Lu Labs' Air Cannon!
An air cannon is a device used to propel objects at immense speeds using compressed air. People have built large air cannons that are able to shoot potatoes many miles; however, I have decided to start with something smaller.
A Word About Air Cannons
My cannon consists of an air chamber, dual sprinkler valves, and a barrel. The chamber is formed into a shape that acts as a base for the entire cannon. It is made of 2 inch sch 40 PVC pipe, able to take 280 PSI (though the valves will only take 125.)It has a cleanout plug and a tire valve in the plug to allow filling with compressed air either from a bike pump or an air compressor.
The valves are standard 1 inch Orbit sprinkler valves found at Home Depot. They are a solenoid-actuated diaphragm type (for a drawing of the valve insides see here.) I have yet to make any modifications to them, but once I do, they should activate much faster. The valves are connected in parallel, allowing more air flow.
The barrel is a piece of 1 inch sch40 PVC pipe 80 inches long, with a
female thread at the end allowing it to come off the chamber and valve
The old projectiles are the two steel rods shown above. The short
one with threads about 3/4 up its length is not so great as a
projectile as the threads get stuck when it penetrates the target. The
long steel rod with thin parts at both ends is also not excellent due
to the fact that the ends catch and do not penetrate well. I will
machine a sharper tip on one end of the long steel rod. The white
chunk to the side is a piece of Delrin for use as a sabot (to fit the
projectiles snugly in the barrel).
All of my projectiles. You can see that the two long steel rods have
tips machined on them now. The C battery is also used occasionally,
for shooting some things.
The most I've pumped the aircannon up to so far is 50psi. I am too lazy to stand there pumping the bike pump up to more than that :) I really need an air compressor. For most targests, 20-40psi is enough to cause quite a bit of damage. 20psi is enough to shoot a steel slug through 1/2 inch plywood.
I can't remember all of the things I've shot, but here is a partial list and the results:
- 1/2 inch plywood: both with a C battery and with a steel slug. Both penetrated rather easily at 20-30psi. These tests were done indoors, not a smart idea but it was too cold to go out.
- Patio brick: I found this laying around, it was left over from when we made our patio.When hit with a C battery at 30psi it broke into three pieces.
- Old Macintosh computer: Basically, it was hit three times, once in an empty spot, once in the motherboard, and once in the harddrive. The
computer came apart rather easily :) NEW: Pics
- Nalgene water bottle: A orange/yellow nalgene bottle (disgusting color if you ask me) was hit twice, the first time with a C battery at 40psi and the second time with a steel slug, also at 40psi. The bottle has to be filled with water so it has enough mass and doesn't go bouncing away when you hit it. The first shot blew off the cap and made a nice fountain of water, but the bottle itself was undamaged. The steel slug smashed through two walls of the bottle and was stuck. It was a pain to get out later, but I decided to keep the bottle as proof of their breakability :)
- Plastic liquid containers: A couple milk jugs and a 2L soda bottle, all filled with water, were sequentially subjected to the impact of the steel slug fired at 30psi. The two milk jugs weren't very interesting; the slug just "ignored" the bottle and proceeded to slam into my backyard fence and knock boards out. The soda bottle was tougher and more interesting: it sheared in half from the impact and there was a big explosion of water.
A couple of times, I filled the barrel of the aircannon with shredded paper from the paper shredder. When shot out at about 20psi it makes a very nice spray of confetti. Often, you will get a stream of confetti since a wad of shredded paper travels quite far while shedding some of its mass along the way :)
A Word About Air Cannons
Before you even THINK about building one of these things be sure that you know what you are doing and that you know that the air chamber could explode at any time, showering you with PVC fragments. I would use sch80 pipe, and derate to 50 percent rated pressure. Derating less than 30 percent is asking for PVC chips to be propelled into your forehead. Have fun, but be safe and don't be stupid. And above all, don't come crying to me if you get landed in the hospital. You have been warned.
With that in mind, remember that this, like lots of other things, has the potential to eat out your pocketbook very very fast. For a small air cannon like mine it cost over 60 dollars to build, and I already had the 2 inch PVC pipe for the chamber. Please be mindful of the cost when building something like this. Don't let it end up like my Tesla coil, costing over twice as much as expected. It's amazing how many fittings this took to build.