I had to build a potato canon for a science project and needed one where I could get a consistent launch force. The typical hairspray cannon would not be appropriate for this purpose so I constructed this air powered launcher as a modified version of Pnewton's Petard from the excellent book "Backyard Ballistics". Typical results were a range of over 300ft using a weight, nonsealing projectile, I am sure a potato would go much farther.
Step 1: Materials
The materials needed for constructing the air cannon are as follows:
Â·22-inch length of 1Â½-inch diameter schedule-40 PVC pipe
Â·1.5-inch diameter male-threaded PVC pipe adapter
Â·Teflon pipe tape
Â·1Â½-inch diameter female-threaded PVC pipe adapter
Â·1Â½-inch diameter to 3/4-inch threaded PVC reducing bushing
Â·Electric drill with various sized drill bits
Â·1 rubber-coated, narrow-diameter, replacement-tire air valve
Â·2 3-inch-diameter PVC end caps
Â·2 9-inch-long pieces of 3-inch diameter Schedule-40 PVC pipe
Â·3-inch x 3-inch x 1Â½-inch PVC tee connector
Â·3/4-inch diameter short iron pipe nipple
Â·3/4-inch ball valve (It has also been suggested that a pneumatically modded sprinkler valve would allow for a faster and there for more powerful launch. I have no experience with this so for the sake of this article we will use the ball valve.)
Â·3-foot length of 1-inch diameter wooden dowel or broom handle
Â·Foot-stabilized air pump
Below is the diagram and the assembled materials.
SAFETY NOTE: I have received several comments regarding the use of Cellular Extruded Piping. In short - don't use it. It is not meant to deal with air pressure and could explode violently producing hundreds of deadly shards. I have not had this occur yet but if at all possible please use a better piping.
Step 2: Construction
The construction of the launch apparatus (see below for a diagram) is as follows.
Attach 22-inch-long pipe to the 1½-inch male pipe thread adapter using PVC cement.
Attach 1½-inch female adapter to 1½-inch to 3/4-inch reducing bushing using PVC cement and allow to cure.
Screw male pipe thread adapter assembly to female pipe thread adapter assembly carefully.
Drill hole in one 3-inch end cap the diameter of the tire valve. Insert the tire valve into the cap.
Attach both 3-inch end caps to 3-inch diameter pipe with PVC cement.
Use solvent weld to attach the 3-inch pipes to the tee connector.
Take the second reducing bushing and attach the 1½-inch opening to the tee connector with PVC cement.
Wrap the heads of the 3/4-inc pipe nipples using Teflon pipe tape.
Insert the nipples into the ball valve (or as it has been suggested the pneumatically modded sprinkler valve).
Screw the ball valve-pipe nipple into the 22-inch barrel.
Screw the new barrel assembly into the pressure chamber.
Allow to cure overnight.
Wrap the pressure reservoir with three layers of duct tape. (optional)
Step 3: Safety
To test the safety of and seal of the air chamber additional steps must be taken. Close the launch valve and pump the reservoir up to 10 PSI. Sprinkle soapy water on the joints. If bubbles appear, joints are not airtight and you must restart. If no leaks are found, repeat safety step 2 with 30 PSI. When done, aim the barrel in a safe direction and release the pressure.
Step 4: Firing!
The actual act of firing the cannon requires further knowledge. Use extreme caution in aiming device. Make sure all parts are securely attached. Check launch platform after every launch for signs of wear. DO NOT over pressurize the pressure chamber. 30 PSI should be used as a high average. Use ear protection and eyewear. Clear the area in front of cannon for 200 yards. Clear area around cannon for 25 yards.
I used a weighted ping-pong (filled with clay) for my experiment with tissues as wadding. I needed this to have a consistently sized and weighted projectile. I encourage the use of potatoes however as when you jam one down the barrel, they lock it up and nice airtight. That means you get way more range. Moreover, who doesn't like shooting potatoes?
DO NOT shoot pointed, explosive, fragile, or living projectiles. I am not responsible for any of the damage you may incur in such a case.
An angle of 45 degrees should give you the greatest distance. This cannon shoots very accurately and I can consistently land my projectiles within five feet of each other.
See how close you can land to a target and assign points to see who is the best bombardier.
This cannon is tons of fun but can also be very dangerous, remember to use your head and think about what you're doing. I'm not responsible if you put a potato through someone's head...