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The Slingshot Channel Thread

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Unread postAuthor: jackssmirkingrevenge » Wed Oct 10, 2012 8:26 am

POLAND_SPUD wrote:shame to admitt but I've never disasembled a dildo - I assume there is an excentric mass mounted on the shaft of an electric motor, JSR is that right ?


HAHAHAHAHAHA!!!!

:oops:

Yes...

Image

No wait, that was the very first prototype :P

Image

That's more like it.

anyway what if the mass was perfectly balanced and acted as a gyro? how fast would it have to spin or how heavy it would have to be to stabilise an inherently instable projectile??


Interesting idea.

I've often thought that a way to avoid rifling was to have the barrel mounted on bearings and spun by a motor, but never actually putting the motor in the projectile!
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Unread postAuthor: POLAND_SPUD » Wed Oct 10, 2012 9:44 am

I've often thought that a way to avoid rifling was to have the barrel mounted on bearings and spun by a motor, but never actually putting the motor in the projectile!
yeah it might make sense assuming that it doesn't require insane mass or RPMs... not as much useful for small projectiles as it could be for larger ones - like 1" in diam and bigger
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Unread postAuthor: al-xg » Wed Oct 10, 2012 1:03 pm

Well any of the calculations I've done for rifling, even for airguns, have involved much higher RPMs than electric motors generally achieve.
IIRC along the lines of 90k-150k RPM possible quite a bit more.
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 10, 2012 4:23 pm

al-xg wrote:Well any of the calculations I've done for rifling, even for airguns, have involved much higher RPMs than electric motors generally achieve.


A typical 45 ACP twist rate is 1 turn in 16 inches. Travelling at 850 fps, typical speed from a pistol, this means 637 revs per second, which equates to 38,250 rpm. This is well within what a good electric motor can achieve, especially if you have a say 5:1 pulley drive. Also, you don't have to spin the whole barrel either, just the breech will do.

Of course for a longer spitzer type bullet you would need a much higher spin rate, but still, certainly shortish projectiles at high subsonic velocities can realistically be spun using easily available off-the-shelf motors.

Surely something like this would fit the bill for something like a 0.5" slug:

http://www.ebay.com/itm/Brushless-Motor ... 20c6a8fdbc
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Unread postAuthor: POLAND_SPUD » Thu Oct 11, 2012 12:00 am

A typical 45 ACP twist rate is 1 turn in 16 inches. Travelling at 850 fps, typical speed from a pistol, this means 637 revs per second, which equates to 38,250 rpm.
and that's at the muzzle - so I'd assume that less is required to keep it stable
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 11, 2012 12:36 am

The spin rate is preserved pretty well in flight: http://www.nennstiel-ruprecht.de/bullfly/faq.htm#Q8

Remember there isn't much drag on the rotational forces.

http://kwk.us/twist.html

Say you have a lead slug, 12.7mm diameter, 20mm long.

At 500 fps we get one turn in 25 inches, equal to just 14,400 rpm.

Increase that to 1000 fps and you need 20,000 rpm, very achievable in my book.
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9" nails as ammo: New slingshot pumpgun!

Unread postAuthor: JoergS » Sun Dec 23, 2012 11:59 pm

Here is my latest work... a repeating slingshot crossbow, shooting 9 inch nails.

This is in continuance with my Chu-Ko-Nu based design line. This time, it is bigger than the pencil shooter, but a lot smaller than the chest mounted spear launcher.

The ammo is - nine inch (23 cm) nails. Those are cheap, about 8 Euro-cents a pop (10 Euros for 120 of them). Of course you have to cut of the head, done in about one minute.

The repeating action is done by pressing the butt against the chest and pulling back with both arms, like in a rowing machine. This is needed as you need a lot of draw force to throw the heavy nails - each weighs 76 gramms (1276 gr). The magazine fits ten of them.

With a bit of extra effort, you can very easily enhance the tip by sharpening it. I even hardened the tip of this one.

It works great. I may add more rubber soon, but already this is very effective. Like a Chu-Ko-Nu, but more compact and with a trigger!

[youtube]http://www.youtube.com/watch?v=95Xm-YT4FZ0[/youtube]
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9" nails as ammo: New slingshot pumpgun!

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Unread postAuthor: Fnord » Tue Jan 01, 2013 6:54 pm

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Unread postAuthor: Technician1002 » Tue Jan 01, 2013 8:11 pm

Saw that, but discussion of the projectile is against forum rules. Nuf said.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 02, 2013 4:12 am

Ah excellent, ever since playing Imageuake as a teenager I've wanted to use nine inch nails as ammunition...

Image

Joerge, ever thought of upping the ante and motorising one of your repeaters for a full auto bolt thrower?

Something like this but with more cojones:

[youtube]http://www.youtube.com/watch?v=QS4RKoRyTik[/youtube]
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Unread postAuthor: JoergS » Wed Jan 02, 2013 4:21 am

I thought about that. Problem is that then I foresee legal issues here. A crossbow is largely unregulated, an exception in our pretty tight laws regarding home made weapons. But the definition of a crossbow includes that it is powered by muscle energy.

I abide the law, even if I don't really understand it.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 02, 2013 6:03 am

I see... well in that case, if they can make a pedal powered washing machine, just saying ;)

http://www.maximizingprogress.org/2009/ ... shing.html

It wouldn't be portable, but maybe some sort of siege engine ballista type device that's pedal powered...
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Unread postAuthor: JoergS » Wed Jan 09, 2013 6:59 am

OK, we all know that front heavy bolts need no fletching for a straight flight.

What if...

Image

Image

This January. On The Slingshot Channel. Stay tuned.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 09, 2013 7:06 am

:shock:

Is this about to become a reality?

http://www.militaryphotos.net/forums/sh ... -action%29
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Unread postAuthor: JoergS » Wed Jan 09, 2013 7:09 am

Kind of. But I will be using this launcher:

Image
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