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Need help with finding a cheap cannon to make

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: myself123 » Thu Aug 27, 2009 12:21 pm

Willdebeers wrote:Do you work with imperial or metric?

We use metric, but can always calculate :)
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Last edited by myself123 on Thu Aug 27, 2009 12:21 pm, edited 1 time in total.

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Unread postAuthor: qwerty » Thu Aug 27, 2009 12:21 pm

im guessing MM do you get things like 15mm copper parts and 22mm copper parts or 1 inch and 1/2 inch
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Unread postAuthor: Willdebeers » Thu Aug 27, 2009 12:27 pm

He said metric. Ok, i'm metric too, but I just thought you were american, so I used imperial. In that case, try a simple copper cannon. They can take vast pressures (500-600 psi) and are quite simple also. You can also use a QEV to trigger it, which improves results greatly.
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Unread postAuthor: qwerty » Thu Aug 27, 2009 12:30 pm

then a basic CHAMBER-------BALLVALVE----BARREL-----------------------gun
:)

BTW will do you wanna go on the chat?
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Unread postAuthor: myself123 » Thu Aug 27, 2009 12:37 pm

Hmm, what nipple can i use to fill it with? Cant use those car valves, we got those tiny air hoses and thats about it
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Unread postAuthor: Willdebeers » Thu Aug 27, 2009 12:38 pm

yeah sure qwerty. Oh and just use a quick disconnect fitting.
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Unread postAuthor: myself123 » Thu Aug 27, 2009 12:41 pm

Willdebeers wrote:yeah sure qwerty. Oh and just use a quick disconnect fitting.

Which is what? :p Googled it, but how do you keep the air inside then? doesnt it need to be a one way valve? or do you mean to use those on the car tire valve?
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Unread postAuthor: jimmy101 » Thu Aug 27, 2009 12:44 pm

myself123 wrote:Image
I tried to make a quick idea in paint for a small gun, would this work?
The nipple is for one of those small air hoses, so i can connect it at school to fill it. How big does the tank thing need to be? And what do i need to make it so it can hold 100psi?

Yep that'll work. The performance won't be spectacular but it'll still be impressive enough.

The inlet ball valve isn't needed if you fire the gun while still attached to the compressor's hose.

Or, instead of the nipple and ball valve for the inlet connection you might consider a Schrader valve. (A Schrader valve is the valve on a bike or car tire.) You should be able to get a metal Schrader from a car tire store or decent car parts store for about a buck. Your compressor hose will need to end with a standard tire filling chuck. The Schrader is a valve so the ball valve is no longer needed. The disadvantage of just using the Schrader valve is that you'll probably need to remove the stem while ramming the spud into the barrel; the air in the gun has to have some way to escape as the ammo is rammed.

Pressure rated PVC will be fine with 100 PSI as long everything is glued properly. Read the SpudWiki pages on PVC solvent gluing and how to identify pressure rated pipe and fittings.

There is a huge range in what dimension you might use. The first decision is probably "what are you going to use as ammo?" That'll determine a suitable barrel diameter. Hunks of spud (zucchini, apples ...) are pretty cheap ammo and would be less likely to cause alarm at the school. After all, how much damage can a hunk of spud do? (Actually, it can do a hell of a lot, in the right gun more damage than a 0.22 cal rifle bullet, just don't tell anybody that :D ) For veggies a 1" or 1.5" diameter barrel would be a good start. A 2" barrel will work better but it takes big and expensive veggies to fit a barrel that size.

A two or three foot or so barrel will be small enough to hold so that would be a reasonable length to try.

The chamber should be made out of the largest diameter pressure rated pipe and fittings that you can find. With luck you can get 3" pipe and fittings, more likely your local hardware store will only have pressure rated stuff up to 2" diameter. 2" is OK, it just means the chamber will end up being about 2X longer than it would if you could get 3" pipe.

The length of the chamber should be ... depends on what you want. Assuming you are going to hand-hold the thing while firing then the chamber can't be too long. A chamber volume equal to the barrel volume would be reasonable. A chamber twice that big would be a bit better. Since you've already chosen the barrel ID and length, and the diameter of the chamber, just do the math for a 1:1 or a 2:1 ratio between chamber volume and barrel volume.

Since you are clearly new to spud guns it is important that you realize how much energy is in the pressurized chamber and how much energy the gun might transfer to a shell. These things are not toys, they are not Nerf guns or BB guns. If you have a catastrophic failure of the chamber when it is charged to 100 PSI it may well remove a finger from your hand or turn an eyeball into an unusable hole in your head. A hunk of spud fired from the gun may well have lethal levels of kinetic energy. If you fire something sturdier than a spud, like a golf ball or saboted nail, it will definitely have lethal energies. Be safe.
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Unread postAuthor: Willdebeers » Thu Aug 27, 2009 12:49 pm

myself123 wrote:
Willdebeers wrote:yeah sure qwerty. Oh and just use a quick disconnect fitting.

Which is what? :p Googled it, but how do you keep the air inside then? doesnt it need to be a one way valve? or do you mean to use those on the car tire valve?


You use one of these> http://en.wikipedia.org/wiki/Check_valve
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Unread postAuthor: covey12 » Thu Aug 27, 2009 5:13 pm

2" end cap to about 2ft. of 2" pipe, 2" ball valve (or reduce it to atleast a 1") then about 3 ft of what ever diameter barrel you want, this is the first, and most reliable i have ever made
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Unread postAuthor: MrCrowley » Thu Aug 27, 2009 11:01 pm

covey12 wrote:2" end cap to about 2ft. of 2" pipe, 2" ball valve (or reduce it to atleast a 1") then about 3 ft of what ever diameter barrel you want, this is the first, and most reliable i have ever made

Remember he's in Norway and might not be able to get PVC as easily as in America...
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