Originally published: 2003
I had some parts lying around my bench and I had an idea for a mini combustion cannon. I had a plastic tube that fit plastic BB’s perfectly and a nicely sized pot for the combustion chamber that fits the hand nicely. This cannon works brilliantly with standard BB’s or even potatoes or cotton buds. I did lean very quickly to wear goggles as the projectiles do have a tendency to bounce around the room like crazy. The following content is from the original project page.
Tablet pot/container (e.g. calcium carbonate or vitamin tablets pot)
Piezoelectric sparker from a lighter
7mm Ø (5mm int. Ø), 220mm long pipe
Two pins/thin needles
Two rings of 22mm Ø pipe
A few lengths of insulated wire
Solvent weld cement or multi-purpose adhesive
Construction of the cannon
To attach a wire to the metal base of the sparker, I made a ‘cup’ to fit to its end (see photo). I made the ‘cup’ out of thin metal and soldered a wire to this as you must not solder to the base/end of the sparker as the heat from the soldering iron causes it to fail and stop sparking!! The wires leading from the sparker should be approximately the same length of the tablet pot plus about 50-100mm.
I then drilled a 7mm Ø hole in the base of the tablet pot to allow the barrel to fit through. I also passed the two wires leading from the igniter through this hole as shown in the photo.
To the end of the barrel that is going to be inside of the tablet pot add a very small amount of multi-purpose adhesive to the inside of the barrel – to narrow the internal diameter to stop the projectile from falling all the way through.
The barrel should intrude about 80% of the tablet pot to keep the barrel length long but not have all of it protruding outside to keep the cannon’s overall size down. I secured the barrel to the inside of the tablet pot with some multi-purpose adhesive.
To make the ignition mounting I used a couple of spilt rings of piping cut from a length of 22mm Ø pipe, and fitted one around the other until it fitted snugly in the tablet pot.
I then pushed two pins through the side of this mounting and cut the protruding excess parts of the pins (to make it flush when inserted into tablet pot) to create a ‘sparking bridge’. I then soldered the two ends of the wires leading from the sparker to each pin (see photos).
I then taped the sparker to the side of the tablet pot near where the barrel protrudes from the combustion chamber and also taped a ‘stop’ made from layers of cardboard behind the sparker to stop the sparker from moving when it was pressed. After the sparker was fairly secure I wrapped a final layer of duck tape around it, just to hold it permanently in place.
And that’s it – a pocket mini combustion cannon that you can take anywhere!