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Twist and Shoot

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Twist and Shoot

Unread postAuthor: jackssmirkingrevenge » Wed Jun 13, 2018 6:47 pm

A little idea that came to mind, not going to build it but thought I should share.

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Two cylinders on a common axis, one has the barrel and one has the chamber. A slightly imbalanced piston is trying to push its way out of the chamber but it pushes against the projectile which pushes against the barrel block. To fire, you twist the rear until the projectile is in line with the barrel, at which point the projectile moves forward as does the piston behind it, allowing the gas to escape and push the projectile down the barrel.

By adding multiple chambers like a revolver it could also be a repeater.
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Re: Twist and Shoot

Unread postAuthor: jimmy101 » Thu Jun 14, 2018 10:49 pm

Wouldn't it have some of the same problems as a ball valve? In particular, slow opening time?
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Re: Twist and Shoot

Unread postAuthor: jrrdw » Fri Jun 15, 2018 4:33 am

jimmy101 wrote:Wouldn't it have some of the same problems as a ball valve? In particular, slow opening time?


Nothing that a high speed stepper motor can't fix... :twisted:
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Re: Twist and Shoot

Unread postAuthor: mrfoo » Fri Jun 15, 2018 5:24 am

No need for closely balanced spool valve, the bigger the imbalance the better. Something like a valve from an internal combustion motor would be fine. The problem I see is the projectile dropping slightly into the barrel and opening the valve before it can fire, but that's not insurmountable with a spool type valve - make it slide, for example, 3/4 the barrel diameter before it opens. Indeed, as the projectile will already have some forwards momentum, it could be a pretty good option.
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Re: Twist and Shoot

Unread postAuthor: jackssmirkingrevenge » Fri Jun 15, 2018 2:50 pm

jimmy101 wrote:Wouldn't it have some of the same problems as a ball valve? In particular, slow opening time?


If properly configured the spool would not move forward far enough to open the chamber until the projectile was in line with the barrel, at which point it would open with the speed of a mechanically locked exhaust valve.

No need for closely balanced spool valve, the bigger the imbalance the better. Something like a valve from an internal combustion motor would be fine. The problem I see is the projectile dropping slightly into the barrel and opening the valve before it can fire, but that's not insurmountable with a spool type valve - make it slide, for example, 3/4 the barrel diameter before it opens. Indeed, as the projectile will already have some forwards momentum, it could be a pretty good option.


Keep in mind that the projectile pushing on the barrel portion causes friction, this is why the balanced spool is important, otherwise it would be impossible to turn by hand.
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Re: Twist and Shoot

Unread postAuthor: mako » Mon Jun 18, 2018 2:20 pm

Man, JSSR... you have a genius for elegant designs. I can't see this being practical to build and operate small scale, but it looks like it would be a great design for something like artillery pieces or rocket launchers.
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Re: Twist and Shoot

Unread postAuthor: jackssmirkingrevenge » Wed Jun 20, 2018 3:44 am

One application could be cartridges in a stick magazine, with the trigger basically elevating a cartridge to a barrel... again, not something I'd build at this point but I enjoy these little mental excursions.
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Re: Twist and Shoot

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