phumatic spud gun

[hardr0ck68]

ok, well the 4th of july is quickly comming, and last year my hillbilly neighbors were so proud of their idiot son's engineering of a spud gun, now while i was watching them i couldent help but think that igniting hair spray cannot produce more than 300 psi (if anyone knows for sure, please tell me, it would help lots)....so i wanna build a spud gun that runs off co2 (or compressed air...doesnt really matter)

2 questions:
will 700 PSI (from co2) be enough to send a tato flying? (and if so how far/fast)

should i use 1 valve/ tank/ inlet or do you (like my partner in this) think that one line will not flow enough air and i should use 2 valves/ tanks/ inlet holes?

im not a physics guy (i understand it, but do not enjoy figurin it out) if anyone wants to figure out how far 700 psi will send a 1lb or so tato (figure 30" umported steel barrel 2.5" diameter) it would be very nice...

[ZapTheMad]

I don't think the flow available from a pin valve is going to get 700 psi behind a potato.

[ScatterPlot]

OK For a pneumatic gun, you'll need an expansion chamber. PVC is rated at like 125 PSI max; don't just put 700 into a chamber to dump. That=bad. You gotta make sure you know when to turn off the valve. In other words, you could have a tank connected to a reg that would stop filling the dump chamber at like 100 PSI or maybe a little more. You could maybe have a gauge that would let you know when the pressure in the chamber reached 100, and then turn off the dump chamber/co2 tank valve. A ball valve or certain types of lawn sprinkler soleniod valves can let you dump the dump chamber into the barrel. There's a ton of websites about this kind of thing, you can Google it if you want to. I've never made a completely successful one (been having some trouble with seals) but it's just a problem with my designs.

[hardr0ck68]

im gonna use 1 or 2 ball valves from a co2 fillstation, i ditched pvc for steel (exaust pipe...) but yeah are you saying that 100 psi will be enough? i would rather skip a dump chamber...(i dont have any expansion chambers layin around) So you think braded steel wont flow the air quick enough??

[ojhspyro89]

Hairspray makes about 30 psi max, thirty.


Dude if you have a good valve design and such you can send a golf ball about 1000 feet easy on 100 psi. ive done it myself.

Go to home depot and go to the gardening department and ask for a Sprinkler Valve. It should have 1" or 3/4". then go to the pvc place where all that stuff is and pick up some glue and cleaner. Get some reducers and such that will reduce for your barrel and chamber. heres and easy list for a cannon that will look somewhat like a long tube like thing. Itll just be strait thru.

1. Sprinkler Valve
2. 2 1" Thread adpters
3. 1-1.5" reducer bushing
4. 1.5" Bushing
5. 1-2" reducer bushing
6. 2 inch bushing
7. 2" endcap
8. shrader valve (tire fill valve)
9. 2" by X amount of feet pvc pipe depending on what u want (IF IT DOES NOT HAVE PRESSURE RATING DONT BUY IT)
10. Section of 1.5" PVC for barrel

For the shrader if you dont have an 1/8" NPT tap, just drill a 3/8" hole in the endcap and force thread the shrader into the cap.

With this gun you will only need a foot pump, beleive me itll shoot pretty darn well for a foot pump. Its an easy gun to build thats fairly powerfull.

DO NOT HOOK UP YOUR CO2 TANK TO THIS GUN, ITS JUST A DEATHTRAP JUST LIKE A PINTO!!!!!!!!!!!!


Im hoping you know how to glue pvc good. Just clean the parts first, then slop on some glue and when inserting peices together, twist and push at the same to to spread the glue. The Sprinkler will need batteries and a switch but thats pretty cheap.


Thats about it AIM me at ojhspyro89 if you need anything else.

[hardr0ck68]

yeah i have done alot of reading tonight...flow rate seems to be the biggest issue, i just figured add more presure...but as i read that doesnt seem to work. This whouldent take to long to build....

[ScatterPlot]

When I said expansion chamber I just meant a length of tube that goes after the bulk tank and before the barrel. Not like a pball ex chamber, I just called that a chamber that the HP air will expand into higher volume LP air. Dunno about metals, never used those. I've tried it with no ex chamber, doesnt work (I used a 12 gram though). With the dump chamber and all it should work awesomely.

[ojhspyro89]

The longest part of building is waiting for it to dry. You can assemble a gun like the one i said in like 10 minutes max. Ive done it before but ended up trashing that gun to make a bigger one!!!!!!!

The title is bugging me " Pneumatic " <----------- Spelling

[WickeDKlowN]

Time to dig up Butterfingers' old thread...

http://www.automags.org/forums/showthread.php?t=22668

[Mole1119]

I built a 50 ft potato gun in highschool. It was pretty wild it had a 10ft by 6in diameter air chamber that dumbed into a 40 ft long by 1.5 in barrel. Shot some watermelons and man did they just vaporize. Using some velocity instrumentation the muzzle velocity was about 650 fps using about 75 psi. I charged it up to the rated the pressure rating on the airchamber pipe which was about 150 psi I belevie but didnt get a muzzle velocity becuse i shot the instrumentation and destroyed it. It was a pretty cool highschool project.

[ojhspyro89]

What kind of valve where u using?

[WickeDKlowN]

I want to build something like that 'Chicken Gun' on Myth Busters...

[Mole1119]

i used an inch and half pvc ball valve

[syko2102]

Are you planning on welding the exhaust pipe or just using some good glue? While I didn't read the post all that carefully I saw something on the mythbusters gun, and I remember them saying something like it didn't matter whether they put 100 or 150 psi into the pumpkin chunker the pumpkins still went as far. As far as getting the potatos to fly far, I heard butterfly valves work best if you can get a hold of one.

PS I will also be using my combustion one on the 4th, makes a great flame a the end at night

[Green_kat]

http://www.totse.com/en/bad_ideas/guns_and_weapons/index.html

got a bad idea, this site can usually help. I think there are several tater cannons in there. as well as the cement filled beercan mortar .


specifically:

http://www.totse.com/en/bad_ideas/guns_and_weapons/spudshot.html

CAUTION: The pipe should be clearly marked SCH-40 260 PSI. ACCEPT NO SUBSTITUTIONS or you will be reinventing the pneumatic hand grenade.

and a discalimer for myself: This is your idea, don't sue me.