there are two types of potato cannons. combustion and air.

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also, these things can kill you

Step 1: COMBUSTION CANNON

The first type the combustion cannon.
it uses a gas, an ignition source, and a compressed area to launch projectiles

Step 2: THE KEY PARTS

there are three main parts to the combustion cannon
1. the compression chamber
2. the barrel
3. the ignition source

for the chamber, you have to put a screw off cap at one end, and a reducer at the other. you need the cap to be removable so that you can fill the cannon. you need the reducer to give the cannon more power, because a 1:1 ratio will not give you the needed power. i also chose to add a male screw adapter, so that i could have different barrels, also if the barrel clogs, you can get it out.

the barrels is a simple pvc pipe attached to the combustion chamber, that you can load from the front, or the rear, depending if you have a removable barrel which i highly recommend.

the ignition source can be almost anything. i recommend a grill ignitor since they are made to produce a spark. you should attach high gauge wires to the metal tabs on the side and bottom, instead of using the supplied wire, the wire given is not too good for making the spark needed, also it is a pain to cut. also, you should solder the end with tin, to protect it from erosion. one last thing, make sure that the ignitor and chamber are one, because is there is a leak, then the gas will come out and hit you. not fun. i just used some marine goop, to seal off the end of mine, just enough to keep gas from coming out.

Step 3: AIR CANNON

the next type is the air cannon

Step 4: THE KEY PARTS

again, an air cannon has three main parts
1. compression chamber
2. barrel
3. release mekanism

the compression chamber MUST be air tight. is it is not your cannon will leak and it is hard if not impossible to fix. i double glued everything and even added a nice coat of epoxy on the inside and out to make it perfect. it once help 60 psi for 2 hrs!

again, barrel is a pvc pipe attached to the chamber in some way, i recommend a removable barrel.

this is where i got creative. you can use a standard ball valve as a release, but it was slow and lost a lot of power, so i decided to go electronic. i used a sprinkler valve, and instead of cutting it open, drilling, glueing, and carefully assembling a blow gun trigger into it, i just put a battery bank on top, added a switch, hocked up to the solenoid, added a box to keep it neat, and had a lightning fast trigger.

WARNING!!! the electric trigger method has more power, but also is extremely load. mainly because i have a 5:1 compression ratio( i now know that that is not good, and am working on a 2:1 cannon) which makes it very load. so load that my neighbors said that if i shoot it one more time they will call the police since it vibrates there entire house( believe me it is that damn load!!)
so i recommend either a ball valve or a 2:1 ratio for the sprinkler valve to barrel ratio.

Step 5: FINAL REVIEW

combustion

pros
decent power
quiet
easy to fire

cons
a little short on power
can be dangerous is back blast hits you

air

pros
has varying power depending on how much air you give it
can have a lot of power
can shoot almost anything

cons
can be very load
takes long to load
harder to build

OVERALL
i say that both cannons are equal.
If you live in a highly populated area or in an apartment, i say don't make one
if you live in a narea with a large back yard, but have neighbors, i say combustion
in you live in an area with a large back yard and few to no neighbors within 30 ft of your house, i say go for air

either way, they both are fun to use

again, these are not toys and can kill you if not used in a proper manner

Step 6: SILENCER

i made a silencer for my cannons. I forgot to take pictures, but type silencer in the search box and you can find the instructions for how to make one.