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The Slingshot Channel Thread

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Unread postAuthor: JoergS » Sun Oct 18, 2009 9:34 am

Here is the vid:

[youtube]http://www.youtube.com/watch?v=1L4U9yNGP4A[/youtube]

Video embedded by jrrdw.
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The fastest slingshot ever! 15 Shot magazine.

Unread postAuthor: JoergS » Sun Oct 18, 2009 11:07 am

I think with this slingshot, I am hard to beat!

Question is if my innovation is still a slingshot... but it is rubber based, and has no trigger mechanism.

[youtube]http://www.youtube.com/watch?v=hB8z1iH2tQ0[/youtube]
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Unread postAuthor: jackssmirkingrevenge » Sun Oct 18, 2009 11:35 am

Next up, I expect to see this fitted to some sort of mechanical reloading contraption for the world's first full auto slingshot :D
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Unread postAuthor: JoergS » Sun Oct 18, 2009 11:51 am

Thought about that already. A Gatling (crank operated) mechanism would be legal here.
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Unread postAuthor: boyntonstu » Sun Oct 18, 2009 1:36 pm

Have you measured the speed gained from Momentum transfer?
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Unread postAuthor: D_Hall » Sun Oct 18, 2009 1:51 pm

Just a thought but....

Have you considered putting the magazine at the back of the rails? The idea being that instead of an impact to drive the ball (which is going to be an inefficient driver) you just pick up the ball on your way forward and release normally.
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Unread postAuthor: Ragnarok » Sun Oct 18, 2009 2:04 pm

On a similar note to D_Hall, I have an idea... put a magnet on the "carriage" - pick up the ball at the front, draw back and shoot. (You would need to sort out a way to stop another ball moving into position in the mean time, but that's possible.)

If you stop the carriage sharply enough, then the magnet's attraction on the ball would be easily broken, and its inertia will keep it moving.
Bear in mind, you're already losing a bit of energy accelerating the ball off the magnet as it is - this wouldn't be any worse.
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Unread postAuthor: potatoflinger » Sun Oct 18, 2009 2:23 pm

Ragnarok wrote:You would need to sort out a way to stop another ball moving into position in the mean time, but that's possible.


That could easily be accomplished with a spring loaded system similar to the type of ammo dispenser that comes with many slingshots, just mounted on the handle of the slingshot and controlled by the left hand of a right-handed shooter.
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Unread postAuthor: JoergS » Sun Oct 18, 2009 2:36 pm

Well, the whole idea is to increase the speed of the bullet so that it is faster than the retraction speed of rubber.

(Tubular) rubber won't retract faster than about 60 meters per second (flat bands can be a little faster, but not that much).

So even with very small bullets, 60 m/s is max for a slingshot.

Stu and I have been testing all kinds of methods about increasing that speed. I have to admit that Stu is much more sophisticated as he is a trained physicist, but I do what I can.

I tried air (remember the airowgun vid?), and it works, but is not very practicable. I tried a transmission, too much friction. Stu tried air, too, and also is experimenting with levers.

Now the elastic collision is another theoretical chance.

If you want to shoot a football with your car bumper, what would be more effective - accelerating it and hit the brake so it keeps moving, or accelerate without it and hit it when you are doing 100 mp/h?

The rules of the elastic collision say: If a heavier object hits a lighter, unmoving object, then the lighter object will be kicked off FASTER than the heavier object, which will loose speed, but still continue its course.

The larger the weight difference, the more apparent is the effect. But the formula limits the speed difference to 2 (the lighter object goes twice as fast as the original speed of the heavier one, the heavier object is slowed to half of its original speed).

Means: The heavy sled kicks the lighter ball off with MORE speed. Accelerating both objects together would be SLOWER, not FASTER.

With the black bands, the 15 mm balls do 65 m/s! A slight success, but I guess a less heavy sled and smaller bullets would make sense.

Jörg
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Unread postAuthor: boyntonstu » Sun Oct 18, 2009 2:56 pm

JoergS wrote:Well, the whole idea is to increase the speed of the bullet so that it is faster than the retraction speed of rubber.

(Tubular) rubber won't retract faster than about 60 meters per second (flat bands can be a little faster, but not that much).

So even with very small bullets, 60 m/s is max for a slingshot.

Stu and I have been testing all kinds of methods about increasing that speed. I have to admit that Stu is much more sophisticated as he is a trained physicist, but I do what I can.

I tried air (remember the airowgun vid?), and it works, but is not very practicable. I tried a transmission, too much friction. Stu tried air, too, and also is experimenting with levers.

Now the elastic collision is another theoretical chance.

If you want to shoot a football with your car bumper, what would be more effective - accelerating it and hit the brake so it keeps moving, or accelerate without it and hit it when you are doing 100 mp/h?

The rules of the elastic collision say: If a heavier object hits a lighter, unmoving object, then the lighter object will be kicked off FASTER than the heavier object, which will loose speed, but still continue its course.

The larger the weight difference, the more apparent is the effect. But the formula limits the speed difference to 2 (the lighter object goes twice as fast as the original speed of the heavier one, the heavier object is slowed to half of its original speed).

Means: The heavy sled kicks the lighter ball off with MORE speed. Accelerating both objects together would be SLOWER, not FASTER.

With the black bands, the 15 mm balls do 65 m/s! A slight success, but I guess a less heavy sled and smaller bullets would make sense.

Jörg


Jörg,

You are on the way to having the fastest repeating slingshot an the faster than rubber slingshot.

I suggest the following test:

A foot rest slingshot like the one you already have with a sled slamming into a 9mm steel ball.

I would like to see 500 fps from rubber.

I would do a speed test without the magnet to determine its effect.

BTW Is this fast loading slingshot accurate?

BoyntonStu
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Unread postAuthor: JoergS » Sun Oct 18, 2009 3:06 pm

Stu, it is fairly accurate, but it has an enormous bounce effect due to the sled hitting with a lot of unspent energy. A longer barrel could make sense, I guess.

The magnet has little or no effect, I tried it without the magnet before I even attached the magazine. I can also push the bullet out with one finger, pressing very lightly. I bought several magnets to make sure, but the weakest one does the job just fine.

If I read the formula of the elastic collision right, then twice the speed is all I can achieve. So going ahead of 500 fps would be difficult. I would have to use a sled that is so light that I can accelerate it beyond 250 fps, which is possible with flat rubber (Thera Band Gold) and bullets weighing about 20 gramms. So I would have to use very small bullets, like the two gramm 8 mm steel bullets.
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Unread postAuthor: D_Hall » Sun Oct 18, 2009 3:31 pm

Interesting thoughts regarding the elastic collision as a means to get "faster than rubber" velocities. Honestly, in the videos it looks like the balls are barely moving. If it's just an optical illusion, fine. I was just going under the assumption that the velocity of the system was lacking.


That said, have you thought about a pully-based slingshot? IE, some sort of system not dissimilar to a compound bow in which the rubber may move at 60 m/s but the pouch is accelerated beyond?
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Unread postAuthor: JoergS » Sun Oct 18, 2009 3:39 pm

The video contains slomos that are recorded at 1200 fps, 20 times slower than real time. That's why they look so slow.

If you look at the real time video part (when I do the 10 shots in a row), you can not even see the ball because it is too fast for the 50 images per sec the camcorder records.

I have tried transmissions and pulleys, but honestly, all these attempts failed. You have to use strings for these, can't use the rubber in a pulley. Lots of friction. I have given up on that route.
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Unread postAuthor: MRR » Mon Oct 19, 2009 11:48 am

Don't know if it sound stupid but have you ever thought of mounting elastic, hard rubber (bouncing ball) to the sled? Like kicking a football that deforms and than transfers the energy into a drive forward.

Could that work, if the energy is not redirected back into the sled?
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Unread postAuthor: JoergS » Mon Oct 19, 2009 1:33 pm

Had to strengthen the welding a bit, the kick is enormous.

Added a longer barrel and attached the much stronger black bands. Much more accurate now!

Image

Image

Jörg

MRR, rubber at the tip of the sled would work, but the force would smash it to pieces in no time.
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