Intro: Fuel/Air Hybrid Potato Gun
This is for seasoned cannon builders only, as it is complicated for me, a proud builder of over 10. This cannon uses gas or air, whichever is handy, but NOT AT THE SAME TIME. That is a recipe for disaster. This is not an exact plan for one, but the instructions to build one. The dimensions are up to you. It will take a weekend to properly build, and around $40-80 dollars, depending on how expensive your hardware store is. I have a friend with a parent owning an irrigation company, so I didn't have to skimp on anything.
I am not liable for any problems whatsoever occuring while either firing, building, or transporting this machine. It is strictly for fun, and nothing else. Aiming or shooting at anything valuable (Yes rednecks, that includes animals and people) is not a good idea. Thanks!. This design requires some valves to be open and some to be closed at different times. If you get confused, you may have just built a pipe bomb. Careful Please!!!!
Step 1: Parts List
These are the dimensions that I used, but they can be changed to whatever specifications you desire.
2 3+ feet sections of 3 inch diameter schedule 50 PVC pipe. Any thickness will do, I just prefer something a little stronger.
1 3x3x2 connector, with the 2 inch port facing up.
1 4 foot section of 2 inch PVC
1 1.5 foot section of 2 inch PVC
1 Can of PVC primer
1 Can of PVC glue
3 1 inch female threaded ball valves.
8 1 inch male threaded PVC couplings. (2 extra, in case of stripping)
4 3-1 inch PVC bushings.
2 2-1 inch PVC bushings.
Anything else you find in the PVC aisle that could be of use.
1 3 inch diameter end cap
1 PSI gage (optional)
1 3 inch end cap with threads and cap
1 Barbeque Sparker
1 Bike Tire Valve (Schraeder)
Make sure to securely glue and loctite tape and glue every joint possible very heavily. It is a little unsightly, but it wil save you lots of time patching leaks and going to the emergency room.
Step 2: First Steps
Start assembling each section of the cannon. First, the air chamber. This is what it will look like.
If you've built one before, you should know how.
Take your 3+ feet of 3 inch pipe, and drill a hole, about 4-5 inches away from the end.
Place a shrader valve in this hole. Glue it securely. Look to other instructables if you don't know how.
Apply primer and glue, and cap the pipe. It should only have one end open. The PSI gauge is my personal touch, so don't worry about it.
Take one 3-1 inch bushing, a 1 inch coupling, and one of those 3 inch plumbing parts I don't know the name of, but it fits around the pipe. Assemble them, and glue them onto the other end of the pipe. DO NOT GLUE THE COUPLING!
Your Air Chamber, is pretty much finished. I like to be able to disassemble the cannon, so I don't glue the 3 sections of the cannon together. Loctite tape will make this whole thing airtight, but it it is only needed on the couplings.
In the photograph there is a valve, put one on CAREFULLY, as the couplings do strip easily. Make sure to wait 24 hours before putting ANY pressure through it.
YOU FINISHED 1/3 of the project!
Step 3: Assemble Gas Tank
This is much simpler.
Take a 3 foot section of pipe, and put the same kind of assembly as you did on the air cannon, on the end that will enter a valve. Glue it.
Drill a hole about 10 inches away from the end facing away from the cannon. It will need to be big enough to house the sparker part of your BBQ sparker, about half an inch wide.
Prime and glue the female end of your screw on end of the PVC.
I assume you know how to install a BBQ sparker.
Attach another ball valve, with coupling on other end, and you're done with the gas chamber.
It should look like this.
Step 4: The Barrel
The simplest part of the cannon is the barrel.
Simply build another one of the assemblies you have used before, but this time, with a 2-1 inch bushing. Build it, and shove/glue it on to the end of the barrel, and screw on a coupling.
Barrel is DONE.
Step 5: Sorry, Time for the Hardest Step.
This is the body of the cannon.
Take 2 3-1 bushings, and glue them into the tri-hole piece. then loctite tape the couplings to the bushings.
Then, take your 1.5 ft section of 2" pipe, and glue it in.
Build yet another assembly for 2" pipe, and glue it on.
Tape a coupling, and put it into the assembly.
Screw on a valve!
Step 6: Assemble All of Your Parts.
Now, all you gotta do, is screw all 3 sections together, and make sure they line up. It is tedious, but worth it. It will look like this beast.
Precautions to take before firing.
Wait at least 24 hours to put any pressure in it.
Pump up to the maximum rating of YOUR pipe, not mine. I pump to about 200 PSI.
Whatever I have in there, will go so high I can't see it for a good 20 seconds,and extremely far. Too far for me to see at least.
Watch out for stray heads you could whack while transporting it.
A cool tip is, you can build many
HAVE FUN!!! Post pics of the ones that you have built!