Slinging.org Forum - Compound Sling

pancaker

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Re: Compound Sling
Reply #30 - Mar 27^th, 2007, 7:59am

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.

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sliding_ring_release.PNG

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shabundi

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Re: Compound Sling
Reply #31 - Mar 27^th, 2007, 9:47am

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

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Dravonk

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Re: Compound Sling
Reply #32 - Mar 27^th, 2007, 10:23am

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...

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dravonk-comp-sling-sketch1.png

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Matthias

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Re: Compound Sling
Reply #33 - Mar 27^th, 2007, 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.

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

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Dravonk

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Re: Compound Sling
Reply #34 - Mar 27^th, 2007, 2:09pm

Quote from Matthias on Mar 27^th, 2007, 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. Wink

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!

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curious_aardvark

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Re: Compound Sling
Reply #35 - Mar 27^th, 2007, 2:51pm

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)

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Do All things with Honour and Generosity: Regret Nothing, Envy None, Apologise Seldom and Bow your head to No One - works for me :-)

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Yurek

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Re: Compound Sling
Reply #36 - Mar 27^th, 2007, 4:41pm

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 Roll Eyes

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

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In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.

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Yurek

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Re: Compound Sling
Reply #37 - Mar 27^th, 2007, 5:05pm

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

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In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.

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Yurek

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Re: Compound Sling
Reply #38 - Mar 27^th, 2007, 5:28pm

Quote from FunSlinger on Mar 27^th, 2007, 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. undecided

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

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In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.

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Yurek Funditor Past Moderator The best thing, is a good sling. Posts: 921 Gender:	Re: Compound Sling Reply #39 - Mar 27^th, 2007, 5:36pm 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
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Yurek

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Re: Compound Sling
Reply #40 - Mar 27^th, 2007, 5:43pm

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!

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In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.

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Yurek

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Re: Compound Sling
Reply #41 - Mar 27^th, 2007, 6:10pm

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.

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In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.

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Matthias

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Re: Compound Sling
Reply #42 - Mar 27^th, 2007, 6:41pm

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 Wink

Matthias

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Matthias

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Re: Compound Sling
Reply #43 - Mar 27^th, 2007, 8:22pm

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.

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.

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 Roll Eyes

we'd all have to find bigger places to sling!

Matthias

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Matthias Past Moderator Posts: 1418 Gender:	Re: Compound Sling Reply #44 - Mar 27^th, 2007, 8:24pm 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...
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