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New Pneumatic Powered Cable Gun Design

popgun pete

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Jul 30, 2008
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This design was revealed to me recently by a contact, but I do not know who originated it. At first glance it seems to be a novel way of circumventing the problem of running a cable drive across a pressure boundary in a pneumatic speargun. Some time back we saw a patent for a Mares based cable gun that ran a cable through a pressure seal that would give problems in maintaining the seal integrity over time.
https://forums.deeperblue.com/attachments/cable-pneumatic-2-r-jpg.42914/
new piston pulley gun.jpg


In this design the layout is used which is most commonly seen in inverted rollerguns using moving sub-pulleys on the end of a band battery on each side of the gun or grouped together side by side under the gun's lower deck. Here the bands are replaced by a pneumatic barrel sending a sliding piston rearwards. Now the problem with inverted rollers is the force transmitted to the wishbone is halved because one half goes to the fixed cable anchor at the muzzle, hence the band batteries have to be doubled in size. Basically this is a consequence of the battery power stroke being half that of the wishbone travel. This new gun could retrieve the situation by having a separate pneumatic barrel on each side of the gun, but at the cost of extra weight and complexity.
new piston pulley gun forces.jpg


Another problem is the area of piston exposed to compressed air pressure is effectively a small annulus around the travelling rods shown in yellow, hence the force on the wishbone would be low unless very high pressure was used in the gun. The "Dreamair" by comparison has a big diameter piston fully exposed to pressure and the cable drive uses a spinning axle to cross the gun’s pressure boundary, hence bar losses at the axle and the need to use energy to spin the assembly the forces are directly applied to the gun’s wishbone and not split as they are in this new design.

Note that in the last diagram I have not shown the spear moving, the intent was to show the force splitting.
 
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popgun pete

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The diagrams are annotated in Russian, so if readers from there know the source then perhaps they can tell us who the designer is.
 

popgun pete

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The only way to improve the design would be to narrow where the moving rod connects to the piston in order to enable more surface area to be exposed to high pressure on the piston face. That would involve a narrower rod as any step facing forwards would add to force pushing the rod forwards rather than rearwards. A simple pneumatic gun would outperform this system as is. The advantage of a big piston cross-sectional area is what makes the "Dreamair" gun useful as otherwise such a big piston could not be used in a pneumatic speargun.
 
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Get Sharked

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Wow that is very similar to a design I drew in microsoft paint many, many years ago when I was young, except mine was band powered. I never did anything with it. Just brainstorming for fun.
 

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popgun pete

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These type of guns have been around for a long time, The Roller G is an example and these diagrams are from the patent.
Roller G 1.jpg

Roller G 2.jpg
 

Get Sharked

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I had no doubt that'd it most likely already been invented. It's just nice to mess around sometimes with ideas. Here's another I found with geared pulleys!
 

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popgun pete

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Those pulley gears would be susceptible to getting jammed by something going through the nip, also gearing works against you when cocking it.
 
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