Tag Archives: combustion

Mini Cannon

Introduction

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.

Materials used

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.

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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.

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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).

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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.

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And that’s it – a pocket mini combustion cannon that you can take anywhere!

Potato Cannon II

Introduction

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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Potato Cannon I

Introduction

Originally published: 2001

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.

Materials used

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.

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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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And that’s it! Here are some more pictures.

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