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Replacement for my micro hybrid underway

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Replacement for my micro hybrid underway

Unread postAuthor: inonickname » Sat Dec 20, 2008 6:46 am

Well after only 2 successful tests I accidently dropped my micro hybrid and it got a crack...so not keen on firing it..

And anyway..onto the present. Here's the current progress and plans of my new micro hybrid.

Image
Disks bolted together and a burst disk loaded into position. Taken from barrel side.

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Disks separated, showing where the burst disk clamps and bolt holes.

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Copper disk half. This is the flat side, copper pipe on the other side is attached to barrel.

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Disks bolted together. This is the barrel side, a burst disk is not inserted.

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Copper side of the disk (joins barrel) with a burst disk inserted.

Image

Flat barrel side of the disk. Barrel on the other side.

Barrel, burst disks and chamber joiner:
This is what's complete so far (barrel and burst disk breech). The barrel is epoxied into one of the disks, and the copper pipe (which attaches to the chamber) is epoxied into the other. The flat side of each disk was smoothed with a high grain sandpaper, to provide a tight fit. The burst disk is placed inbetween the two disks, then the short bolts (about 1.5-2 cm) and nuts are tightened with a screwdriver and a wrench. This provides an airtight seal between the chamber, burst disk and the barrel. The burst disks are made from layers of aluminium/tinfoil (a very fine metal sheet used in cooking), amount depending on x used. The barrel's are ideal. I found a huge amount of them at school. They are fairly stiff, minutely flexible. They have thick walls, a slight interior rifling. They cut well, and are not brittle. I have pressure tested them to 150 psi, at which point the cap (homemade) in the end burst out (i think they might be slightly oily/greasy). Also because they are not brittle, they will not shatter and make a heap of harmful shrapnel. They also seem to be moderately heat resistant.
The copper pipe is just plain copper pipe. It connects one of the disks to the chamber.

Chamber:
The chamber is currently unbuilt, but it will need to fill these criteria:

-Can withstand high pressures and heat. PVC is probably out seen as something turned the PVC on my last cannon brittle, and I'm unsure what it was..
-Can be attached to the copper pipe (from gas piping) which will join the disk to the chamber.
-Can be painted/polished to make it look appealing.
-No use of ghetto materials/methods.
-Has a screw in lid to allow for venting/purging inbetween shots.
-Has somewhere to attach a shrader valve, ignition gap and perhaps a fan, depending on size (maybe make a custom fan with a pager motor?).
-Perhaps add a pressure guage, as I'm starting to think the one on the other pump is inaccurate.
-Preferably shorter, and fatter, rather than long and thin.

Ignition:

-Piezo (large one from a hot water system). Reliable, but randomly zaps you and is ugly.
-Maybe a modular stungun ignition that can be moved from weapon to weapon with plugs as needed?
-Disposable camera flash system dumped into a coil.

Mixtures:

Butane:
1x: 3.13% butane, atmospheric pressure.
2x: 6.26% butane, 15 psi.
3x: 9.39% butane, 30 psi.
4x: 12.52% butane, 45 psi.
5x: 15.65% butane, 60 psi.

Propane:
Uncalced..

Chamber volume:
Unknown..


Any thoughts? I think it's looking quite neat so far..and going well.

(I don't blame you if you looked at the pictures and skipped the rest..)
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 20, 2008 6:59 am

A threaded fitting would have provided a burst disk holder that is much simpler to work with and probably a good deal stronger too.
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Unread postAuthor: inonickname » Sat Dec 20, 2008 7:22 am

I'm not sure on that part. My last one used something like that, and it had a heap of problems.

1) due to parts available, I had to use heaps of fittings on the last one. Expensive.
2) it's two sheets of 5mm perspex, and there wont even be a mass of force on it. Strong enough I think.
3) due to having to use a bunch of parts it extended the barrel far too much. Hence why it took me half an hour to get a shot out of the first one.
4) the bolts are the ideal length, only takes a few seconds to screw/unscrew.

Sure, if I lived in a city and had a huge range of parts available, I'd probably find a decent setup. But due to where we live, it's a tiny range of stuff. As in tiny, they don't stock solenoids, banjo fittings or cow bells. It's a very poor range.

Thanks for weighing in though JSR :wink:
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 20, 2008 7:46 am

If it works it works ;) hope you have quality epoxy available though.
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Unread postAuthor: inonickname » Sat Dec 20, 2008 8:03 am

jackssmirkingrevenge wrote:If it works it works ;) hope you have quality epoxy available though.


Well it certainly isn't cheap by anyone's standards. It's the 2-pack stuff that takes a lifetime to dry instead of 5 minutes like araldite, and it reeks.

Good news is I think I found a psi guage :P

Off an old footpump which the pipe is broken on..hopefully it's a goer.

On a completely unrelated topic, mum works as the groundskeeper at the local primary school, and apparently she has a bag of sprinkler valves in which the electrical solenoid part isn't working. Looking good
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Unread postAuthor: ALIHISGREAT » Sat Dec 20, 2008 10:20 am

Copper or malleable iron as i first suggested when you first planned your micro hybrid... *cough* i told you so *cough* :D :wink:
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Unread postAuthor: inonickname » Sat Dec 20, 2008 8:59 pm

Yeh I guess so, but it did hold up ok for an entire 2 shots!
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