Air Gun
This air gun was a quick project I picked up during my Thanksgiving holiday. The pressure vessel is two three-foot sections of 2" galvanized pipe that I fill to a hundred psi (the gun could take more, but that's the setting of the compressor I'm using). The barrel is a four-foot section of 2" PVC pipe. It took less than four hours to build the gun and the frame.
Currently, my trigger is just a standard ball valve. For best performance, a modified sprinkler valve should release the pressure. The ball valve works well, but it takes a fraction of a second for me to open it fully. That delay represents lost performance. In the future, I'll make this upgrade. I did try using an unmodified sprinkler valve, but I got almost no performance from it (even at 100 psi it produced barely enough pressure to gently nudge the potato out of the tube and onto the ground a foot away).
Using my phone, I recorded a 1/8x speed slow-motion video of me shooting a potato (at a horizontal angle rather than behind like the video below). Then I was able to use Tracker to calculate the speed of the potato as it left the gun. The result was an initial velocity of approximately 70 mph.
