This was my first potato cannon. It used basic solvent welded plastic pipe fittings from the local hardware store and I didn’t really consider the combustion chamber to barrel ratio in its design. It only took about an hour or so to put the thing together and I was well on my way to getting hooked on building cannons. The following content is from the original project page.
All piping/plumbing components are made of ABS plastic.
- 50mm Ø, 90°, sweeped tee connector
- 50mm Ø, access plug
- 32mm Ø, access plug
- 32mm Ø, double socket
- 32mm Ø, long tail bend
- 32mm Ø, 40mm long pipe
- 50mm Ø, 20mm long pipe
- 50mm Ø, to 32mm Ø, reducer
- 50mm Ø, 750mm long pipe
- Piezoelectric sparker from a lighter
- Sheet of ABS 80mm x 80mm x 2mm
- Two: 25mm lengths of 2mm Ø thick insulated copper wire (mains wire)
- Solvent weld cement
Construction of the cannon
I solvent welded the 50mm Ø, 750mm long pipe; the 50mm Ø, 90°, sweeped tee connector and the 50mm Ø, access plug together to construct the barrel and combustion chamber.
To make the handle I solvent welded the 50mm Ø to 32mm Ø, reducer; the 32mm Ø, 40mm long pipe (female to female connector); the 32mm Ø, long tail bend and the 32mm Ø, double socket (male to male connector).
I cut a segment about 20mm wide in the 50mm Ø, 20mm long pipe as shown in the top right of the photo. This needs to fit inside the reducer and leave enough room to let the two copper wires to fit snugly between the gap. With the sheet of ABS I made a blanking plate by cutting out a 50mm Ø circle. I cut a notch out the side to allow the copper wires to pass through snugly as well (see photo on right). The blanking plate is used to stop the combusting fuel pressure from blowing up in to the handle section when the cannon is fired.
The copper wires were passed through the handle and the blanking plate and ring were then solvent welded into place. The gap between the end of the wires is important for successful ignition of the propellant; set the gap between the two wires to about 5mm and change accordingly when cannon is complete.
This next bit was probably the trickiest. To attach a wire to the metal base of the sparker, I made a ‘cup’ to fit around the end of it, out of thin metal and soldered a wire to this. You must not solder to the base/end of the sparker as this causes it to fail and stop sparking!!
Using the rest of the ABS sheet I cut and made a casing around the sparker. I used a short section of oval plastic tubing and cut square sections of ABS for sides. It was a bit of a ‘make it up as you go along’ method, but it seemed to work just fine!
I then cut a square hole in the access plug to allow the sparker to fit through it; as shown. I solvent welded the sparker holder to the access plug and held it in place for about 5 minutes to allow the weld to set.
I soldered the wires from the sparker to the two copper wires in the handle, and then separately wrapped the exposed parts of the wire with insulting tape.
And that’s it! Here are some more pictures.