This is a relatively simple potato cannon which is a great starting build for an amateur. It can fire a potato about 150 meters when using the correct amount of propellant and fired at 45 degrees.

It doesn't have very efficient chamber to barrel ratio, however this ratio can be changed between firings simply by moving the potato up or down the barrel before adding the propellant. The low efficiency does have an advantage, when fired, a really load bang is produced from the 'un-used' pressure from the combustion - the great feature about combustion cannons!

All piping/plumbing components are made from ABS.

• 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

Note: Method for preparing surfaces that need to be solvent welded are as follows:
Prepare the two surfaces that are to be joined by lightly sanding them to roughen the surfaces and clean with methelated sprits or some other cleaner, then apply the solvent weld generously to one face of the material and then promptly push them together firmly.

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), as shown in the photo left.






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 (refer to photo on right).
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 tubing (which is used on the end of the fabric for blinds) and cut square bits of ABS for sides. Its a bit of a "make it up as you go along" method, but it seems to work just fine! Just look at my photos below...




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.







Lastly, 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! The cannon's finished, here are some more pictures of it:

This is just a small guideline to operating the cannon - to get best results you will need to practice and develop you own methods of operation.



• Unscrew the access plug to allow air to freely pass through the cannon before loading a potato/projectile.
• Take a large potato and firmly press it down on the end of the barrel to cut a potato projectile.
• Using a large dowel push the potato down the barrel.
• Now you add the propellant - spray about a seconds worth of hair spray (or some other propellant) into the combustion chamber. You will need to perfect the correct amounts by trial and error.
• Quickly screw the access plug back on to the chamber.
• Ready aim FIRE!