THIS IS WHAT IM GONNA MAKE
Construction is simple. The cannon consists of a combustion chamber fitted to a barrel of smaller diameter. Our basic theory is that the combustion chamber should be large so as to produce a large volume of gas during the combustion, which will be forced at high velocity through the barrel, propelling our projectile.
combustion chamber length:14 inchescombustion chamber diameter:3 inchesbarrel length:36 inchesbarrel diameter:2 inchesmuzzel velocity:80 mph (estimated)range:100 yards max
Materials are all common and can be purchased for a small sum at your local hardware and grocery stores.
10 foot length of 3" diameter schedule 40 ABS pipeHome Depot$8.5510 foot length of 2" diameter schedule 40 ABS pipeHome Depot$4.253" to 2" reducing coupler, ABS schedule 40Home Depot$2.573" threaded (one side) coupling, ABS schedule 40Home Depot$2.673" threaded end capHome Depot$1.38small can of ABS welding cementHome Depot$1.71Coleman Lantern ignitorSport Chalet$3.99Trigger-style butane/piezoelectric barbeque ignitor (see photograph)Ralph's10.5 oz Aqua Net hair sprayRalph's$1.63Russet PotatoesRalph's89¢/lb
No special purpose tools are need for construction.
Hacksawto cut the ABS pipingFileto taper the muzzle so that it can cut potatoes to size when we jam them inDrillto drill hole for ignition mechanismHair dryerto ventilate the exhaust from the system
Just a few comments on instructions: Every few days, someone emails me asking for ``detailed instructions'' on potato cannon construction. I have no more detailed instructions than the diagrams given above, which should supply all the information needed to get started. Part of the fun of building such a thing is experimenting with the design. Furthermore, I have a feeling that if someone is not able to build a cannon given the above diagrams, then perhaps they shouldn't be building a cannon at all (I don't want anyone to hurt themselves by following step-by-step instructions without a clear idea of what they are doing).
I do have a comment on the ignition mechanism
. Originally we used a flint-and-steel Coleman lantern lighter. This is a little assembly that produces a shower of sparks with a quick twist of a knob. We mounted the lighter through a hole drilled in the side of the combustion chamber. Unfortunately the flint/steel assembly doesn't hold up well to repeated firings, and failed pretty quickly. As a replacement, John and Eric discovered that a trigger-style barbeque lighter
works amazingly well. This is sort of like a cigarette lighter, except with a trigger that produces a piezoelectric spark. The barbeque ignitor can be inserted through a hole in the combustion chamber as seen in the photograph above. It helps tremendously if the ignitor forms a tight seal with the hole; use ABS cement and maybe some duct-tape to form such a seal.
Many people ask me whether something is necessary to "prevent the potato chunk from falling into the combustion chamber." Once you build a cannon you will quickly find the answer to this question yourself. The fact that the design given here does not reference such a component should be a strong clue.