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Airgun
About

I am making an airgun, which uses compressed air to launch a small object, such as a marble. I plan to loosely base my design off of the one at this site, but will have to live with whatever parts I can find, or buy cheaply at Home Depot. So far, here is what I've got:

  • Barrel: 3/4" copper pipe, 3 ft long
  • Air tank: 1 1/2" PVC pipe, 3 ft long
  • Valve: Standard 3/4" gas cutoff valve 3/4" full port brass ball valve 3/4" pneumatically triggered sprinkler valve
Pics
The new sprinkler valve with blowgun pilot and optional electric trigger
The whole gun showing the new valve
Scrap piece of plywood as target (it has spraypaint on it)
A marble entrance hole (there is perf board behind it)
and exit hole
Colored spots from firing M&Ms in shotgun blasts

Old Pictures of previous designs

Videos

Part 1:

Part 2:

Updates/Progress

  • So far so good. I have tested it opening the valve manually, and it can fire pretty far (100m?). At 100 PSI (I'm using metric everywhere else, I suppose I should convert this into KPa), I shot it straight up, and it took 8.45 seconds to hit the ground again. Assuming the projectile (AA battery) was perfectly aerodynamic, the gun fired it at 41.14 m/s, and the battery reached a peak height of 87.47 m.

  • I didn't realize how many of this guy's ideas I would copy, until I noticed how good some of them were. For my trigger, like him, I am latching the spring with a hook. I originally tried making an aluminum piece to catch the valve, but 1) it didn't latch well, and 2) it was impossible to fire when it did latch.

  • The project is not complete yet, because I have not had a successful trial with the new release mechanism above 80 PSI. At 80 PSI, the battery probably went 125m. On every other trial, the valve hasn't flipped all the way, and you got a loud hissing sound, and the projectile sort of fell out the end. To fix this, I stretched the spring more and made it so more of the force works towards flipping the valve all the way. When it still wasn't working, I tried spinning the ball valve around in a drill. It got pretty warm after a minute or two, so I stopped. I tried it out, and now it is actually harder to turn than before. I may need a new ball valve, or some other valve that turns quicker. At least the valve is easy to remove, since it's threaded and not soldered. I am hoping to simply design a new lever for the valve out of aluminum, in which more of the spring's force can be used opening the valve.

  • Note on power: I was able to put a marble through 1/4" perf board at 100 PSI flipping by hand

  • I have now perfected the valve release mechanism, using a new better ball valve (full port, made for water). It can put a marble through 1/2" plywood.

  • Of course, I always want bigger and better, so I decided to ditch the ball valve design for a much better choice: a diaphragm valve. I stumbled across it here. After ordering it and waiting a while, I modded it for either pneumatic or electric operation. It was the "wrong type", with the guide rod on the top, and not enough space to drill a hole. My solution was to epoxy the guide rod onto the bottom, instead of the top, leaving the top open for drilling.

  • I had some fun today testing the new valve. My 1/2" plywood target now has so many holes in it that I can't tell where the marbles are going. I also tried firing a smarties pack (exploded and sent dust everywhere), and M&Ms (leave colorful marks on plywood). The blowgun pilot valve is much more natural to throw than the old ball valve spring trigger (sorry I never got any pics). A video for this airgun is imminent.

  • My plan for the future is to construct a better airgun in a few months: I will put the ball valve trigger mechanism back on this one, and put the sprinkler valve on the new one. I plan on making the new one have a smaller chamber (there is a lot of wasted air on this one), being all PVC (easier to work with than copper), and being breech-loading. I'll make it more natural too, with a wood stock and a convenient trigger.

Status
  1. Get Parts
  2. Assemble Parts
  3. Test with manual valve release
  4. Design valve release mechanism
  5. Try with modded sprinkler valve
  6. Test again, debug, modify
  7. Video