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Aluminum Cannon w/ Mixing Piston

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Aluminum Cannon w/ Mixing Piston

Unread postAuthor: auxiliary » Tue Dec 18, 2012 3:58 pm

I built this cannon mostly from scrap aluminum I purchased for $4.50 a pound. I ordered all the other stuff from MSC Direct and McMaster Carr. Plus countless trips to the local True Value hardware store.

Features:

- Aluminum construction
- Manual mixing/exhaust piston
- Piezoelectric BBQ ignitor
- Metered propane fueling (HomeDepotPro's design)
- 2" aluminum cam lock breach
- 1-1/2" sch40 ABS barrel
- ~92 cubic inch chamber

Performance:

I don't have a chrono so I don't know the muzzle velocity, but I think it is about the same amount of power as a launcher of the same size with a computer fan.

The mixing piston is a 4.25" diameter disc of PVC with a bunch of little holes drilled into it. The idea is to mix the air and propane by forcing the gases through these little holes. It also serves as an exhaust piston by pulling in fresh air and pushing out exhaust (see the video for operation).

I would not recommend the piston method because although it simplifies construction, it adds another factor into the fueling process. Let me explain: When I mix the air and propane before the shot, a little bit of the mixture leaks out of the back end of the gun every time a complete a stroke. This dilutes the fuel/air mixture in the chamber a bit. So I have treat the number of mix strokes as another factor in the equation.

I have to do: 20 exhaust strokes, 30psi propane, and 10 mix strokes.

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Attachments
SSCN0659.JPG
fuel meter and regulator
SSCN0660.JPG
regulator on bottle
SSCN0662.JPG
breech (notice barrel continues through male fitting)
SSCN0663.JPG
business end
SSCN0664.JPG
piston handle
SSCN0665.JPG
the cannon!
SSCN0658.JPG
all the stuff
Last edited by jrrdw on Sun Oct 20, 2013 6:28 pm, edited 1 time in total.
Reason: Fixed video.
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Unread postAuthor: c11man » Tue Dec 18, 2012 5:01 pm

I like it!

and the pentagonal end plates with bolts give it one heck of a mean look. How strong of a burst disk do you use?
what are you using as a seal around the piston rod?
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 18, 2012 5:06 pm

I like the post-apocalyptic look, makes a change from the usual PVC combustions :)
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Unread postAuthor: auxiliary » Tue Dec 18, 2012 5:35 pm

I usually just use one layer of printer or notebook paper, but it is noticeably more powerful if I put in 4 or 5 layers of paper. I haven't done any experiments with that yet.

There is an o-ring sandwiched between the rear end plate and the triangle to seal round the rod.
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Unread postAuthor: jakethebeast » Wed Dec 19, 2012 3:01 am

How are the pentagonal plates sealed to the chamber? Solder?

Very nice build!
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Unread postAuthor: auxiliary » Wed Dec 19, 2012 12:48 pm

I made two gaskets out of PVC bathtub liner that I had lying around. The five bolts just squeeze everything together.
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