The Yeet Machine

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
headslammer
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Tue Jan 26, 2021 4:23 pm

Hey everyone!
Been lurking here for a while after discovering this place while doing research on a pneumatic cannon, finding solutions to problems, etc. Now that it's been designed, built, and tested a few times I figured I should post here.
I'm going to break this down into parts/chapters to make it easier to digest or if you just want to skip to the bottom to see videos of fruits exploding.

Chapter 1: The Idea

After making a very underwhelming metered propane cannon that only worked about ~50% of the time (very nerve-wracking btw), I decided to look for better options. I quickly found this place, and after taking one look at the hybrid section, I decided to build a pneumatic cannon.

I’ve always loved tanks and tank combat, so I decided to attempt to make it look like an anti-tank gun, meaning I’d also need to make a mount of some sort.
Therefore, I set some main objectives for this build:
  1. The barrel will be at least as tall as me, and 2” in diameter
  2. It will be fully breech-loading, no disconnecting barrels or other nonsense
  3. It should be able to easily be placed into a mount for the cannon that can elevate, traverse, and is easily transported (at the time, my biggest car was a two-door VW GTi so space was at a premium)
  4. It will be bigger and more powerful than my last design (not hard)
Deciding on an over/under design and armed with just an idea of what I wanted it to look like in my head, I set out to find parts to fit that idea. Rather quickly, I realized that the valve was going to be an issue. Despite having no actual knowledge on this topic, I had a gut feeling that the PVC ball valves I was looking at were just too slow to be effective at this scale. Deciding to do some research, it was around this time I found websites like spudtech, advancedspuds, and finally this place. With a breadth of new-found knowledge at my disposal, I got to work and spent a few days researching valves.

Chapter 2: The Valve

Despite not being 100% confident in my understanding of them, but being somewhat confident in my ability to build one, I decided to build a chamber sealing piston valve. Taking elements of the supah valve, designs from multiple other websites, and numerous threads here, I came up with my first design.

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Nothing too special here, just a piston made out of a bolt, washers, plywood, etc.
However, as I started finding the materials to make this, I started to have doubts about the integrity of it and if it would seal. Again, I didn’t really understand this, like where the air goes, how it gets to the chamber, etc, so I went back to the drawing board.
Here's what I came up with:

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Having discovered solid PVC rods on McMaster and coming up with the above design, I got a friend with a lathe to turn the grooves for the o-rings and drill the hole in the center for the check valve. Feeling good about my design, I spent the next 3 days building, fitting, and buying parts. Finally, it was finished.

I started to fill it with my tire inflator (didn’t have a compressor, I was gonna shoot this at my friend's place anyway), and oh boy did it leak. It really leaked.
I spent the next week working dusk till dawn sweating my ass off in my garage trying to get it to work before I left for a cross-country trip so I could have some closure. Alas, the highest it would hold was 30psi.

Then, while looking through threads on this forum somewhere in Montana, I found a thread where someone was talking about industrial dust collector valves. Did some digging, found a site that sold them, and ordered a 2” Goyen Pulse Valve. Two days after returning from the trip, the cannon was complete.

Chapter 3: The Mount

Having already spent so much time on this project, I simplified my ideas for a mount, deciding not to bother with the traverse mechanism. After spending a couple of days building and troubleshooting, here's what I came up with:

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The cannon itself is clamped to the mount by the two wide vertical planks at the front and back of the mount. The rear legs can be removed to save space, and the elevation mechanism is a long threaded rod run through a nut near the chamber.

Chapter 4: The Ammunition

Remember how I said I like tanks and tank combat? Well, admittedly this thing wasn't designed to shoot potatoes. Rather, it's primary ammunition would be these:

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Heavily inspired by modern APFSDS rounds, I found 12” long nails and crudely affixed sheet metal fins to the rear using a piece of PVC and epoxy. I used that pink solid foam insulation to make a sabot for them and also for wadding behind it.

Along with these, the main things I shot were potatoes, tangerines, sections of 2” wooden dowel, and handfuls of small rocks wrapped in a paper towel.

Chapter 5: Testing & Function

My biggest success of this whole thing was the breech-loading. I used a modified reducer bushing to pass the barrel most of the way through a larger Tee with a female adapter and a threaded plug on the back. Here’s a video demonstrating it:



Having shot it once in my garage and swiftly coming to the conclusion that shooting this thing in the city was a bad idea, I packed it all up and set off to my friend's house.

One of the big things I was interested in with this project was how effective the dart rounds I made were, so I’ve compiled some of the footage from those in the video below.



Finally, here is the exploding fruit I promised, along with a few other things.



Thanks for reading!
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Moonbogg
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Wed Jan 27, 2021 4:12 pm

Excellent work! I don't think I've ever seen a breech-loading piston pneumatic before. That's pretty unique for a cannon of this size. That's awesome that you pulled that off. Well done.
Regarding your metered propane cannon, I wonder what went wrong there? They are notorious for being consistent, powerful and reliable. What did you think of the hybrid section? Those are pretty intense, right?
headslammer
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Wed Jan 27, 2021 8:05 pm

Moonbogg wrote:
Wed Jan 27, 2021 4:12 pm
Excellent work! I don't think I've ever seen a breech-loading piston pneumatic before. That's pretty unique for a cannon of this size. That's awesome that you pulled that off. Well done.
Regarding your metered propane cannon, I wonder what went wrong there? They are notorious for being consistent, powerful and reliable. What did you think of the hybrid section? Those are pretty intense, right?
The breech-loading was really important to me, I was getting really tired of fussing about with muzzleloading and whatnot.
In terms of the metered propane, I have no clue. My best guess is that it just wasn't mixing with the air in the chamber. I think we waited a bit once and then it worked but I didn't know about chamber fans and the like at the time. Oh well, on to better things now!
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jackssmirkingrevenge
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Thu Jan 28, 2021 3:00 am

Fantastic work!
I’ve always loved tanks and tank combat, so I decided to attempt to make it look like an anti-tank gun, meaning I’d also need to make a mount of some sort.
Something that is immediately apparent, I particularly like the elevation mechanism.

Also the fact that it's breech loading, I was going to ask why the valve didn't dump directly into the barrel.

Great damage footage and nice job on that "APFSDS" projectile!

Are you going to give it a shield and paint job to complete the look, maybe even a muzzle brake?

I am reminded of the WW2 2.8 cm schwere Panzerbüchse 41

Image
hectmarr wrote:You have to make many weapons, because this field is long and short life
headslammer
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Sun Jan 31, 2021 7:36 pm

jackssmirkingrevenge wrote:
Thu Jan 28, 2021 3:00 am
Fantastic work!
I’ve always loved tanks and tank combat, so I decided to attempt to make it look like an anti-tank gun, meaning I’d also need to make a mount of some sort.
Something that is immediately apparent, I particularly like the elevation mechanism.

Also the fact that it's breech loading, I was going to ask why the valve didn't dump directly into the barrel.

Great damage footage and nice job on that "APFSDS" projectile!

Are you going to give it a shield and paint job to complete the look, maybe even a muzzle brake?

I am reminded of the WW2 2.8 cm schwere Panzerbüchse 41

Image
Funny you should mention that. That was my goal for the second iteration of it before I abandoned it for more power. Here's a pic of the design.

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It was fairly advanced, with an electric elevation via linear actuator for -5 to +45 degrees of elevation and a custom-designed hand-cranked planetary gearbox to power traverse, 22.5 degrees to either side. The legs would be stowable, and the wheels would fold down for easy transport, as the total weight was approaching 120 or so pounds. The entire barrel and tank assembly are "floating", mounted on a recoil absorbing assembly that slides backward within the frame, like the M777 howitzer. I might adapt this design to hold a hybrid I'd like to make, I put far too much time and effort into it to totally abandon it lol. I can take more pics if you'd like.
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jackssmirkingrevenge
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Mon Feb 01, 2021 6:58 pm

Very cool... I like the futuristic iteration of what is mostly a dead concept in modern warfare, with the possible exception of the Russian Sprut-B:

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Looking forward to seeing it as a hybrid :D
hectmarr wrote:You have to make many weapons, because this field is long and short life
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mark.f
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Tue Feb 09, 2021 11:57 am

Nice build! Sorry you couldn't get that valve to work, for future reference, a barrel-sealing valve is a lot, lot easier to build (I built my first one and "controlled equalization" with some duct tape and petroleum jelly around some solid PVC rod) and usually performs better to boot (depending on the specifics of piston and porting size).

That said those dust collector valves work really well!
Luke31
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Fri Jun 18, 2021 3:18 pm

Anymore progress on this?
Americannon
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Sun Jun 20, 2021 1:28 am

I like it!
I’m adding 2 more 2” valves to this. 4 2” valves , it’s a beast!
https://youtube.com/shorts/NEpRU3xFAVA?feature=share
headslammer
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Mon Jun 21, 2021 10:43 am

Luke31 wrote:
Fri Jun 18, 2021 3:18 pm
Anymore progress on this?
Sadly no. I had to focus on school, graduating, and now working. At some point, I'd like to get back into this hobby but it's on the backburner for the time being.
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