Instructables
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.
 
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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.
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-CCCP-2 months ago

Pretty nice pipe bomb.

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)
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 ilpug1 year ago
So far, ABS has worked fine for me under pressure.
ilpug jmlazer1 year ago
until it doesn't...
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.
I might do that at some point. Make two air chambers of equal volume, pressurize to the same pressure, and shoot them with something.
I might do that at some point. Make two air chambers of equal volume, pressurize to the same pressure, and shoot them with something.
Hard to show up on x- ray... Way to stop people from building it
T(M)^22 years ago
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 T(M)^22 years ago
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 de05092 years ago
many thanks, de0509. I shall keep your advice on my mind and in my project.
dasvaydanya.
sjoobbani2 years ago
This works pretty well with fire extinguisher cylinders as a pressure vessel too!
TygrFr3d2 years ago
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.
Turtlepwr2 years ago
The fire and danger is half the fun
sci6 years ago
How much safer would it be if you use schedule 40 PVC? what would be a safe air pressure?
ilpug sci2 years ago
If you used schedule 40 for all the parts, and assembled them correctly, a safe pressure would be about 80 PSI. That said, you can go much higher. A good rule of thumb is to take the pressure rating of the weakest pipe in the system (usually printed on the side) and divide that by 2 to get your maximium pressure
waycoobeens7 years ago
Where can you find that tire valve...honestly thats the only part i cannot find...the rest i just got from home depot
Old bike tires.
I actually found a gauge and tire valve in one i use at a plumbing supply house
at advanced auto or other autoparts store.
a tire seriously, I got an old tire and ripped it out
I got mine at Ace hardware.(basically Ben Franklins)
A friend and I decided to build one of slightly different design, which also required a tire valve. We obtained ours by cannibalizing and old, broken BMX bike's front tire.
Hermes (author)  waycoobeens7 years ago
Try a car place like pep boy's. Also, you may want to check the lawn mower section at Home Depot as they may have some valves. ~Hermes
how much does this cost on average? also wat would i need to do to make the barrel bigger, would i have to chance anthing else besides the size of the barrel? also if i use this thing with about 15 psi could i hold it whiile i fire it?
by bigger i mean diameter
Technically, you could hold this while you fired it at 100+ PSI. The design of these guns is such that it makes firing while holding a bit awkward.
tulavatalo4 years ago
will this work with bigger pipe and bigger valve?
 Maybe. You'd need a bigger Air Chamber though. I'd suggest bigger than the scale your increasing it at (ie, if you double the barrel diameter, 2.5x the Air Chamber.)
ilpug Lance Mt.2 years ago
Note that with bigger pipe, the pressure rating decreases.
LX_COCOS7 years ago
nice job but ive asked my dad for permission to do this but he says it could blow up in my face is this safe? if so how can i prove it to him any help apreciated
Hermes (author)  LX_COCOS7 years ago
If you use pressure rated pipe (generally about 150 PSI) and accurately glue your joints, this is a very safe design, far safer than the hairspray cannons. The recommended max of 30PSI that I have included is a fifth of what the cannon can take ensuring that it is very safe. As long as you follow the instructions, use pressure rated pipe, glue well, and don't over pressurize, this is far safer than a conventional lawnmower... ~Hermes
30PSI??? REALLY IS THAT SAFETY PRECAUTION REALLY NECESSARY?? MY 1ST PETARD IS PVC AND MY SECOND IS STEEL. THE PVC GOES UP TO 145 PSI AND STEEL 450. MAKE A STEEL CANNON. PLUS USE A COMPRESSOR.
I would be very scared to use a cannon at 145 PSI.
Hey there...I'm pretty new here, heh. However, I'm planning on building a potato gun this year for my science project. I couldn't come up with anything, however, one of my close friends suggested a potato gun. Consider me stupid, because I think I am many times, however...wot does a potato gun have to do with science? Am not a science person at all. Matter of fact, 'tis the subject I hate viciously. And I was going through a few sites, came accross this one and noticed that you knew wot you were talkin' about. I need some help. Am desperate, I'd say. Science fair is on May 14th, I'm sure I'd get it done before that, but I need all the help I can get... I've settled down to doing a potato gun as my science fair project. If you can help me, then talk with me here...But, I'm a new comer, and I'm very ignorant of technology and this...er..site(?)/chatplace thinger...Ahem. So, I'd not know how/when to sign online. If you can help, I'd be much too thankful and you may email me at kharosh@hotmail.com Your help would be very much appreciated and some weight off my shoulders. :sigh: - Kharosh
 2 years late, but nevertheless... -- Physics entails the study of motion, force, gravity, etc. A "potato gun" is a less formal way of saying a "Projectile Launcher". In physics, you study a topic specifically named Projectile Motion. See the correlation? Air pressure is built up (in this model), and you're monitoring the various forces exerted on the object leaving the barrel.

Cheers.
Tell your dad that the teapot in the kitchen could also blow up, the oven could explode, and etc. Nothing will happen to you if you don't set yourself up for it. Example? Looking down the barrel, even when its not pressurized, is stupid. I said the same thing to my mother, back when I made my first combustion (...explosion...) launcher, and she let me do it. I've switched over to pneumatic due to school regulations.

Cheers.
im going to quote you on that first line. somehow somewhere someday ill quote you
owwio LX_COCOS4 years ago
i have fired something alot like this at 120 psi with no problems.
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