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hybrid cartridge protoype without burst disk

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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Unread postAuthor: JDP12 » Tue Aug 17, 2010 11:53 am

hm, I'm actually in favor of SpudFarm's concept there. If you were to sand out the hole for the rod you would get slightly better flow around it... and while the check valve is nice, this seems a heck of a lot simpler.
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 17, 2010 2:11 pm

Right now I just want the bloody thing to work, adding simplicity can come later ;)

I have the prototype cartridge on my desk at the moment and I'm *really* tempted to try it out but the epoxy still hasn't hardened fully and I know better than to take my chances :roll:

edit: tested it for pressure retention, seems to be ok :) here it is compared to a 12 bore shell, hybrid testing tomorrow.
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Unread postAuthor: Insomniac » Wed Aug 18, 2010 1:04 am

It'll sure be nice to FINALLY see something, anything, go POW! :D
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 18, 2010 3:26 am

If only! The damn thing isn't holding pressure, gah this is so bloody frustrating!
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Unread postAuthor: POLAND_SPUD » Wed Aug 18, 2010 3:56 am

Then build a servicable cartridge... just use threaded iron fittings or copper fittings
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 18, 2010 5:45 am

Rather, I will consult courage wolf, who will probably advise me to build something bigger, more manly and less fiddly, as well as disregarding women, acquring currency, studying my enemy, learning his religion and desecrating what he worships, all in appaling English.

I'm also surprised why no one didn't ask "It seems you have unfired 12 bore cartridges, what the hell are you playing about with hybrid cartridges for?" :roll:
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Unread postAuthor: ilovefire » Wed Aug 18, 2010 6:04 am

jackssmirkingrevenge wrote:I'm also surprised why no one didn't ask "It seems you have unfired 12 bore cartridges, what the hell are you playing about with hybrid cartridges for?" :roll:


that did cross my mind when i first saw the picture but i thought it wasn't that constructive to this thread but now you mention it, what the hell are you doing then? :lol:
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Unread postAuthor: al-xg » Wed Aug 18, 2010 6:06 am

no one didn't ask "It seems you have unfired 12 bore cartridges, what the hell are you playing about with hybrid cartridges for?"
... quite the contrary ;)

So that was the lighter/ball bearing check valve combo ?
Where was the leak from ?
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 18, 2010 6:35 am

ilovefire wrote:now you mention it, what the hell are you doing then? :lol:


I'm doing it because I can!

Well, can't at this point :x

It's leaking from the check valve, for some reason. Didn't fire before. Or maybe it did fire without popping the projectile, and the heat from combustion screwed up the seal, fricked if I know.
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Unread postAuthor: JDP12 » Wed Aug 18, 2010 8:07 am

Well it looks cool at least :lol:

Sorry to hear its leaking, but are you thinking of possibly changing the check valve config-- no offense but I don't like the complexity of yours in such an inconvenient to work on package...
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 18, 2010 12:05 pm

Perhaps another major rethink is in order. First of all, hot wire ignition as daccel had used seems to be a better idea than piezo ignition, if anything it should work at any mix number.

It might also be a good idea to go back to the "conventional" way of filling - injecting the fuel first through the mouth of the cartridge, sealing it with the projectile, then pumping air to the right pressure through a schrader valve. When I originally tried this, I couldn't get the right mix. The best logical reason I can think for this is that during pressurisation, fuel was flowing out of the cartridge and back into the pump head. Given the tiny cartridge volume, this would be sufficient to dilute the mix sufficiently to prevent ignition.

I plan to solve this issue by factoring the "dead volume" in, basically the space between the pump head and the pump check valve, when calculating the volume of fuel to inject.

This method should also allow me to reach much higher mixes than I can by manually compressing the mixture with a syringe, which is vital given the small size of cartridge I wish to work with.
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Unread postAuthor: SpudFarm » Wed Aug 18, 2010 12:47 pm

Why don't you just use a small premixed chamber to fuel it? That should be much more reliable and less frustrating.

You could just press the BB in and push the cartrige against the shrader on the premixed chamber.
Just use all brass fittings so there is no chance of a spark when you dissconnect the cartrige.

That's what I would have done atleast.
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 18, 2010 12:58 pm

That will probably be my next move if this doesn't work ;) of course the premixed chamber still needs to be pressurised, but it can be much bigger than the cartridge so the dilution issue shouldn't be so pronounced.

Prototype curing, expect more tales of woe tomorrow :roll:

In the meantime, I calculated that the "dead volume" in my shock pump is about double the volume of my original cartridge, which assuming backflow of fuel into the pump would more than account for an insufficiently concentrated mixture.
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Unread postAuthor: SpudFarm » Wed Aug 18, 2010 2:26 pm

I am looking forward for tomorrow once again :)

How big is the currently curing cartrige? I guess the same size as the one you compared to a 12gauge shell?

Can't wait till I have stocked up my epoxy workshop! To bad I am completely broke right now..

One more thing, can you film your test in HD? I would like to hear the noise.
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Unread postAuthor: jackssmirkingrevenge » Wed Aug 18, 2010 2:44 pm

Since the hot wire ignition allows me higher mixes, I've gone for a smaller cartridge. I tested the wire and it glowed red hot immediately so I'm confident that at least that is ok. Should it work I'll do both HS and HD video. Tonight promises to be a heavy one though so results might take a while :roll: :D
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