Construction Pictures:

(Most of these pictures are low-resolution. We do not think very high resolution is needed for these, but if there is enough of a demand for them, we'll post high-res ones.)

Parts and Pieces:

The Pipe:
We use 1.5" diameter PVC Schedule 40 pipe. As seen in the picture, it is rated to 330psi of pressure at 73F (at colder temperatures the pipe can become brittle). The pipe will be cut into two pieces: 1) The pressure chamber where air pressure is built up, and 2) The barrel where the potato will be accelerated by the release of air pressure from the pressure chamber.

Endcap:
This is the place we pressurize the gun from. We drilled a hole in the cap and screwed in a tire valve. The cap is attached to the very back of the gun (the pressure chamber).

Inside the end cap. You can see the rubber seal on the valve.

Valve:
The valve holds the air in the pressure chamber until we want it to release. The valve is attached to screw fittings which were cemented to the pressure chamber and barrel. It is a PVC ball valve, rated to 150psi, the weakest element in the gun. The internal diameter of the valve is the same as the pipe, which allows the air to escape the pressure chamber with minimal air friction.

Barrel:
The barrel is where the potato gets accelerated. The tip of it will be sharpened so that a potato shoved down it is cut smoothly to the diameter of the pipe.

Back to Pictures

Theoretical and Engineering Stuff:

There were a number of issues invovled in the design. Firstly, we needed to determine the best lengths for the pressure chamber and barrel. This invovled some physics (for those interested, a rough draft of our physics work can be seen here). Next we needed to measure the kinetic friction between the potato and the side of the barrel. We measured it by sticking a potato at the top of the pipe and hanging weights from it. When the potato was pushed, and the weights (and attached potato) fell down at a constant rate we knew that the amount of weight pulling down was the same as the friction holding it up. Then we weighed the potato together with the attached weights. Also, we had a maximum total length. We wanted the gun to fit in our father's car. We measured, and the maximum length of the thing needed to be eight feet or less.
Eli and Yoni finishing off the theoretical calculations.

Weighing the friction stuff on Aryeh's postal scale.

And in the end - it fits in the car!

Back to Pictures

Assembly:

As mentioned before, we sharpened the barrel tip. We found it easiest to drag it along the ground, and only after the pipe was mostly worn down to use a file to smooth it out. After all the theoretical stuff was finished, we knew the length of the pressure chamber and the barrel and then could start cutting. We attached the endcap and screw fittings to the pipe with a PVC pipe primer and cement. This was particularly nasty stuff. We'll post all the warnings on the container some point later. After priming and cementing, we let the stuff harden overnight. The next day we spread Teflon "goop" (a screw fitting pipe joint sealer) on the screw fittings and screwed them into the valve.
Yoni sharpens the barrel (doesn't he look evil with those red eyes?).

Aryeh finishes off the sharpening with the file.

Aryeh makes careful measurements.

After Aryeh makes careful measurements, he begins to make careful cuts.

And because you know you've always wanted to see this, another shot of a PVC pipe being carefully cut.

After careful cutting (which was done after careful measurements, which were taken after calculations were made, chad gadya...) Yoni and Eli sand "smooth" the ends of the pipe.

From left to right: Teflon goop, PVC cement and PVC pipe primer.

The cut, and ready to be glued pieces of the potato projectile device (along with assorted tools).

Yoni primes the pipe...

and glues it together.

Yoni spreads Teflon goop on the threads of the screw fittings.

And the pieces are screwed together at the valve.

Back to Pictures

Completed:

Yoni with the completed potato projectile device in our lovely backyard.

Back to Pictures