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Small caliber spud gun/ Nerf gun

A place to ask general spud cannon related questions.
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Unread postAuthor: jackssmirkingrevenge » Tue May 17, 2011 4:43 am

Stormling wrote:The thing said that the barrel was unnecessarily long too.


That was because the dwell time was miniscule, coupled with the low pressure. If you're squeezing a blowgun trigger, it will be open for at least half a second.
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Unread postAuthor: Stormling » Tue May 17, 2011 4:44 am

Ok so I've tried longer barrels (70 cm, do I need longer?) and Upped the pressure to 45 psi (30 psig in the program) but it seems that the projectile simply travels the length of the barrel with some strangely fluctuating velocity
Right now am I better of ditching the design I have (using a pressurized chamber and shooting 'squirts' of air from a blowgun valve to launch the darts) or starting again with a whole new design.
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Unread postAuthor: jackssmirkingrevenge » Tue May 17, 2011 6:04 am

Stormling wrote:Right now am I better of ditching the design I have (using a pressurized chamber and shooting 'squirts' of air from a blowgun valve to launch the darts) or starting again with a whole new design.


I think the blowgun design will serve you well.

Try modelling with the following parameters:

generic valve, opening time 20ms, dwell time 750ms, seat diameter 0.4cm, dead volume 2cm<sup>3</sup>

barrel: 50cm length, 1.27cm bore

projectile diameter 1.27cm, weight -> weigh ten of your darts on a kitchen scale or similar and divide by ten.

chamber: 75 psi, easily reached with a bike or foot pump, dimensions outer dia 5cm, inner dia 0, length 25cm, this gives you about the same volume as a 2 litre pop bottle which would make an idea cheap chamber perfectly safe at 75psi.

Let us know what results you get.
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Unread postAuthor: Stormling » Tue May 17, 2011 6:31 am

jackssmirkingrevenge wrote:
Stormling wrote:Right now am I better of ditching the design I have (using a pressurized chamber and shooting 'squirts' of air from a blowgun valve to launch the darts) or starting again with a whole new design.


I think the blowgun design will serve you well.

Try modelling with the following parameters:

generic valve, opening time 20ms, dwell time 750ms, seat diameter 0.4cm, dead volume 2cm<sup>3</sup>

barrel: 50cm length, 1.27cm bore

projectile diameter 1.27cm, weight -> weigh ten of your darts on a kitchen scale or similar and divide by ten.

chamber: 75 psi, easily reached with a bike or foot pump, dimensions outer dia 5cm, inner dia 0, length 25cm, this gives you about the same volume as a 2 litre pop bottle which would make an idea cheap chamber perfectly safe at 75psi.

Let us know what results you get.


Getting no warnings and no errors on GGDT. Gonna give this thing a burl when a get the parts. I'll probably make a tank just so I can get better fitting on for a shraeder valve. I'll get back to you when it's done.
Thank you for your help and I apologize for any badgering I have done.
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Unread postAuthor: jackssmirkingrevenge » Tue May 17, 2011 6:36 am

Good luck with it :) remember, if in doubt, epoxy ;)

Stormling wrote:Thank you for your help and I apologize for any badgering I have done.


No worries, we have no quarrel with those who genuinely seek knowledge and are willing to listen to good advice.
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