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Message started by WildAtHeart on Apr 8th, 2004 at 10:46pm

Title: New user, New idea
Post by WildAtHeart on Apr 8th, 2004 at 10:46pm
Hey guys,

I am pumped about finding this forum! I've been into slinging, slingshots, and throwing knives for a long time, since middle school at least. It was 9th grade when I contructed a sling out of some thick leather and parachute cord, and I still have it today! In fact I was out on the trail today testing my mettle against some trees.

Now that you know my story, I wanted to run an idea past you guys.
I love how the sling has a history in many cultures and even the Bible, but, being a fellow with an inqusitive mind, I wonder if our modern materials could make a more powerful or accurate sling, hopefully keeping it as simple and elegant as possible.

I was thinking, what if I took a leather pouch, attached two 6 or 8 inch pieces of 1/2 inch latex tubing, then on the ends of those sections attach cord like a regular sling? The elasticity of the tubing (basically slingshot tube) might very well add velocity if the sling is wielded correctly.

When I get home from vacation I plan on constructing one of these. I'll let you all know how it turns out!

Title: Re: New user, New idea
Post by TechStuf on Apr 8th, 2004 at 10:50pm
Hopefully I can save you some wasted effort.  I tried this when I was 14 by cannabalizing a sling shot of mine and quickly learned a valuable physics lesson.  The effect produced will actually dramatically lessen efficiency.  Your traversing arc is widened and energy is stored in the bands with no way to be recouped.  Ever lean out quickly on a merry-go-round?  Same effect.  Keep brainstorming though....you may hit the jackpot! ;)

Title: Re: New user, New idea
Post by TechStuf on Apr 8th, 2004 at 11:05pm
I am digging around here in storage trying to find my compound sling.  It uses simple, solid physics principles to really spit out the ammo!  It is not as accurate (in present form) as the basic sling but is fassssst!  To give you an idea,  it uses a simple leverage principle to shorten the radius on the traversing arc at the moment of release to produce higher velocities.   Pros and cons:  PRO-very fast.  PRO-No arm jarring yank at release like some of my earlier designs.  PRO-works great and easy to make!   CON-uses one 2.5oz projectile to increase the velocity of a 1.25oz projectile.(Of course these numbers can be scaled to the user's satisfaction)  CON-totally alien sling dynamics including the necessity of releasing sooner than one's honed instincts keep telling one.  CON- One is sacrificing the heavier projectile whose trajectory is always flatter/lower than the main projectile for vastly increased speed. (With an underhand sling style).   One more PRO-It is very fun and challenging!  :) ;)

Title: Re: New user, New idea
Post by Johnny on Apr 8th, 2004 at 11:08pm
Tech is right
If your sling stretches, you will lose stored energy. I also make bows, arrows and strings. When you make your strings, don't let them stretch, it robs energy.
Also, I use natural fibers(sisal) to braid my slings. Nylon seems to stretch a dash for my taste!
Glad you're with us!
Wild at Heart-I read the book also!

Title: Re: New user, New idea
Post by TechStuf on Apr 8th, 2004 at 11:19pm
Johnny,  have you tried the spectra/fastflight serving material or spiderwire/spectra fishing line?  It is excllent material for our application.  ;)

Title: Re: New user, New idea
Post by Johnny on Apr 8th, 2004 at 11:26pm
I use Dacron
I think it is similar to Fastflight. Maybe not.
Are you saying this is good for slings also, or just bowstrings?
Thanks Tech!
Johnny

Title: Compound sling?
Post by Matthias on Apr 8th, 2004 at 11:31pm
I was lying awake last night trying to work out an approach to this. I think I need a few more hints to figure out what you were doing though...

My sling looks like it is tending toward using a captive "booster" weight, and the pro/con list seems similar - speed, smooth, simple / release point difference + sensitivity to timing, possibility of getting beaned in the noggin with a captive "booster" in a somewhat unpredicable (but thankfully energy depleted orbit)

I'm headed home for easter, so hopefully I'll get a chance to throw some trials in a non-urban environment. Highly recommended for experimental sling work!  ;D

Matthias

Title: Re: New user, New idea
Post by TechStuf on Apr 8th, 2004 at 11:33pm
Both actually.   Spectra fiber has a much lower coefficient of stretch than traditional materials.  This gives both the archer and the slinger very similar gains in velocity.   On the order of 10-15fps or so.   This may not seem worthy of attention but can make the difference between a hit and a miss on the long shots for both sports.

Title: Re: New user, New idea
Post by TechStuf on Apr 8th, 2004 at 11:36pm
Matthias,  I will try and get a pic posted soon.  Sooner if I find my original and don't have to make another one.  They are fairly easy to make though, so in either case,  I should be posting soon.

Title: Re: New user, New idea
Post by Johnny on Apr 8th, 2004 at 11:38pm
I'll braid a sling using Dacron!
I seem to remember that someone on this forum used Dacron for their sling.
I will give it a try!

Title: Re: New user, New idea
Post by TechStuf on Apr 8th, 2004 at 11:50pm
Actually Johnny, the traditional string material to which I was referring is the Dacron material.  The Fastflight/Dyneema material is made of spectra fiber which stretches so little that it is not recommended for most bows with wood risers.   It is vastly superior to B50 Dacron in the stretch department and also is much more abrasion resistant.

Title: Re: New user, New idea
Post by WildAtHeart on Apr 9th, 2004 at 11:29am
So non-elastic strings are the best? I wish I knew some physics equations to help me figure this out. I have the worst physics teacher ever  :P

One question - what is a compound sling?

Title: Re: New user, New idea
Post by mgreenfield on Apr 9th, 2004 at 12:11pm
Yeah, I'm wondering, too!   What's a "compound sling"?   mgreenfield

Title: Re: New user, New idea
Post by Yurek on Apr 9th, 2004 at 12:44pm
Welcome WildAtHeart!

Interesting topic. I also thought about the sling with a "booster" at one time. I had an idea of the sling which loses the additional mass during the final whip. The idea of shortening of sling during the throw is very interesting. I'm also curious.

Jurek

Title: Re: New user, New idea
Post by english on Apr 9th, 2004 at 1:25pm
I make my strings for my bows with hemp.  I make slings with either hemp, cotton (because it is cheap), wool, and once, nylon.  Crossbow strings I make with braided cotton, because it makes a string the perfect size to fit Chinese crossbow mechanisms (my favourite because they are very simple and effective).  I really, really want some yak hair for slings, because it is tough and easy to dye.  It is very expensive though, about five pounds for a roll big enough for about half a sling.  So being permanently short of funds, I haven't got any.  Maybe for a birthday or something.

Title: Re: New user, New idea
Post by TechStuf on Apr 9th, 2004 at 1:47pm
It is rather like a robust, lightly constructed Trebuchet at the end of a sling.   I will draw a sketch for you to consider until I get time to get one on the board.   It is a fun curiosity that never really found favor with me as the Pro/Con list balanced out with no real advantage to be gained in the end.   But a nice curio it is.....

Title: Re: New user, New idea
Post by WildAtHeart on Apr 9th, 2004 at 1:51pm
like a stick with a sling on the end? I made one of those once with a hockey stick. It was really clumsy, but it allowed me to throw big stones FAR.

Title: Re: New user, New idea
Post by WildAtHeart on Apr 9th, 2004 at 2:12pm
here's my idea on the physics of a sling with an elastic portion:

In an overhand throw, the stone is swinging from in front of you to behind you, with the strings taut the whole time. Then, when the stone is at about 6 o'clock or before, you twist your torso and throw your arm and shoulder forward, thusly pulling the stone with you and accelerating it. When the stone is at 3 or maybe 2 o'clock is when the greatest tension is on it. If there was a piece of elastic in the cord, then at that point the band would stretch due to the tension. From there I'm not sure what the result would be. It seems like it might propel the rock faster - imagine pulling a loaded trailer with a truck. If its connected with a chain, that's like a conventional sling. However, if the connection was a stretchy cable, the trailer would *snap* forward when the tension in the elastic cable becomes too great. I think the same effect would happen with the sling.
What do you think?

Title: Re: New user, New idea
Post by TechStuf on Apr 9th, 2004 at 2:40pm
Ok,  here is an oversimplified sketch.   My original was of somewhat different construction and materials.  This sketch in no way conveys the deceptively complex dynamics of such a system.  One must work out the desired angle of departure of the leverage weight as well as the ammo.  It requires tweaking to find the sweet spots!   (This would of course be eliminated in a solid production model).   After several throws with a 'captive leverage weight' model and the resultant recoil....I found that releasing the leverage weight at the correct moment provided satisfaction.
(Oh the depths of fanatical obsession one can reach in any endeavor!) .......suffice it to say,  I have much stranger devices than this.   Yes indeedy......


http://www.ezimagecenter.us/image.cfm?ImageID=3608

Title: Re: New user, New idea
Post by TechStuf on Apr 9th, 2004 at 4:07pm
I almost forgot.....welcome to the forum WildAtHeart.   To quote you:

"I wish I knew some physics equations to help me figure this out. I have the worst physics teacher ever".


I wish you did too, WildAtHeart.    I wish you did too..... :-/  ;)   I have always been a bit 'reversed' when it comes to equations.....

Title: Re: New user, New idea
Post by WildAtHeart on Apr 9th, 2004 at 5:04pm
I'll try my best though. I bet I can dig out some equations about centripedal force and stuff. I slept through that class though  8)

Title: Re: New user, New idea
Post by Hobb on Apr 9th, 2004 at 5:06pm
Techstuff:  All I can say is "Wow."  That's quite the device.  Do both missiles go forward?  

Wildatheart:  Welcome!  I think, with elastic cords, they wouldn't so much snap forward as they would continue to extend and then snap back into shape after the release.  If you accelerate your swing at a constant rate, centripetal (O.K., centrifugal, although my high-school physics teacher says there's no such thing) force will continue to increase until you release -- more force, more speed, and more extension of the cords until you let go.  Also, since the cords start off as shorter, you're robbing yourself of leverage through the initial portion of the swing.  If you could make a sling go from longer to shorter, you'd get more speed/power/distance, but with elastic cords I think you'll be going from shorter to longer, giving yourself less speed/power/distance.  I don't have any equations for you, and my last physics course was some time ago, but that's what makes sense to me.

Title: Re: New user, New idea
Post by TechStuf on Apr 9th, 2004 at 5:09pm
Hobb,  yes they do, albeit at different angles and velocities.  The trick is designing the device to release both at the moments desired.

Title: Re: New user, New idea
Post by Matthias on Apr 9th, 2004 at 7:16pm
Wow indeed! That's quite the sling! I hope you can dig up an example and share it... maybe even a video?  ;)

This is at right angles to what I was thinking about, so I'll carry on this weekend (I'm out of the city with room to throw!) and let you guys know how it pans out.


Title: Re: New user, New idea
Post by Chris on Apr 10th, 2004 at 1:27am
Welcome WildAtHeart,

The problem with elastic cords is that the harder you sling, the more they stretch.  When they stretch, it doesn't go any faster.  And, as other people mentioned, all that energy you exert making it go faster is really just stretching the elastic, which is not what you want.  With "rigid" cords, all your energy goes into the speed of the projectile.  

Chris

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