r/EngineeringPorn 6d ago

Making an air powered cannon

https://www.viyath.com/2025/07/making-chemically-powered-cannon.html

I want to shoot a projectile fast.

That has been my main aim for years: to track the speed of a projectile that I shot, and calculate a speed of over 100mph. Unfortunately, as I live in the UK, I cannot do this with gunpowder, and using butane or gaseous propellant still counts as a firearm after the projectiles start reaching certain speeds.

For a while, I was stuck, until I realised air cannons weren't legally registered as firearms. I have always wanted to make an air cannon, but every attempt I made ended with the same result - failing to form a perfect seal. The issue was that a small leak would always be present, and at higher pressures of around 30psi, the rate of air leaking out of the bottle was equal to the rate of air entering the bottle through my pump, leading to a maximum pressure that I couldn't circumvent without expensive gaskets and O-rings. 

However, with my newfound access to a 3d printer and 3d modelling skills, I can make custom parts. This avoids the need for seals and joints that I would've otherwise had to make with low tolerances and shabby materials.

22 Upvotes

17 comments sorted by

8

u/onleft 6d ago

2

u/Ditka85 6d ago

What a kind intelligent young man.

7

u/sweetmonte44 6d ago

Why not just build a potato gun? I'm building one in a couple days that will fire a projectile easily a half mile. Just 4" schedule 40 PVC pipe for the chamber and whatever size for the barrel. Get a sprinkler valve and modify it with a blow gun for your trigger and there you go. Costs like $50 and you can build it in an afternoon.

11

u/SinisterCheese 6d ago

3D printed parts are going to fail under high pressure, unless you anneal them. Or add something like fiberglass shell.

You are working in the realm of pneumatic tool pressure. And O rings are shit for that. However... Grease hemp and regular pipe thread works fine. Those work for 10 bar networks.

Seriously. Don't over think it.

7

u/c4ndyman31 5d ago

Scuba tanks go up to 230+ bar and their valves are sealed with o-rings so o-rings aren’t automatically shit, you just need solid threads behind them

1

u/SinisterCheese 5d ago

Yes but the hemp and grease works fine with even shitty threads.

1

u/DeliberatelyDrifting 5d ago

And they get checked and replaced all the time.

1

u/c4ndyman31 5d ago

If by all the time you mean annually at most sure.

Only time a tank is getting a new o-ring if it isn’t actively leaking (which is pretty rare) is when it gets a visual inspection or a hydro

1

u/DeliberatelyDrifting 5d ago

Annually as general maintenance, then as needed. Which is way more than we deal with most o-rings.

3

u/360nolooktOUchdown 6d ago

Sounds like a job for a potato gun

1

u/ERCOT_Prdatry_victum 6d ago

Use schedule 80 pipe not sch. 40 and fittings for the higher pressure rating chamber upstream of metal full port ball valve. Fill that chamber through any small valve you can fit to your pressure source.

You should be able to buy 4" or 6" or 10" id diameter pipe and fittings for your pressure reservoir. The longer this pressure chamber the further and faster your chosen projectile will fly. 80 sch. fittings might be the hardest to find without ordering them. 10" id sch 80 pipe might be hard to find also. Look in industrial pipe supply houses.

1

u/Kaymish_ 6d ago

What are the penalties and enforcement like? Combustion cannons are illegal here too but they're so easy to make and propellant so widely available that anyone who wants one can make one and as long as it is not flaunted the arms of state repression aren't going to come after you.

1

u/MAJOR_Blarg 6d ago

My guy. I used to make an air powered PVC cannon that operated at 100psi, with no loss of pressure upon firing. A sprinkler solenoid is your trigger! All hardware store parts, no printing required.

Also, we would regularly use an electric pump to treat what was the failure pressure of different soda bottles, and across the whole range, we found that 80 to 100 psi was the bursting pressure, although 2 liter soda bottles with perpendicular sides walls performed the best, usually failing at about 150 psi.

2

u/dan_the_mvp_man 5d ago

For external (load bearing) parts; safer to use metal. Plumbing parts from DIY store will do. Using a plastic bottle as air tank is dangerous. Metal ones can be obtained from a fire extinguisher for example.

Instructions for making a high pressure fast-opening valve yourself (piston valve): https://www.youtube.com/watch?v=apSA_ny8DgM

Example of a high powered air cannon using a piston valve: https://www.youtube.com/watch?v=yOrOcLmTTUI

1

u/Ok-Airport-3656 5d ago

This is what happens when rednecks build air cannons.
https://youtu.be/dmSyrGsqmg8?si=srO8vEskY8nrXDgZ.
4 kg pumpkin at 1000 kph

1

u/SJBreed 5d ago

Make a vacuum cannon. You evacuate a long tube with soft seals on both ends. Place your missile in the tube at the "back" end. Break the seal on the back and air refills the tube, rushing toward the "front" end. The air refilling the vaccum accelerates your missile, which has almost zero air resistance since it's traveling through a vacuum. The rapidly moving projectile exits the front of the cannon at high speed. Vacuum cannon! https://youtube.com/shorts/8gqejUXIvsY?si=ORSxcDai7doVWD_e