air cannons


Here are some air cannons that I have built. Also known as spud guns, as they are usually meant to shoot potatoes, these devices are made primarily of PVC pipe and shoot objects using compressed air. These devices are inherently dangerous due to the tremendous energy stored within the air chamber, and the substantial speed at which it discharges projectiles. If you wish to build or operate your own, do so at your own risk.






mark I



This is the original air cannon. Its air chamber, made of 2" SCH40 PVC pipe, doubles as a base. The chamber is filled via a Schrader valve glued into a 2" cleanout cap in a cleanout tee. Two parallel 1" sprinkler valves can be triggered to dump the air into a 7' long 1" barrel. Due to some design flaws which made it annoying to set up and use, it is no longer used. Most importantly, the long and thin barrel flops around and must be supported along its length. It is also difficult to aim in the vertical direction without someone holding the cannon in position. Its small barrel does not allow a wide range of projectiles. However, its performance is not affected by these factors and has, on occasion, been impressively powerful. C batteries fit the barrel perfectly, and metal rods can be fired with a thick disk at the end and some toilet paper as wadding.

chamber Here is the main body of the cannon, with the barrel attached. Yes, it has 'Lu Laboratories' and related text written all over it. You can see that the primer job was rather messy.
valves Closeup of the twin valves. Two valves are somewhat better than one due to the greater cross-sectional area that air can flow through. Even though the valves have 1" diameter porting, the actual open area is smaller. Unfortunately, due to the way this was assembled, it is impossible to remove the valves without sawing off some PVC.
projectiles These projectiles were used in the Mk I cannon. The white plastic piece in the lower right corner is the sabot, or pusher, for the rods at top and left. The bit sticking out of the ends of the metal rods fits into the hole in the sabot.
bottle Lu Laboratories has a tradition of attempting to destroy objects known for their durability or toughness. Here, a Nalgene water bottle, full of water, is about to receive a metal rod.
bottle with hole The aftermath of the previously set up shot. The projectile went through the bottle entirely and embedded itself in a fence some 40 feet away.
bottle with rod The same Nalgene bottle, with the projectile inserted to show how it went through.
power supply An old Macintosh power supply after being shot with a random metal slug. It punctured the power supply, but the coarse threads on the shaft prevented it from clearing it.
power supply The same power supply, showing how the projectile went right through the fan.

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mark II ('type H')



This aircannon is a tremendous upgrade from the first one. It features a 9' long, 2" diameter barrel, and 10' of 4" pipe for a chamber. It uses a piston valve built into the 4" cross. When pressurized, the pressure on one side of the piston counteracts the pressure on the other side and seals it against the barrel. The sprinkler valve protruding from the end releases the pressure from one end when triggered, allowing the pressure in the chamber to force the piston back and open the valve. Obviously, the piston would slam into the cleanout cap with significant force, were it left unchecked. Two pieces of tubing were bent into circular shapes and hot-glued into the end to prevent this. The barrel had a sharp edge at the muzzle end designed to cut potatoes to the proper size to be fired. The barrel was meant to have supports to prevent it from straining the connection to the cross, but they were never made.

diagram A diagram of the Mk II air cannon. It is not a measured drawing or any such thing; it is meant to show how the device is put together.
piston valve A diagram showing how the piston valve works. Again, not a measured drawing.
piston valve A 3D rendering of the piston valve assembly. The sprinkler valve (not shown) goes on the end of the protruding piece on the far left.
piston This is the piston. It was made from a 3" PVC coupler, a wooden disk, a metal disk, a 2" fender washer, a bolt, and some rubber. It performed decently. This picture was taken before the bolt, washer, and metal disk were added to improve strength.
piston The other end of the same piston. The hole is there to allow air to pass and fill the chamber; it is covered by a rubber flap on the other side that does not permit air movement in the other direction. We suspect that the gap between the piston and the cylinder was responsible for more leakage than this hole could ever have been.
cannon The cannon itself. It is rather large and unwieldy. The cardboard tubes were there to help contain a potential explosion, but more to placate some bothersome people worried about safety. Fortunately no explosion ever occurred, as the cardboard would probably do little to nothing to contain it.
cannon A potato shot at 40PSI or so. You can see it flying toward the concrete barrier, where it will become a cloud of potato mush. Unfortunately, there are not many photos of operation or results, and the cannon was given away some time ago.

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mark III ('mini-H')



The latest air cannon, the Mk III, is a relatively portable aircannon meant to be carried by a person. It features a 3' x 4" chamber, and a 5' x 2" barrel. The piston valve is an improved design that fills more quickly and seals better than the one in the Mk II. The size and shape allow it to be easily carried, thus eliminating the setup necessary to position and aim the earlier cannons. A new projectile was developed for this cannon, based on modern anti-tank rounds. Stainless steel guide rods from scanners and printers are sharpened to a point, then fitted with fins. A steel disk is placed at the end as a pusher, and pieces of foam cut from a pool noodle are used to keep the rod centered. An improved sabot is being designed, based on the spindle sabots used on actual anti-armor rounds.
cannon The Mark III. The design is simple. The parts are all fairly obvious and the valve assembly is almost identical to that of the Mark II.
extension We decided a 5' barrel was not long enough, so this was our solution: a 10' segment of 2" PVC to be coupled on to the end with that rubber coupler. Calculations indicate that this should provide two to 2.5 times the output energy. The coupler is soft, which makes alignment problematic. This will eventually be fixed with some bracing or a mount.
sabot diagram A CAD drawing of how the new sabot will go together, and what each layer looks like. It is made of thin metal disks separated by plastic disks, all bolted together. The metal disks have a smaller inside diameter and thus grab onto the barbs on the projectile.
projectiles A couple of rods we shot through various things. The bent one ended up that way after travelling through a hard drive, a CD-ROM drive, a computer, and a book, finally hitting a tree while spinning and deforming the rod. It has grooves cut into the tip such that it resembles a Phillips screwdriver. The bottom one has no such grooves and we suspect penetration is decreased because of it.
hard drive This is a hard drive shot with a rod using the '+1' barrel extension. Priority Mail stickers were used as tape to hold the drive to the target stand.
hard drive Disassembling the hard drive reveals that the rod went through the front cover, two platters, the back cover, and the circuit board. Note the four-pronged burr on the hole in the front cover, suggesting that the four grooves cut into the tip of the projectile performed as expected and produced a sort of cutting action on the plate.
hard drive This is another hard drive, shot twice with the same projectile. This drive was somewhat tougher than the previous one, with a steel front cover and three platters instead of two. The first shot struck approximately the same place as the shot on the previous drive, again penetrating the entire drive. The second shot struck the voice coil magnet, shattering it and tearing apart the magnet's backing plates, and breaking the entire drive casing in two.
hard drive Here is a closeup showing damage to the platters and other internal components.
hard drive A computer case after being the recipient of several rods. This was the backstop against which our targets were placed.


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