Spud Mark I

This is the first Spud gun that I have build. Building the gun was quite easy, debugging it cost a lot of time though. The first time I fired the spud gun, my first spud gun ever, I was surprised, pleasantly surprised.

After constructing the gun and waiting a day for the glue to dry I went into my backyard equipped with a can of hairspray, a big potato and of course the spud gun. Just while I was preparing the gun, one of my neighbors walked into my backyard. His first reaction: what the #@! is that? Well, that’s what is called a “potato cannon”. My curious neighbor staid, as usual, to witness the first test results.

First we put a potato in the barrel, then I filled the combustion chamber with a small burst of hairspray, screwed the cap back on, aimed the gun toward the sky...... and pulled the trigger...

WOW

... Did you see that....? Both I and my neighbor saw the first potato fly over a few blocks of houses. Astonished by the power of the gun we kept track of the potato until we saw the potato go down and we lost sight of it due to the housing in our neighborhood. After we lost sight of it the potato could have hit anything or anybody, we just hope it did not cause any damage, or worse hurt someone. It became clear to us that we where going to have loads of fun shooting potatoes. It also seemed like a good idea to move our activities to a less populated area.

A 5 minute drive brings us to a construction site were a road is being build. Here we can fire at will, nobody was there at the time, it was a beautiful quiet Sunday afternoon.

In the meanwhile my father in law also accompanied us. The three of us prepared the gun, aimed and fired. Again a wow moment and lost of laughter... Lets try again, preparing the gun, aiming and firing..... firing.... firing.... #@! ..... nothing happened. The potato was still in the barrel and was definitely not impressed by our firing attempts. About 20 minutes and a lot of debugging efforts later we had another go. This time firing the gun resulted again in a beautiful wow moment. Ok, let’s try again, after preparing the gun we fired and uuh fired.... and fired... again no result. We put the gun aside and in the meanwhile we launched several water rockets. About 30 minutes later my father in law picked up the gun, aimed and fired away..... BANG... and another potato tried to leave the planet. Click here to see my father in law firing the gun... watch his reaction... (672kB Movie).

About a week, a few kilos of potatoes and lots of hairspray later I figured out what was wrong. To test my hypothesis I fired the gun, blew fresh air into it, removing all left over gasses from the previous combustion. Prepped the gun and fired... YYYEEESSS! My hypothesis seems right. So, what happened was that there was not enough air in the combustion chamber to burn up the hairspray. After filling the chamber with air and then spraying hairspray into the chamber we get a good mixture of flammable gases which ignite when exposed to a small spark. In short the key to success is proper ventilation of the combustion chamber. What we do now is ventilate the combustion chamber after firing. I can assure you that this works, and causes a lot of pain in the muscles we use for laughing.
 

_{Click the images for a close-up.}