The old potato cannon was a little… well bulky. Whenever I could get it out (required a pickup or trailer) it definitely made a crowd. However, there were just too many times that I wished it were a little more portable so I could take it more places. That spawned this new more portable potato cannon. Still metered propane injected except this time I am using a 950,000 volt stun gun for the ignition with a spark strip. After a day of testing I am very very happy with its performance and reliability.
The barrel is actually rifled just like you would see inside a rifle. It was purchased several years ago by me from www.SpudTech.com which has some great products. The chamber size was calculated around the size of the barrel since I already owned it. Using various online calculators I determined the needed size of the chamber and metering tube for the propane.
A regular pc fan is used inside the chamber to vent out the burnt air after each shot and to circulate the propane to evenly mix it. I did not have this setup the first day I used it, so comparing with and without, I would highly recommend a fan inside. Also you can see the pcb board that creates 8 spark gaps for the stun gun. On the right side is a 3″ piece of pvc pipe which holds the propane tank and a project box from RadioShack. On top is the metering tube for the propane injection. This propane injected stun gun / taser fired potato cannon is quite efficient. 3 bags of potatoes and 0 misfires.
Here is a side shot of the chamber with the barrel removed. To fire the gun you attach the barrel (screw it on) insert potato in the end of the barrel and pack it down to the bottom of the barrel where it meets the chamber. Next you turn on the fan to vent the chamber and put the cap on the end of the chamber to seal it off. Turn the valve on the propane tank on and watch the pressure gauge as it pressurizes the hose. After turning the first valve to fill the metering tube wait for the pressure gauge to climb back up to about 75-80 psi (propane tank supplies 90psi) then turn off the valve. Now turn the chamber fan back on and release the propane into the chamber using the valve on the other end of the metering tube. Arm the ignition by turning on the switch on the far left and you are ready to fire.
I am in the process of making a chronograph to measure the muzzle velocity of the potato cannon. This prototype failed to work at the speeds the potato(s) was going.
Basically it consists of two photo resistors one foot apart. As the potato passes by it blocks light and that reading is calculated by an Arduino Microcontroller and fed back to my laptop.
A simple chair with some plywood served as the base for the chronograph with another piece of plywood to keep direct sun off of the device.
After three shots the chronograph never got a reading so shooting the plywood let out some frustration. Before first shot.
After the first shot. The rifling causes the potato to come out a little up and left. However, it stays very very straight after that due to the spinning caused by the rifling.
Second shot knocked everything down and went right through the 1/4″ plywood at a distance of ~20ft.
Back side of second shot and front side of third shot.
After only a handful of shots the plywood is decimated.
Sample video showing plywood destruction and brief operation description.