Air Powered Potato Cannon

I had to build a potato canon for a science project and needed one where I could get a consistent launch force. The typical hairspray cannon would not be appropriate for this purpose so I constructed this air powered launcher as a modified version of Pnewton's Petard from the excellent book "Backyard Ballistics". Typical results were a range of over 300ft using a weight, nonsealing projectile, I am sure a potato would go much farther.

Step 1: Materials

The materials needed for constructing the air cannon are as follows:

·shaping file
·22-inch length of 1½-inch diameter schedule-40 PVC pipe
·1.5-inch diameter male-threaded PVC pipe adapter
·PVC primer
·PVC cement
·Teflon pipe tape
·1½-inch diameter female-threaded PVC pipe adapter
·1½-inch diameter to 3/4-inch threaded PVC reducing bushing
·Electric drill with various sized drill bits
·1 rubber-coated, narrow-diameter, replacement-tire air valve
·2 3-inch-diameter PVC end caps
·Wrench
·2 9-inch-long pieces of 3-inch diameter Schedule-40 PVC pipe
·3-inch x 3-inch x 1½-inch PVC tee connector
·3/4-inch diameter short iron pipe nipple
·3/4-inch ball valve (It has also been suggested that a pneumatically modded sprinkler valve would allow for a faster and there for more powerful launch. I have no experience with this so for the sake of this article we will use the ball valve.)
·3-foot length of 1-inch diameter wooden dowel or broom handle
·Foot-stabilized air pump

Below is the diagram and the assembled materials.

SAFETY NOTE: I have received several comments regarding the use of Cellular Extruded Piping. In short - don't use it. It is not meant to deal with air pressure and could explode violently producing hundreds of deadly shards. I have not had this occur yet but if at all possible please use a better piping.

Step 2: Construction

The construction of the launch apparatus (see below for a diagram) is as follows.
Attach 22-inch-long pipe to the 1½-inch male pipe thread adapter using PVC cement.
Attach 1½-inch female adapter to 1½-inch to 3/4-inch reducing bushing using PVC cement and allow to cure.
Screw male pipe thread adapter assembly to female pipe thread adapter assembly carefully.
Drill hole in one 3-inch end cap the diameter of the tire valve. Insert the tire valve into the cap.
Attach both 3-inch end caps to 3-inch diameter pipe with PVC cement.
Use solvent weld to attach the 3-inch pipes to the tee connector.
Take the second reducing bushing and attach the 1½-inch opening to the tee connector with PVC cement.
Wrap the heads of the 3/4-inc pipe nipples using Teflon pipe tape.
Insert the nipples into the ball valve (or as it has been suggested the pneumatically modded sprinkler valve).
Screw the ball valve-pipe nipple into the 22-inch barrel.
Screw the new barrel assembly into the pressure chamber.
Allow to cure overnight.
Wrap the pressure reservoir with three layers of duct tape. (optional)

Step 3: Safety

To test the safety of and seal of the air chamber additional steps must be taken. Close the launch valve and pump the reservoir up to 10 PSI. Sprinkle soapy water on the joints. If bubbles appear, joints are not airtight and you must restart. If no leaks are found, repeat safety step 2 with 30 PSI. When done, aim the barrel in a safe direction and release the pressure.

Step 4: Firing!

The actual act of firing the cannon requires further knowledge. Use extreme caution in aiming device. Make sure all parts are securely attached. Check launch platform after every launch for signs of wear. DO NOT over pressurize the pressure chamber. 30 PSI should be used as a high average. Use ear protection and eyewear. Clear the area in front of cannon for 200 yards. Clear area around cannon for 25 yards.

Projectiles:
I used a weighted ping-pong (filled with clay) for my experiment with tissues as wadding. I needed this to have a consistently sized and weighted projectile. I encourage the use of potatoes however as when you jam one down the barrel, they lock it up and nice airtight. That means you get way more range. Moreover, who doesn't like shooting potatoes?
DO NOT shoot pointed, explosive, fragile, or living projectiles. I am not responsible for any of the damage you may incur in such a case.

Remember:
An angle of 45 degrees should give you the greatest distance. This cannon shoots very accurately and I can consistently land my projectiles within five feet of each other.
See how close you can land to a target and assign points to see who is the best bombardier.
This cannon is tons of fun but can also be very dangerous, remember to use your head and think about what you're doing. I'm not responsible if you put a potato through someone's head...

Have fun!

Comments

[Private_Anguish]

this is cool

[PlasmaGuy101]

if you use smaller diameter pipe for the chamber then you can really push the pressure, i have a 1" chamber and can pressurize it to 200 psi .

[Qwerkwerx]

COOL!

[Luziviech]

well then, why don't you wrap your air chamber into a metal "chamber" - just use pipes that got a bigger inner diameter than the outer diameter of your plastic chamber and fill batting into the interspace to cushion the eventual outburst? (Just an idea)

[marshallcan]

Is there a way to build this in such a way to have multiple pipes shoot at the same time? Also, is there a way to build this so that the pipes are built to "shoot" at a precise time, like to music? Thank you.

[KevinF51]

I blieve there is a way. all you have to do is get like 4 t cuplings and 2 elbows. All you have to do is where the barrel is just add 1 t cupling and then exstend off that and then add as many barrels as you want.

[DaveyH]

I remember building one of these for a contest. How I set it up though I was able to hold it and shoot it off my shoulder. We want to get a "bazooka" effect and it worked out pretty well. There was quick a backlash from the kick, but that sucker launched.

http://www.dewcopumps.com/Home/Manufacturer/Flojet

[nutsandbolts_64]

I still remember when I made my first one. The valve was so tight it took me 1 second to fully open it, therefore, much energy was wasted. The valve used must be airtight and smooth-opening for efficient operation. The faster the valve opens, more air can and will come out in a given amount of time. Just a reminder. And please do use ABS piping, it's safer due to its reaction to a catastrophic failure (i.e. it turns into strips and not bits and pieces similar but not exactly like a grenade, plus PVC will be hard to show up on x-ray)

[ilpug]

Ok, let me clarify something: Combustion powered guns are better built with ABS for the reason you suggested, because the action of a combustion cannon results in an almost instant shock pressurization of the system (I.E, goes boom). ABS is better suited to quick shocks or bumps, so it is superior for combustion cannons.

ABS cannot be used for air cannons though, because it simply cannot hold the pressure. PVC is designed to hold pressures up to 500PSI+, depending on the pipe diameter. The trick is to keep the pressurized air chamber in a safe spot, or pad it against bumps. ABS can, and will, explode if you try to pressurize it.

Pnewtons Petards like this one are pretty safe as far as air cannons go.

[jmlazer]

So far, ABS has worked fine for me under pressure.

[ilpug]

until it doesn't...

[nutsandbolts_64]

The trouble is that 2 years ago, most of the PVC I used wasn't pressure-rated, add to that we didn't even have ABS piping. The thing is PVC is designed to withstand water pressure. Air is a completely different fluid to work with.

Someone should seriously get a blast shield and attempt to blow up PVC and ABS pipes rated for the same pressure. That should settle the argument.

[ilpug]

I might do that at some point. Make two air chambers of equal volume, pressurize to the same pressure, and shoot them with something.

[ilpug]

I might do that at some point. Make two air chambers of equal volume, pressurize to the same pressure, and shoot them with something.

[soggymushrooms]

Hard to show up on x- ray... Way to stop people from building it

[T(M)^2]

Privyet, comrades.

The question I have for you today is as follows: I am looking to build an air cannon with a 6.35mm(or 2.5in., for all of you ingloskiis who still use the English system) bore air cannon capable of launching a .5kg.(1.1023lbs.) projectile 200ft. at a 45° angle. For whoever wants to do the math, what modifications should I make to the specifications above?

Sincerely,
ДЖ

[de0509]

Not really doing much calculations, none actually, but because you are using a quite heavy projectile, you really need a lot of force. and your caliber is big. you need the ball valve to be big as well so as to not give much resistance for the air to flow. maybe try using a big ball valve or any other valves that release pressure fast. maybe 1 inch ball valve instead of 3/4. or maybe if you can use a tee so that 2 ball valves open together. that way, you have a 1.5 inch ball valve from combining 2x0.75 inch ball valve. just make sure they open at the same time. i.e. joining the two ball valve handles together maybe?
depends on the pressure you intend to use. if low, id suggest making the chamber part longer. if high pressure, i think the original should be ok. but that is to be just enough, you may want more power right? maybe double the chamber? keep note that this also increase pumping time.

[T(M)^2]

many thanks, de0509. I shall keep your advice on my mind and in my project.
dasvaydanya.

[sjoobbani]

This works pretty well with fire extinguisher cylinders as a pressure vessel too!

[TygrFr3d]

30 PSI as a high average? If you are worried about it bursting, don't worry. I have taken a 3" chamber to 120 with no issues. And if you want good groupings, maybe have the ball valve open with a tension spring and a catch, so it will open fast, and at a consistent speed.