Potato Cannon - V3

This is the best cannon I've come up with to date. Receiving some inspirado during a trip to the hardware store, this design was conceived on the spot, assembled and tested in about 3hrs. It takes the versatility of interchangeable barrels and adds an ergonomic design to the chamber. It also gets a better punch and takes less saw work to assemble.

finished chamber
A nice patriotic backdrop for the cannon.

finished chamber 2

Here's a materials list:

Part Qty
 2" PVC Pipe ~5" 
 4" PVC Pipe ~2" 
 2" Female Cleanout Adapter
 4" Female Cleanout Adapter
 4"x2" Flush Adapter
 4" End Plug
 2" End Cap
 2" Male Adapter
 4"x4"x2" Y-Adapter
 4"x4"x2" T-Adapter
 Grill Ignitor
 PVC Cement
 PVC Primer
 Hot glue A few sticks 

As you can see, this cannon is not too much more difficult to construct than the previous model. In fact, it is in a few ways easier. The chamber is made of two primary pieces, the 4-2 inch y-adapter sections. The one towards the end is a 45degree y-splitter. The one on top is a 4X4X2 T-adapter (I don't remember the exact names from the hardware store, you'll know them when you see them.) These pieces are cemented together. Do some dry fitting before hand to get a comfortable angle for the handles. Notice that the handle with the ignitor points straight up when in use, and the handle on the side points downward slightly. This is the best angle we came up with. To find a good angle for you, put your right hand out in front of you as if you were holding the trigger assembly. Put your left hand out in front and act as if you were holding the handle. Figure out how your hand naturally rests when extended out and which angle is the most comfortable. When you figure out the angles, cement the two pieces together.

Next cement in the 4 inch female adapter into the end of the chamber and the 4-2 inch flush adapter into the top. Cement a 2 inch female adapter into the 4-2 inch flush adapter. When that is complete, cut to length a piece of 2 inch pipe to be used for the handle (the exact length is not important, just make it a comfortable size for your hand.) Then cement that into place and cement a 2 inch end cap on the end.

To make the igniter assembly (sorry there are not detail pictures of it, I may get some cross-sectional drawings up eventually) You need to get a 2 inch end cap and a 2 inch male adapter. Drill a hole in the end cap to fit the ignitor as you would for the previous cannons. You need to do a little bit of jury-rigging on the ignitor. Get a couple of long wires and solder them onto the two wires coming from the ignitor. This will allow the sparker to reach into the chamber. Next, place the rigged ignitor assembly through the hole in the endcap. Hot glue it into place. This will be a little tricky, all you have to do is start squirting the hot glue down towards the hole. You don't have to get close to the hole, just be very liberal with your hot glue use, the more you use now, the less you'll have to use later if it comes loose. After the igniter is glued into place and the glue has cooled, you may cement on the 2 inch male adapter. Now you need to fix the end of the wires from the ignitor so that they stay apart so a spark may jump between. I used a cable staple to accomplish this. A cable staple is essentially a piece of plastic with two nails in it on opposite sides. I soldered the two wires to the two nails, then bent the nails so they were close enough to spark. After that, I hotglued it all in place so the nails wouldn't change position. After this, on the 45 degree y-adapter piece, cement on the 2 inch female adapter to the end, allowing a port to accept the igniter assembly. You can now feed the wires through the hole and screw the assembly into place.

inside the chamber

The wires should now hang down into the chamber. To prevent it from rattling around tape it down inside the chamber.

attaching a barrel

You can use the same barrels that you used for the previous model. They are all interchangeable because we're using a 2 inch standard. Load the cannon the same way. Put a potato or other ammunition into the barrel. Then screw the barrel into place.

fueling the cannon

Fuel this cannon the same way as the previous model as well. Load the fuel in through the end, screw the cap on, then...

aiming with a large barrel

... take aim and fire.

comparison with version 2

Here's a comparison shot with both the model version 2 and 3. You can see how version 3 is superior.

WARNINGS

When using hairspray as a propelent avoid spraying it directly on the threads of the screws. The screws will stick together and may cause the barrel to break if you force it too much. If your barrel does get stuck DO NOT force it, instead you can use channel locks or a pipe grip which may be bought at a hardware store. These tools will give you much better leverage and will unscrew them with minimal force. Trust me, I learned from experience. You should also wash out your cannon when you're done, gunk tends to build up in it.