Tag Archives: spudgun

Pneumatic Potato Cannon


Originally published: 2002

After building my first combustion cannon I wanted to try a cannon that was slightly different. The pneumatic cannon works on the principal of using compressed air in a sealed chamber to be suddenly released to propel a potato rather than using the combustion of a propellant. This cannon was again build using basic heavy duty plumbing materials and operated up to a pressure of 100psi. The following content is from the original project page.

Materials used

All piping/plumbing components are made from pressure rated ABS – 120psi.

Two 50mm Ø, 90°, bend
50mm Ø, 1200mm long pipe
40mm Ø, 1200mm long pipe
Two 50mm Ø, double socket
50mm Ø, access plug
50mm Ø, 60mm long pipe
Two 50mm Ø to 22mm Ø tundish
Two 22mm Ø, 80mm long pipe
50mm Ø to 40mm Ø reducer
50mm Ø, 190mm long pipe
50mm Ø, 220mm long pipe
22mm Ø, levered ball valve
A car tire valve
50mm Ø, 10mm long pipe (or ring)
50mm x 50mm sheet of 5mm squared wire mesh
Solvent weld cement

Construction of the cannon

I solvent welded the two 50mm Ø, 90°, bends; the 50mm Ø, 1200mm long pipe (chamber pipe); and a tundish together as shown. I then solvent welded a double socket and access plug to the other end of the chamber pipe, also shown in photo. To add the car tire valve to the access plug I simply drilled a tight fitting hole in the centre of the access plug ‘cap’ and inserted the valve.

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I then made the valve fixings. Using a 50mm Ø, 60mm long pipe and the ball valve fittings, as shown in the first picture, I solvent welded the pipe into the tundish and screwed the parts together attaching the ball valve (making sure that the ball valve was in the correct position for firing) using pluming wrench to make sure they were tight. I did this for other tundish to complete the valve section.

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To stop potatoes from getting stuck in the tundish/reducer section, I used some wire mesh and a ring cut from an ABS pipe. I solvent welded the mesh to the inner face of the reducer and then welded the ring inside to hold the mesh securely in place. See photos. The barrel can now be solvent welded into the tundish.

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To make the cannon structurally strong, I made two separator supports to fit between the barrel and the chamber. The support nearest the valve is positioned between the chamber and the tundish attached to the barrel. I did this by cutting the pattern shown in the photo to a short length of pipe, which fit flush with the walls of the tundish/chamber. This was then solvent welded into position. The second support fits flush with the end of the chamber and slots over the barrel (the barrel passes through a hole in the support at 90°). This is then also welded into place.

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Here is the cannon completed – I do like the double-backed design of this cannon!

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Potato Cannon II


Originally published: 2004

This was my second combustion potato cannon. It was a significant improvement in efficiency and size over the first cannon. The following content is from the original project page.

This is my latest combustion cannon, and I have tried to make it as efficient as possible with a 0.8:1 barrel to chamber ratio. It measures 3.65 meters long and weighs quite a lot due to its 6mm thick walls. The power behind this new cannon is a brilliant feeling! It quite happily fires potatoes well out of sight, I just need to remember to remove the length of dowel used to load the potato before firing…it’s not supposed to be a javelin cannon!

The one disadvantage is its size and weight which make it particularly difficult to transport places – I usually get a friend to help and we usually get to deal with the public’s bemused looks on our way to the firing range.

Materials used

All piping/plumbing components are made from PVC.

110mm Ø, 80mm long pipe, 3.2mm thick
110mm Ø, 65mm long pipe, 3.2mm thick
Two 50mm Ø, 3000mm long pipe, 2mm thick
110mm Ø, access plug
Two 110mm Ø, double socket
110mm Ø, to 50mm Ø, reducer
110mm Ø, strap boss
50mm Ø, to 32mm Ø, reducer
32mm Ø, access plug
32mm Ø, double socket
32mm Ø, long tail bend
32mm Ø, 40mm long pipe
50mm Ø, 20mm long pipe
Two 300mm lengths of 2mm thick insulated copper wire
Piezoelectric sparker from a lighter
Sheet of PVC 80mm x 80mm x 2mm
Two: 25mm lengths of 2mm Ø thick insulated copper wire (mains wire)
Solvent weld cement

Construction of the cannon

To make the combustion chamber section, I took the 110mm Ø, 65mm long pipe and marked out a straight line on which I would cut along. This was to produce a sleeve to fit on the outside of the 110mm Ø, 80mm long pipe as the chamber needed to be thicker to withstand the large pressure build-up from the combustions when firing.

Getting the sleeve onto the other pipe was quite tricky – I used pieces of wood to pry the sleeve open. I then applied a small amount of solvent weld to the outside of the other tube and passed the inner pipe through it. I then removed the wood to close the sleeve over the inner pipe, making sure it was in the centre.

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I then cut rings from a length of 110mm Ø pipe; and cut a plate to fit in the 110mm Ø reducer (see photo). This is simply to add strength to the reducer as it needs to be thicker and stronger around the ‘corners’ of the join in the reducer.

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I solvent welded two 110mm Ø double sockets to each end of the combustion chamber section. I then solvent welded the 110mm Ø access plug and 110mm Ø reducer into these double sockets.

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Using a hole saw, I cut a 50mm hole in the front, top of the combustion chamber to allow the igniter to enter the chamber and allow the strap boss to fit snugly when solvent welded to the side (see photo). The position of this whole was to position the handle as close to the centre pivot of the cannon as to compensate for the weight of the 3 meter barrel! This will then make holding the cannon easier.

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This next bit was another tricky bit. The strap boss now doesn’t fit perfectly around the chamber as I have added the sleeve and increased its diameter. I applied solvent weld all round the boss and whole on the chamber, and QUICKLY held it in position with a couple of g-cramps to hold the strap boss flush with the side of the chamber – it was very important that this was a good, strong fixing! I also used a bent screw to fasten the strap boss shut shown in the photo.

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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).

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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.

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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.

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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!

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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.

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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.

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This handle was solvent welded onto the chamber of the cannon, making sure that the ignition wires where positioned correctly within the chamber.

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This is yet another tricky bit, which involves a lot of brute force and a wall! I cut a straight line down one of the 3 meter 50mmØ pipes using a steady bench, clamp and a jig saw to make a sleeve for the barrel. Then I inserted the end of the uncut 3 meter pipe into the sleeve. Using the wall I ‘carefully’ banged the pipe into the sleeve (making sure I didn’t fracture the piping). the sleeve should be short of being flush with the inner pipe to allow the barrel to fit into the reducer (see photo). I also cut the other of the barrel so it was flush. The barrel was then solvent welded into the reducer, with the help of a friend.

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After leaving the cannon’s joints to fully set it was ready to go!

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