Measured Against Reality

Friday, September 22, 2006

How to Build a Pneumatic Cannon

My favorite backyard project is the pneumatic cannon. It’s simple, cheap, and very effective. Here’s how to build one.

All that you need is PVC parts, PVC cement, and a car tire valve. Some plastic epoxy is also a good idea, to help seal the leaks.

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How you build it is up to you, but I like the basic T-shaped design shown here. It’s simple, I find it ergonomic, and it works pretty well. The back end is 3-inch, with two end-caps and a T-connection that narrows to 1.5-in. One of the end caps has to have a valve in it, which can be done by simply drilling a hole and shoving the valve through it. I find that this seal is never very good, and covered mine with the plastic epoxy on both sides. It’s also a good idea to epoxy every joint on the pressure chamber, because PVC cement almost inevitably gets leaks.

The pressure chamber is then connected to a 1.5-in valve, and at its simplest, a 1.5-in barrel that’s a couple feet long, which is perfect for shooting potatoes. I built another gun with that setup, and it can shoot a potato well over a hundred yards, at least by my estimation.

The one shown is more complicated. The valve is attached to a threaded PVC piece. This lets you change out barrels. The one shown is a triple 1-in where two can be open or shut, so it can fire 1 to 3 shots at once. It gets the most distance with only one, but it’s only marginally better than all three. This gun shoots bouncy balls (which have a diameter slightly less than 1-in).

Another good thing about these guns is that they’re pretty accurate. At one point I secured the bouncy-ball shooter to a table, and two consecutive shots went through the same hold in my target. It’s a bit more challenging to aim when you’re holding it, however. They can also be used as water cannons. When they shoot a barrel full of water, it goes about 20 yards and spreads into a nice cloud. Very good as heavy artillery for water fights, except that they’re pretty slow to reload.

And that’s all there is to it, happy building!

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