What is a potato launcher?

A potato cannon (also known as a spud gun) is a pipe-based cannon which uses air pressure (pneumatic), or combustion of a gaseous fuel, to launch projectiles at high speeds. They are built to fire chunks of potato, as a hobby, or to fire other sorts of projectiles, for practical use. The projectile can be dangerous and result in life-threatening injuries, including cranial fractures, if a person is hit. (http://en.wikipedia.org/wiki/Spud_gun)

This instructable shows the steps I took in order to construct my potato launcher.

This project was inspired by the Mythbusters soda can launcher featured on their commercial. Unfortunately theirs was big and bulky I wanted something that closer resembled a rocket launcher, which is how I arrived at my Pneumatic potato cannon.

Disclaimer: Read this instructable at your own risk, under no circumstances should anyone attempt to recreate this extremely dangerous project. I accept no responsibility for any injuries or damage that may occur. DO NOT TRY THIS AT HOME. :)

Step 1: The Design

There are two main types of potato launchers: "Pneumatic launchers" and "Combustion launchers"

- Combustion launchers generally use the explosion force of a combustive fuel to propel a potato at very high speeds.

- Pneumatic launchers are more complex and use the force of compressed air released into the barrel to shoot a projectile.

I decided to go with a Pneumatic launcher because it seemed like it would be safer and more reliable. It turned out to be very reliable but more dangerous than I had expected...  think "vaporized potato at point blank on concrete." I also needed a reason to buy an air compressor but don't tell anyone.

To avoid ending up with just another Pneumatic launcher with a separate tank and barrel with a valve between them, I decided to put the barrel inside of the tank. This would also make the entire launcher self contained and possibly more durable, as expected it also makes this launcher really frustrating to put together. When its finished the tank will be the pressure bearing area between the body and the barrel.

If your looking at the diagram, each piece will show a caption if you hover over it with your mouse.
I really dont think that counter-sinking the places where you tapped the fittings in is a good idea. It seems like it would greatly reduce the safety of the gun.
I agree if there is a version 2, there will not be any countersinking. Still I have dropped the launcher on its side and the holes have held up so far, broke the gauge though.
That is scary. I personally wouldn't use it after giving it a shock like that. I usually cover my cannons with pipe insulation to protect it if it bash it on anything.
When you pressurize this, is the entire 4-inch pipe under pressure or is there an inner chamber I'm not seeing?
Your correct, when fully assembled the entire 4" diameter PVC pipe is under pressure. Although it's not recommended by the pipe manufacturer, it seems to be fairly safe being well under the maximum pressure.