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Semi-auto combustion concept

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: cannon monkey » Thu Oct 23, 2008 12:34 pm

where can i find plans to make one of these?
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Unread postAuthor: starman » Thu Oct 23, 2008 12:46 pm

cannon monkey wrote:where can i find plans to make one of these?


You're looking at 'em. This is a concept discussion.
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Unread postAuthor: Ragnarok » Thu Oct 23, 2008 12:49 pm

Other than being a mind reader so that you can be privy to the full details of the design in my head, nowhere that I know of. If you want plans, you'll have to work from the suggestions of that animation - as starman says, this is a concept discussion.

These ideas may well have been explored somewhere within industry, but the area of semi-auto combustions hasn't really been explored in any great depth on Spudfiles, so there are unlikely to be such plans.
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Unread postAuthor: ramses » Thu Oct 23, 2008 2:33 pm

thanks a bunch, rag, but I would love to see the pressure actuated one.

I doubt I could turn that spool valve down on a lathe, btw. Well, I always wanted a lathe...

may I ask if it draws pressure from the barrel like a gas operated firearm, or something completely different?
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Unread postAuthor: Ragnarok » Thu Oct 23, 2008 3:40 pm

ramses wrote:I would love to see the pressure actuated one.

The pressure actuated one won't prove easy by any means, because it's successful operation will be dependent on many things.

It's sufficently complex in design, manufacture and operation that I want to be absolutely sure the information I'm passing to you lot is entirely correct so it's not misunderstood.

Also, the problem with calling almost any of my designs into my mind is that immediately, my conscious jumps on it, takes it to bits, assesses everything, then suggests something else, so it's still constantly changing - this is all "automatic", it's what my head does.

That may sound great - complete designs for little real effort - but it does it for everything, all the time, and I can't switch it off. This is mostly the reason why I have sleep troubles.

Currently, there are three competing designs within my head, each with their own merits, so I'm going to need to let them stew for a while.
There are also still a couple of problems. Although each of the designs will be capable of rapid fire, none are likely to handle longer periods of sustained fire very well.

As for your last question, no, probably not from the barrel, although there is no eventual guarantee.
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Unread postAuthor: ramses » Thu Oct 23, 2008 6:35 pm

I finally drew up my idea:

sorry, you need to look at it full screen!
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Unread postAuthor: Ragnarok » Thu Oct 23, 2008 6:49 pm

ramses wrote:I finally drew up my idea

I hate to be a killjoy, but I really don't think that's likely to work.

Not only is it likely to dump the new shot of propane during the combustion (however, reverse the locations of the in/out ports, that's solved - i.e. so they're exposed when the valve is the other way to how it is at the moment), and although the barrel pump idea is clever, I doubt that you will able to get sufficient pressure over sufficient time to get it to pump a full stroke.

However, the thing that really strikes me is that piston has no return mechanism.

But sort those issues, that could work as a design.
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 24, 2008 4:17 am

Ragnarok wrote:Safety reasons.


It seems pretty unlikely that anything would happen - how many of us have had a fueled spudgun go off without the sparker operating? What you could do is ensure a good non-return valve is fitted, and maybe include a burst disk in your reservoir that would blow out in a safe direction in case the unthinkable happens.

ramses, it has always been my contention that spudgun designs that bleed air from the barrel, especially with a low pressure combustion, will never work. Remember that automatic firearms using this system have chamber pressures of tens of thousands of psi.
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Unread postAuthor: ramses » Fri Oct 24, 2008 2:43 pm

I realize the problems now and when I get a chance I will correct and re-post.

Edit: revised, and as always, not to scale, layout not final, inevitable changes will be made to allow full use of off the shelf fittings. I see that on McMaster, I will be spending over $30 on check valves alone.

once again, criticize away
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