiaka/compound_sling_003.jpg

I like the idea of the cord to stabilize the hook, and a replaceable ballast would be very useful...I haven't thought about this in a while, I'll have to do some more work on it!

Brian

a 300g booster seems to be a good weight to a folded 1m compound sling.Whatcha think? Also that automatic release seems to me that could have problems not releasing,or releasing at the slightest slack of the cord. Of course it would have to be adjusted,but still..the biggest problem with this whole compound sling would be an automatic release,the rest is a piece of cake(finding the ammo booster weight ratio for ideal energy transfer)

I've just come from theHURL.org where I was reading about a trebuchet using this two-stage compound sling.
The high school team has a successful model based on Matthias' theory.

As for usage in a hand sling, I have a hard time seeing how a 2/3 Lb (33g) booster would have enough mass to assist throwing a projectile of 1/2 Lbs. (200g or 8oz). As with a normal trebuchet, the out-swing of the projectile creates a centrifugal effect pulling against the forward motion of the Booster. I don't think that booster has enough mass to inertia it's way through the back pull and will stop swinging somewhere over the users head.

The concept is fascinating
I think I will do some experimenting with a weighted poll sling. Something like having a slip pin on a sledge hammer.

Who would want a 300g booster with a 200g projectile? that's 500g+ ,it would be heavy and very inefficient. A 300g booster and a 50g projectile would be much more suitable. Although the ideal weights and their ratios will have to be tested.
Chuck,what weights were those guys using,and with what degree of success?

jlasud wrote on Jul 22^nd, 2012 at 8:20am:

Who would want a 300g booster with a 200g projectile? that's 500g+ ,it would be heavy and very inefficient. A 300g booster and a 50g projectile would be much more suitable. Although the ideal weights and their ratios will have to be tested. Chuck,what weights were those guys using,and with what degree of success?

Sorry, I don't have that data yet but I'll presume that they are aiming toward hurling a 10Lb pumpkin.

I realize that not everyone uses a hand sling for massive projectiles like I do but I guess I just don't know how much weight is considered standard by our slinging community. Right now I'm throwing wild Florida grapefruit, average weight about 2-Lbs estimated. Given an extrapolated booster weight of "way-too-much", I don't think I could handle it.
I have done cantalopes which weigh around 4-Lbs but they almost rip my arms off. I'm getting too old for that.

I came to this party late.  A few pages back there were several links to a video of a working model of this 'compound sling' but the none of the links work for me.  They all lead to a 404 error 'page not found'?  Is there anyplace else that the video's are still available?

I'm also curious how the release issue was solved to allow controlled release at just the right point in the compound arc?

-Modified: Never mind on the release I found links to the pictures... but still no video.

-namuh1

ChuckRocks wrote on Jul 22^nd, 2012 at 9:24am:

jlasud wrote on Jul 22nd, 2012 at 8:20am: Who would want a 300g booster with a 200g projectile? that's 500g+ ,it would be heavy and very inefficient. A 300g booster and a 50g projectile would be much more suitable. Although the ideal weights and their ratios will have to be tested. Chuck,what weights were those guys using,and with what degree of success? Sorry, I don't have that data yet but I'll presume that they are aiming toward hurling a 10Lb pumpkin. I realize that not everyone uses a hand sling for massive projectiles like I do but I guess I just don't know how much weight is considered standard by our slinging community. Right now I'm throwing wild Florida grapefruit, average weight about 2-Lbs estimated. Given an extrapolated booster weight of "way-too-much", I don't think I could handle it. I have done cantalopes which weigh around 4-Lbs but they almost rip my arms off. I'm getting too old for that.

The point of the compound sling would be to use the KE of a heavy booster to propel a lightweight projectile at very high speeds,unattainable with a conventional sling. For most of us one pound is about the max weight we would want to rotate around. Around 4 oz is the most popular,average ,conventional sling ammo weight for most of us.

I noticed that in the photos and posts that I was able to read the release was 'automatic' by virtue of the energy storage weight sliding to hit a release hook at the apex of the arc of the secondary pouch.  I read a lot about needing to tune this to release at the right place.  It seems that this would make accuracy very challenging  since the release could not be 'adjusted' in realtime for variations in the spin up by the thrower.  I haven't tried any of this obviously and since I'm so new to this sport, I hope not to sound off and offend anyone, but may I suggest an alternate that might give control to the release.

Attach a second string to the sliding weight and adjust the length so the weight is restrained only a fraction of an inch from the release hook.  The separation would have to be enough to ensure that the weight didn't hit the hook prematurely due to stretch of the restraining cord.  The other end of the restraining cord would be knotted and held in the fingers just like the release side of a conventional sling.  When the thrower times his/her throw and senses the pouch reaching the chosen release point the secondary restraint/release cord is released and the weight slides the fraction of an inch and releases the actual release cord of the pouch.

It might take some getting used to the lag from the release of the restraint cord to the release of the actual pouch release cord but I think it would not be much different from the lag in the firing of a flintlock rifle in compensating for the pan flash to actual ignition... something every flintlock shooter does in shooting at a moving target.  

If this is an unworkable suggestion, for some reason I haven't seen in my brief time looking at this problem please forgive my intrusion, but my first career was as a theoretical physicist and I'm fascinated by these kind of problems.

-namuh1

Modified: After looking deeper I'm afraid it would not work :(

Your analysis is fairly close about having little control over the ballast, but it does not affect the point that the sling releases at very much. The hook automatically releases at the same spot on every throw the same way a staff sling does. This is adjusted by changing the length of one sling cord in relation to the other. The sliding ballast only adjusts the length of the second sling, which increases the angular velocity at the end of the second sling, making it move faster. It's possible to make a compound sling with a fixed ballast, but it will be less efficient at transferring energy from the ballast to the projectile. The sliding of the ballast is the way that the compound sling's designers chose to throw small, light projectiles with the speed that they could a larger projectile. By the time the ballast hits the hook the sling will have already released, though it needs to be tuned a little so that the ballast will have transferred as much energy to the projectile as possible (which will happen close to, but not during impact with the hook since that can decrease accuracy). Attaching a string to the ballast is not a ideal solution for this because it bleeds energy from the ballast. Given that primer, welcome aboard! As you can see, this is a complex task and we can use all the help we can get!

Your explanation is precisely the conclusion I reached after opening my mouth when I shouldn't have.  At first glance I didn't think about the fact that the ballast is released when the pouch is released.  I was only thinking about the release of the secondary.  After further observation, I saw that the real impulse of energy came from the sliding of the ballast in much larger ratio than it's presence in the first place... exactly as you recounted.  I'm not sure that I follow your comment that the hook will have already released by the time the ballast hits the hook?  I'll have to make some calculations regarding the event before I make any more mistakes but this is one of the most fascinating problems in multiple body motion I've encountered, not to mention the fun of making one of these things and getting it to work!

-namuh1

jlasud wrote on Jul 22^nd, 2012 at 10:17am:

ChuckRocks wrote on Jul 22nd, 2012 at 9:24am: jlasud wrote on Jul 22nd, 2012 at 8:20am: Who would want a 300g booster with a 200g projectile? that's 500g+ ,it would be heavy and very inefficient. A 300g booster and a 50g projectile would be much more suitable. Although the ideal weights and their ratios will have to be tested. Chuck,what weights were those guys using,and with what degree of success? Sorry, I don't have that data yet but I'll presume that they are aiming toward hurling a 10Lb pumpkin. I realize that not everyone uses a hand sling for massive projectiles like I do but I guess I just don't know how much weight is considered standard by our slinging community. Right now I'm throwing wild Florida grapefruit, average weight about 2-Lbs estimated. Given an extrapolated booster weight of "way-too-much", I don't think I could handle it. I have done cantalopes which weigh around 4-Lbs but they almost rip my arms off. I'm getting too old for that. The point of the compound sling would be to use the KE of a heavy booster to propel a lightweight projectile at very high speeds,unattainable with a conventional sling. For most of us one pound is about the max weight we would want to rotate around. Around 4 oz is the most popular,average ,conventional sling ammo weight for most of us.

Thanks Jlasud,
Now, did I miss the explanation for how the design overcomes centrifugal retardation of the booster?
I beleave the booster concept can be made to work on a trebuchet but I strongly doubt it working for a hand sling without a whole lot of tweeking and perfect repitition of motion by the slinger.

Also, why would anyone want to sling anything small? Who slings BBs?

---

  Great idea.  I don't know if this has anything to do with it, but I have made and seen bullroarers on the end of a pole, you don't swing the pole but you kind of rotate it in a sort of butter churning motion, it works kind of the way a screwdriver works increasing the torque with a longer handle.  A bullroarer on the on the end of a stick needs only a very short cord to make it work but it needs a long one without it.  I suppose you could try the same thing with a sling and there would be different ways to release it, including a hook that it slips off when you tilt it or run the cord through a ring down to the hand hold and let go of it.

So let me get this straight. The counterweight takes the place of the normal pouch, and the loaded pouch takes the place of the release cord.

when you wind up, W accelerates up to normal sling speeds. As you release, first R2 opens up and extends at close to speed of sound velocities (what normally makes a crack), then RL opens, and the stone inside is released at much higher velocities as normal. W must be pretty heavy to be able to generate the speed needed for RL+ammo to open at high speeds.

My thought is that rather than having a pouch, a slip knot or something of the sort could be used instead. The loop would be very wide to safely hold a stone, while the running end would be anchored on R1, similar to a captive release sling. On release, when R1 and R2 attempt to separate and open up, R1 (anchored to the slip knot) would yank on the running end and release the knot, allowing the stone to fly free. The knot end would have to have enough slack to allow the sling to open fully and gain max speed before going taut and yanking the sling open. It would also have to undo itself in a way where it doesn't get in the way of the stones release, so that accuracy isn't affected too much.

I would think that something like a grapeshot sling, with one end covered with a flap would be the best, only that the flap could only be opened when yanked on. This would allow for the smoothest opening. Rather than using a bottle or can, you'd have to use an actual bag like thing, that would be just large enough to hold things in place (so that it wouldn't get in the way too much, and still go fast enough). I would think the ammo would best be something like 1/2 inch steel ball, or small pebble. It would be light enough to go at optimum speed, assuming W is heavy enough. It should be something that someone could normally pick up off the ground, maintaining the slings versatility (two big words [for me] in one sentence while out of an essay, wow).

BUT: by having the easy release system you wouldn't have to deal with the added bulk of RL.

The release has to be infinitely reusable until worn through too, once again still being as versatile as a normal sling. It might be easier to have the ammo held onto RL by a thin strand of something that will break as soon as the sling hits a high speed, but it will be very slow to reload, slightly less safe, and not as self sustaining.

My best guess for pouch is a circle with very shallow cupping, so that when a 1/2 in steel ball is placed in it, 1/3 of it is covered. There would be slits on the edge of the pouch for a wide strap to pass through. This would face outward and would hold the steel ball in place. One end of the strap should taper and be attached to R1, the other should be held in one of the slits in the pouch by friction or something that would give when yanked on.

Am I even close to what the original purpose of the compound sling is? This is just based on the OP and Masi's diagram.

---

I'm not exactly sure I understand your proposal about a slip knot, kid.

To answer your question, the original purpose of the compound sling was to sling lighter weight projectiles with a higher speed than is normally possible with a sling. Potential Energy is stored in the ballast and transferred to the projectile as Kinetic Energy during the second, automatic release. The compound sling works just like a staff sling at the moment of release, but the complicated booster mass mechanism makes it so that the second sling moves faster than a staff sling ever could.

C_A did a great job of explaining the benefits, and operating principles of the compound sling.

Curious Aardvark wrote on Mar 25^th, 2007 at 8:30am:

Not so adaxl the enrgy you put into the booster mass is converted directly into the missile via the longer cord. What it should allow you to do (if correctly made and working) is to put a lot more strength into the throw itself. The heavier the missie in a normal sling the harder you can pull against it without straining your own muscles (it's like throwing a punch and missing, the hader you punch the more you hurt yourself when you miss). The problem with a conventional sling is that sure you can use heavier ammo and up to a point you will get more distance. But at a certain weight your own strength will start to tell against you and the velocity will drop - even if you are putting more effort into the throw. With this method you can put a lot of effort into a fairly slow throw which is then directly converted into a much faster throw with a lighter missile. If it helps, think of it as gearing. High gearing on a bike lets you push really hard and pedal slowly but the wheels go round faster than low gearing where you pedal faster but with less effort and the wheels go round proportionally slower.

Curious Aardvark wrote on Mar 27^th, 2007 at 6:02am:

Ah ha finally a bit I can answer again lol Forget the maths and the mechanics - don't have the inclination to tackle those, but I do actually understand the principle involved and for me jureks drawing makes things perfectly clear. And I do know about the physiology :-) Funslinger The main reason we get sore joints when attempting to sling missiles - literally - out of sight,  is that we are moving our joints as fast as we can to transfer that speed into the sling. And to a certain extent even with a reasonable weight missile we're still putting in a lot more effort than can be efficiently translated into the missile (we're back to the punching and missing again). This method relies on the slower application of force. It's like picking something fairly light up from the ground and doing so as fast as you can. Very easy to bugger your back up. If you pick something much heavier up with a more measured lift, your body will be working more efficiently and less likely to cause problems. This compound sling works on the same principle. You are expending the same amount of energy, but in a more controlled and efficient manner. Also you are using a much longer release cord - so effectively, if it works, you can sling with a 6 foot sling while retainng the velocity that you can manually impart to a 3 foot sling. The impact on the slingers body should be less because your muscles are working more in harmony and with greater efficiency.   :-) I do have to say matthias that yureks design [sliding booster mass] does look a lot more elegant than yours sounds ;-)

ChuckRocks wrote on Jul 22^nd, 2012 at 7:10pm:

Thanks Jlasud, Now, did I miss the explanation for how the design overcomes centrifugal retardation of the booster? I beleave the booster concept can be made to work on a trebuchet but I strongly doubt it working for a hand sling without a whole lot of tweeking and perfect repitition of motion by the slinger. Also, why would anyone want to sling anything small? Who slings BBs?

I undrstand the overall concept but,i'm not far beyond that,for me actual prototypes would tell me what's up.For now i'm too busy to start working on this.
Some of us would rather see a 50g lead,or stone projectile flying at 150 m\s, than a 5 pound rock at 15 m\s,me included, also you can carry more 50g ammo,and sling farther than 5 pound ones,and they would be extremely powerful.
Sort of like how medieval handguns used  1" lead balls and today's handguns use tiny bullets that are much faster and more efficient.
I could have hired you to sling big stones to build my houses foundation :D

I'm working on the mechanics to understand what's going on here. For the sake of endless repetition I see the breakdown this way:

With a static ballast, i.e. one that is fixed and does not slide, the effect is like an inefficient staff sling.  Why? Because the ballast is not transferring its energy to anything but simply acting as a 'stabilizer' against which the secondary retaining string rotates.  Without the ballast in this configuration the rotational energy imparted to the pouch at the end of the secondary retainer would be absorbed by flexion in the primary string thus subtracting from the transfer of energy that a stiff staff would impart.  With the ballast and to the degree that the ballast resists flexion in the primary string because of its mass, the system works like a staff sling where the transfer of energy is increased only because of the longer moment arm created by the primary string added to the slingers arm.

Since this whole problem is about rotational velocity:

The sliding ballast system works in a very very different manner.  Here the ballast actually does store energy that is transferred to the pouch on release of the pouch from the hand.  It does so because it 'effectively' pulls the secondary retention string shorter as it slides out to the end of its travel as the pouch at the end of the secondary retention string (along which the ballast is sliding) spins up around the center of mass of the ballast.  This is conservation of momentum of the pouch which is seen every day in school yards.  On the spinning platforms that the kids push into circular motion and then jump on the kids can substantially increase the rotational velocity by moving their bodies closer to the center of the spinning platform.  It may seem backwards to the spinning pouch but it is the same mechanically.  As the radius of the secondary retaining string is shortened by the sliding ballast, the momentum of the pouch is kept constant by the pouch increasing it rotational velocity exactly as the originators of this design wanted.  You can test this simply by tying a rock to a string and passing the string through a sewing thimble.  Then whirl the string/rock combination over your head helicopter style but by holding the thimble as the center of rotation and the end of the string in the other hand to keep it from flying off.  Then while the rock is spinning around, pull the string shorter through the thimble and observe that the rock moves faster the shorter you pull the string.  You will also feel why the mass of the ballast is important because your hand holding the thimble will feel quite some force to resist being pulled out of line as you shorten the string through it.

In truth, this is a simplification of the real problem.  For example there are second order effects that do contribute to the problem.  The fixed ballast does, in fact, interact to some degree with the energy given to the pouch because its mass must resist, by inertia, being displaced by the rotating mass of the pouch pulling on it, but I believe that this is a second order effect and contributes little to (and may even detract from) the pouches energy compared to the increase in moment arm achieved by the long strings.  This would be a terrific problem to assign to a graduate physics class in mechanics, better even than the classic dragster problem.

My skill with differential equations is 40 years old so I've asked a friend, more competent than I am, to work out the actual mechanics so I'm hoping to have a more complete and accurate description of the problem in a few weeks.  In the meantime, I've GOT to try making one of these things!

How it works: (primative version)

Earth swings around Sun.
Moon swings around Earth.
At farthest point from Sun, Moon is moving through space faster than the Earth.
At that point, Earth lets gravity slip and away goes the moon.
Oh well!

But in order to optimise moon's speed, we will tuck her down next to the Earth's string from the Sun and allow moon to swing out at the apropriate time to accelerate the rate of acceleration.

This method of projectile tucking is currently used by several pumpkin hurling trebuchet, particularry those of the Whipper design.
This http://www.youtube.com/watch?v=zrsz5P3Sjkg link will take you to You Tube for a demo video.
If it's too fast, please wait, the slow-mo and quad-slow-mo will follow.
Please note the pumpkin is held to the arm atthe start of the firing sequence.

Vedio credits: Trebuchet: NASAW by Team Urban Siege, Video recorded by "Craig Basement", edited by myself.

:o WOW...I wonder if the thorus spiral has anything to do with it's mechanics. :-? But sure it looks efficient!

brilliant - yep that's what the compound sling does :-)

Made a prototype,tried it,not satisfied. It's 85cm long folded,300 gram booster.
I tried it with light and mid weight ammo ~ 40g-120g and shot more than a dozen shots,for some i used much power,still i felt like it was like a not so powerful regular sling throw. Overall it performed like a regular sling in that length. There could be a better weight,length ratio,but this one is not worth it,but i HAD to try it. It felt like the booster compensates for the slow windup due to heavy weight. One thing is sure: the booster ain't transferring efficiently it's energy into the projectile. Maybe a lighter booster would be better..not sure though.
A high speed camera would be a must to see what's actually happening,and how could it be improved.
The automatic release worked perfectly.Only once it did not release,and it was because the temporary hemp trigger cord got untied of the release hook,and at that throw i could feel the booster hitting the stopping knot,and it pulled on my arm.Didn't felt that during normal throws,so i guess it was working in some way..

---

So from the photo is it correct that the white cord causes the release as the secondary spins out around the weight, but also the weight is free to move so the secondary is becoming shorter as it rotates out into line with the primary?

-namuh1

namuh1 wrote on Aug 4^th, 2012 at 5:14pm:

So from the photo is it correct that the white cord causes the release as the secondary spins out around the weight, but also the weight is free to move so the secondary is becoming shorter as it rotates out into line with the primary? -namuh1

Yes,the white,hemp cord pulls on the release hook,as the blue line almost straightens up.And yes the secondary shortens as the booster slides outwards,until it hits the knot just below the release hook.

C_A!!!!
In my waking up stage,sometimes really good solutions come to my mind :)
It's a bit different,than the previous designs but it CAN work,and probably quite good,and it's simple.
You make a whip,probably a short one, 1-1.5m length,and you take a piece of plastic tubing that just big enough to contain the paintballs,or lead balls :o. The tricky part is to have the ball fit snugly in the tube,having to PUSH it in. The plastic tube should be about 1.5" length,one end melted,and flattened.Drill a hole trough the two joined walls of the pipe,tie it unto the end of the whip. The tube could also be cut in longitudinally,in a cross,if the ball is stuck too hard.The plastic can be heated and formed to the right shape and size,to be just right. The ends of the cut in pipe could be heat bent like small hooks to contain the ball.
You take the whip,make a "whip  crack" that would crack in front of you and the ball should be flying out damn fast.
I know this would work because i've heard that shepherds used to tie small stones with the cracker,and whip it quite a distance and with decent accuracy.And a guy who told me about this,showed me,and he wasn't good at it,but he threw a pebble like 40yards,quite flat,and very fast,almost like a sling. With the tieing method is insecure,especially with round ammo,but the tube should give a consistent release. Accuracy would still need practice,but if you want something that's easy to be accurate with,use a slingshot,or a paintball marker ;)

---

This may be a stupid question... but have you guys tried to replace a part of the string with a rubber band?

I have no idea what would happen... but the results may be interesting.

JoergS wrote on Sep 17^th, 2012 at 8:16am:

... but have you guys tried to replace a part of the string with a rubber band?

[Makes the sign of the cross and steps back three feet] With WHAT?

Jlasud,

I would use a lighter sliding weight ( a half of yours) and put the "release mechanism" just near the pouch. Anyway, good job!

JoergS wrote on Sep 17^th, 2012 at 8:16am:

This may be a stupid question... but have you guys tried to replace a part of the string with a rubber band? I have no idea what would happen... but the results may be interesting.

In general this takes energy away from the release since the rubber band doesn't "snap" back until after the projectile has left the sling.

Dan said in another thread (when I asked what a compound sling is):


Quote:

It's basicallly a sling that opens up even more upon release so you get the feel of a shorter sling but the velocity amplification of a long sling

That is exactly what rubber instead of string would do. You start out with a shorter band, and have a longer band at release.

Elongation isn't exactly the correct idea behind the theory of a compound sling. Unfolding or unfurling in a taut elliptical or curvilinear path is generally the more accepted school of thought.. I still think we should teach a dwarf how to sling and then swing the dwarf from the end of a rope. Properly timed, it would prove incredibly powerful...and entertaining.

More realistically I believe in a compound staff sling. Jeorg could use rubber in it as well. If the staff were two piece and hinged, and rubber was used to pull the pieces from a folded position to a straight one. Much like the spring assisted handheld clay pigeon throwers.


Here, I've drawn a concept picture of what I'm trying to explain.  The orange projectile in the pouch would be loosely held in some sort of clip or detent  that would just barely hold onto it and basically keep the loaded pouch in place while the sling cords are slack.

The position of everything in the drawing is neither "at the ready" nor full release, but at a moment just after release where the cord slack is gone.  The next thing that would happen as the rubber(drawn in red) pulls the jib lever into a full extension, is the release of the pouched projectile from it's lightly held arming clip.

I haven't drawn a release or trigger that would hold the jib arm to the handle when "cocked", you might not need one and may be able to get away with holding it closed with a spare finger (if done right I'd imagine there would be quite a bit of let-off when folded.

---

I will get my new professional grade slomo cam tomorrow, much better resolution! My biggest investment so far. Costs as much as a nice brand new car.

I will record a swing with and without rubber, just to find out.

JoergS wrote on Sep 17^th, 2012 at 10:14am:

Dan said in another thread (when I asked what a compound sling is): Quote: It's basicallly a sling that opens up even more upon release so you get the feel of a shorter sling but the velocity amplification of a long sling That is exactly what rubber instead of string would do. You start out with a shorter band, and have a longer band at release.

He was wrong, that would not work.

The compound sling was designed to sling lighter weight projectiles with a higher speed than is normally possible with a sling. Potential Energy is stored in the ballast and transferred to the projectile as Kinetic Energy during the second, automatic release. The compound sling works just like a staff sling at the moment of release, but the complicated booster mass mechanism makes it so that the second sling moves faster than a staff sling ever could. Basically, the compound sling is a sling on the end of another sling.

C_A did a great job of explaining the benefits, and operating principles of the compound sling.

Curious Aardvark wrote on Mar 25^th, 2007 at 8:30am:

Not so adaxl the enrgy you put into the booster mass is converted directly into the missile via the longer cord. What it should allow you to do (if correctly made and working) is to put a lot more strength into the throw itself. The heavier the missie in a normal sling the harder you can pull against it without straining your own muscles (it's like throwing a punch and missing, the hader you punch the more you hurt yourself when you miss). The problem with a conventional sling is that sure you can use heavier ammo and up to a point you will get more distance. But at a certain weight your own strength will start to tell against you and the velocity will drop - even if you are putting more effort into the throw. With this method you can put a lot of effort into a fairly slow throw which is then directly converted into a much faster throw with a lighter missile. If it helps, think of it as gearing. High gearing on a bike lets you push really hard and pedal slowly but the wheels go round faster than low gearing where you pedal faster but with less effort and the wheels go round proportionally slower.

Curious Aardvark wrote on Mar 27^th, 2007 at 6:02am:

Ah ha finally a bit I can answer again lol Forget the maths and the mechanics - don't have the inclination to tackle those, but I do actually understand the principle involved and for me jureks drawing makes things perfectly clear. And I do know about the physiology :-) Funslinger The main reason we get sore joints when attempting to sling missiles - literally - out of sight,  is that we are moving our joints as fast as we can to transfer that speed into the sling. And to a certain extent even with a reasonable weight missile we're still putting in a lot more effort than can be efficiently translated into the missile (we're back to the punching and missing again). This method relies on the slower application of force. It's like picking something fairly light up from the ground and doing so as fast as you can. Very easy to bugger your back up. If you pick something much heavier up with a more measured lift, your body will be working more efficiently and less likely to cause problems. This compound sling works on the same principle. You are expending the same amount of energy, but in a more controlled and efficient manner. Also you are using a much longer release cord - so effectively, if it works, you can sling with a 6 foot sling while retainng the velocity that you can manually impart to a 3 foot sling. The impact on the slingers body should be less because your muscles are working more in harmony and with greater efficiency.   :-) I do have to say matthias that yureks design [sliding booster mass] does look a lot more elegant than yours sounds ;-)

JoergS wrote on Sep 17^th, 2012 at 12:43pm:

I will get my new professional grade slomo cam tomorrow, much better resolution! My biggest investment so far. Costs as much as a nice brand new car. I will record a swing with and without rubber, just to find out.

I suggest you don't. The rubber will introduce unpredictability to your shot and throw off your accuracy. You may hurt yourself.

Masi is right. I miswrote (oversmiplified) and was (understandbly) misinteprated. That's why I added the link to the dozen page thread (this one) because I figured my one sentace reply wouldn't quite explain the compund sling clearly.

I'm fairly certain we have already had guys try to sling with rubber cords and the reasults were pretty disapointing. Generally just less power, and highly inconsistant release timing.

lol and all because I bought 1000 paintballs 6 years ago and discovered they were too light to sling.

I have over the last couple of days. Found my barnett black widow. found a new band (old one had rotted) managed to fit in incorrectly and puncture one side of the band. Cut band shorter, lost one of the connector widgets, ended up using one freely rotating widget and one non-rotating one.

And so far managed to miss my target post completely about 20 times.
The paintballs definite fly fast, but they also fly unbelievably high.
we're talking from 10 feet I'm aiming at the bottom of a six foot pole and it's still going over the top  :o

It's just occured to me that maybe it's because I've been holding the slingshot sideways. Okay, I'll try tomorrow with a vertical hold. And then look at dismembering my silicone exercise band and making a joerg style slingshot.
Hopefully poundland still sell them as I do use it for exercises  ;D

And joerg - compound sling with rubber bands - I'd love to see that (although initially from a distance) :-)
Not sure how or where you could apply the rubber, but all rubber is doing is storing energy. So maybe the energy from the heavy weight could be temporarily stored in by stretching the rubber - though how you'd thgen pass it on to the rest of the sling, not a clue

But I do think the main problem with the slings people are making is that the initial energy storage weights are not Heavy enough. I'd think nearer the 1kg/2lb mark would fit the concept better than a light weight.

All though it does depend on the weight you intend to sling. For paintballs a much lighter weight wuld probably be best.

I like the whip idea jlasud - but I think the sensible way is probably going to be a slingshot.

Yurek wrote on Sep 17^th, 2012 at 9:48am:

Jlasud, I would use a lighter sliding weight ( a half of yours) and put the "release mechanism" just near the pouch. Anyway, good job!

This is what i would have done next,but didn't had much time on my hands. It's good to read from someone who made a successful compound sling that my intuition was right about what would have to be done. ;)
A pic or some details about yours would be great Yurek!

Jlasud,

I have no picture of my compound sling. It was a temporary design just to test the principle. The sliding mass (ca. 110 g) I made of my 90g lead glande and a special screw with smooth eye. The pouch was long enough to keep reliably a 20g soft stress ball which I used as secure ammo. The free/release end of the pouch had a small loop that was connected by a short dulled nail :D with a little bit longer loop tied on the retention cord close to the second end of the pouch. The release "mechanism" was similar to the one used in my "nail arrow sling" - look at the picture and imagine the small loop as a shaft of an arrow.

The adjustable "pull-ail-off" string (1mm dyneema) was tied to the retention/sliding cord just before the sliding mass, just like at your picture. I used the same sliding knot I use in my adjustable slings.

I slung with that sling a few small stones only. But the releases weren't as clear I would like because of too big pouch and probably some jerk of the release mechanism. Anyway, at my guess, the light stones were launched at least as fast as I could sling them with normal sling. The stress ball clearly faster - what some of you have seen on a video. Accuracy was an another problem.

As I wrote once, the compound sling to work perfectly require more advanced engineering and tuning. As result we would get a device as complicated as a compound bow :D

It's funny how with all the tests of different modern slings and ammunition,the traditional sling and ammo is still the top ranking :D KISS keep it simple,slinger

So,i played a bit with the calculator and some facts.
World champ hammer throwers throw their 16 pound hammers with ~ 60mph /96km/h /26.6m/s which yields 2568 J !!!

An AK 47 bullet does 2100 J !!!

An average sling throw ~ 160 J (like an average .22 LR)

9x19mm PB ~ 490 J

So, if one could transfer 2000J in a compound sling into a 100g projectile,it would propell it 100m/s
If someone would type that in their ballistic simulator,we could get a range for it.

jlasud wrote on Apr 1^st, 2013 at 10:47am:

So,i played a bit with the calculator and some facts. World champ hammer throwers throw their 16 pound hammers with ~ 60mph /96km/h /26.6m/s which yields 2568 J !!! An AK 47 bullet does 2100 J !!! An average sling throw ~ 160 J (like an average .22 LR) 9x19mm PB ~ 490 J So, if one could transfer 2000J in a compound sling into a 100g projectile,it would propell it 100m/s If someone would type that in their ballistic simulator,we could get a range for it.

Could you plug in for one of my 8 oz slingstones(I get pretty dang good velocity with those)?
I really want to know!

SS,
These data was calculated using the KE=1/2 x mass x velocity square
You gotta measure your stones speed,than calculate.
Simplest is to measure out a distance,sling,record with camera, look in a video edit program,how many 1/100 of a second it took to get there,and you get your speed.

This is some algebraic stuff.

jlasud wrote on Apr 1^st, 2013 at 5:25pm:

SS, These data was calculated using the KE=1/2 x mass x velocity square You gotta measure your stones speed,than calculate. Simplest is to measure out a distance,sling,record with camera, look in a video edit program,how many 1/100 of a second it took to get there,and you get your speed.

There is a simpler way if one isn't too bothered about accuracy. This is for estimating the kinetic energy based on how far you can throw something, so it obviously applies to distance shots rather than anything 'close to'.

You measure two things:
1. The weight of your projectile.
2. The distance you can throw it to first bounce on flat ground.

You express the weight in kilograms, and the distance in meters. (Sorry about that :))

Multiply the weight by the distance, multiply by 10, and divide by 2. That gives you a quite good estimate of the initial kinetic energy in J.

eg. Slinger X throws a 250g (0.25kg ie. a bit over 8oz) a distance of 100m.

 (0.25) x (100) x (10) = 250.

 Divide by 2 gets you an energy of 125J.

This all assumes air resistance doesn't matter, which is likely true for this example. The reason the formula works? That's algebra, this is just arithmetic ;D

There no guarantee that you can impart 2000J into the projectile especially because the more mechanically complex a system is, the more energy will be lost due to entropy. To put it another way, we can only push as hard as the system will let us and we can only do that as efficiently as the system will let us. We're also doubly disadvantaged, our projectile is low mass and low intertia when compared to a hammer and high surface area compared to a bullet. It will slow down and bleed energy faster than either of the objects used for comparison. Terminal ballistics (what we can see) are more dependent on momentum than kinetic energy, and the formula for that is p=m*V. It's a little simpler than the formula for KE. Momentum is conserved, so we can reasonably say that our projectile will start with the same momentum as the booster mass will have at the end of its travel.

Hm... I will try both methods. Which is more accurate?

squirrelslinger wrote on Apr 2^nd, 2013 at 3:24pm:

Hm... I will try both methods. Which is more accurate?

Between jlasud and wanderer? Jlasud.

You can also set up a big target at a fixed distance with a camera in between you and the target. Measure the time between seeing/hearing the release and hearing the impact on the target using a stopwatch. That's going to be more accurate than looking at frames in a video editor unless you're using a high speed camera.

squirrelslinger wrote on Apr 2^nd, 2013 at 3:24pm:

Hm... I will try both methods. Which is more accurate?

I would agree with Masi - in principle anyway. Jlasud's formula is the definition of kinetic energy, so should be the way to go,...

But first, you are probably only after an approximate value anyway, and measuring distance is a lot easier to do than measure the speed. With the 'round numbers' I gave, the distance measurement compensates roughly for things like air resistance and so on.

Second, you need a pretty accurate value for the velocity if you are to plug it in to the formula for kinetic energy. As has come up before, the best way to measure the velocity is from the sounds of release and impact. Rather more trouble I think, but try both and let us know what values you get. :)

jlasud wrote on Apr 1^st, 2013 at 10:47am:

So,i played a bit with the calculator and some facts. World champ hammer throwers throw their 16 pound hammers with ~ 60mph /96km/h /26.6m/s which yields 2568 J !!! An AK 47 bullet does 2100 J !!! An average sling throw ~ 160 J (like an average .22 LR) 9x19mm PB ~ 490 J So, if one could transfer 2000J in a compound sling into a 100g projectile,it would propell it 100m/s If someone would type that in their ballistic simulator,we could get a range for it.

I eventually have got the Working Model 2D" working (demo version is available) which Matthias "discovered" and used for research of compound sling ideas some years ago. Unfortunately the program didn't want to work on my computer in that time.

The link below is to a short video showing an example simulation of a "compound sling machine". It corroborate the "sliding mass" idea nicely and some interesting conclusions can be drawn from it.

Some data:

projectile/booster mass ratio     1/3
arm length                             0.9 m
arm initial velocity                   12 rad/s
arm acceleration                      40 rad/s^2  (permanent)
booster initial velocity               1.84 m/s
no gravity (more suitable to movements in the horizontal plane)
no mechanical friction
some air drag


https://www.youtube.com/watch?v=jXjyyMqGv5A

My video capture software didn't do its work as I would like.


Jlasud,

Now I am going to simulate how a hammer thrower could transfer energy to an ak47 bullet :)

Ooh, cool! Was that, by chance, as complicated as you could make the system using that program or could you have included variable arm acceleration and internal forces (friction, normal force, etc) for the member interactions? It would be useful to know how far I can take the software when I'm dummying up a compound sling.

Well,i didn't said it's possible,just let my fantasy run amok.
And i mentioned 2000 J out of 2500J of a world champ throw.
Yurek,looking forward to that simulation also, although an ak47 bullet weights ~ 8g so it's waay too light.

Masiakasaurus,

Yes it is possible to make the simulation more complicated. You can change the arm acceleration with any function you want. Torque and velocity either. Additionally there is possible to use own scripts. You can also measure all interesting values - get series of numbers and charts. Unfortunately there is no possibility to simulate friction of the pulley. One of the charts in the movie shows tension of the pulley system, what gives an idea about normal forces.

I omitted the slinger's whole body mechanics - too complicated and not enough data. The arm just accelerates constantly regardless of external load. You may want to apply torque instead, then the whole complicated interaction of slinger's body with the sling becomes very important.

Anyway the simulation is much closer to reality than our guess :)

Jilasud,

anyway I will try ;)

That sounds fairly useful. I'm generally better working directly with applied moments (torque) than with tangential forces that induce moments.

Masiakasaurus wrote on Apr 5^th, 2013 at 4:03pm:

That sounds fairly useful. I'm generally better working directly with applied moments (torque) than with tangential forces that induce moments.

It seems to be more suitable in this case indeed. But no problems with torques in WM 2d.

i honestly dont have the time or energy to look thourgh 15 pages of compound sling discussion. Have we found out a viable way to use it, or even confirmed that it works at all?

hassan wrote on May 28^th, 2013 at 6:39pm:

i honestly dont have the time or energy to look thourgh 15 pages of compound sling discussion. Have we found out a viable way to use it, or even confirmed that it works at all?

As far as I know, there is not a viable way to use it, except for a few prototypes.

It does work... I think.

A quick google search will give you pictures of one compound sling prototype in use. Now it's just being refined. Here's the relevent post. http://slinging.org/forum/YaBB.pl?num=1174772635/60#61