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Propane Semi Auto Spud Cannon Design Help!

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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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 1:36 pm

ummm, i like your ideas but the torch isnt convincing me, id rather just get a propane adaptor its 7 bucks and il connect it straight to the chamber, plus the thing does have a valave that you unscrew so the propane wont just hiss out non stop.

And why is it bad to have liquid propane in the chamber at such relatively safe pressures?
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Unread postAuthor: Technician1002 » Thu Aug 06, 2009 2:24 pm

spudnutbutthut wrote:And why is it bad to have liquid propane in the chamber at such relatively safe pressures?


Put a piece of PVC in the deep freeze. Then pull it out the next day and drop it on concrete..

Cold PVC is brittle. Propane boils near -44F at atmospheric pressure.
Safety first.
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Unread postAuthor: dewey-1 » Thu Aug 06, 2009 2:44 pm

spudnutbutthut wrote:Id be launching a nerf rocket, around 150 - 200grams i think



A Nerf Pocket Vortex football weighs 30 grams to be a little more accurate!
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 2:59 pm

how much of a chance do i have of getting liquid propane in ther?
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Unread postAuthor: jimmy101 » Thu Aug 06, 2009 3:14 pm

spudnutbutthut wrote:how much of a chance do i have of getting liquid propane in ther?

Based on the valve you intend to use, somewhere between 0% and 100%, inclusive.

If you invert the propane tank then it's 100%. If the propane tank is upright then it is near zero.
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 4:05 pm

will it kill the gun right away?

and me...
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Unread postAuthor: pat123 » Thu Aug 06, 2009 4:17 pm

will it kill the gun right away?

and me...


The gun- most likely

You- probably not, you would just have shrapnel lodged in you. probably not killed but it wouldn't feel good.
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 4:43 pm

should i build this god dammit?
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Unread postAuthor: POLAND_SPUD » Thu Aug 06, 2009 6:07 pm

yeah go for it... just take some basic steps to build a safe launcher...

Normally I would advise to use metal chamber but I am aware that weight might be an issue here so you would have to find something relatively light, preferably aluminium... if you can find something suitable it would be a good idea to use metal on all the parts apart from barrel and the valve... threaded fittings should speed the building process a lot and let you mod the gun in the future


but I suppose you can use pressure rated PVC if you couldn't find suitable metal chamber... however, with PVC you have take into consideration what tech said about cold temperatures


generally the design is rather simple and proven I suppose you shouldn't have too many problems with it
I don't really know why this discussion in on 4 pages already... some people just make you think it's more difficult than it is... safety is an important issue but you can solve almost every problem you face with this gun with the use of a metal chamber

ohh BTW it isn't a semi auto at all... to be a semi it would have to have a loading mechanism... it isn't a crime that you labelled it in the wrong way but it confuses those who want to help you
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 6:46 pm

ah. actually thanks to everyone I was verrry confused at the often very different views on the matter but i have figured it all out. Im gonna use a benzomatic valve with a hose etc. And i thougt about making a magazin. The magazine would be an open top box that gravity feeds rocket into the barrel as the loaded rocket leaves the barrel. It would have a trap door as not to get in the way of the loded shell. The first shell would fall into the barrel, then the door would snap back on a spring until the rocket left!

Im prolly not gonna do that though haha!


THANKS AGAIN!
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Unread postAuthor: ramses » Fri Aug 07, 2009 9:31 am

just make a bolt action breech

granted that one has to be scaled up a little, but just replace all of the 1" pipe with 2" and all the 1 1/2" with 2 1/2".
same with all fittings
so for things besides pipe, you would need:

Small hose clamp for 2" Pipe
Screw and wooden dowel for lock
2 1/2" -2" Bushing x2
2 1/2"-2" Coupling x2
2" to Male thread
Washer, ideally rubber, just under 2.445" OD, ~2" ID
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Unread postAuthor: spudnutbutthut » Fri Aug 07, 2009 12:44 pm

il think about, muzzle losdingbis fun though :]
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