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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: Crna Legija » Tue Sep 14, 2010 10:32 pm

jackssmirkingrevenge wrote:[youtube]http://www.youtube.com/watch?v=bydZoR1LX0Q[/youtube]

letterbocks.

I'm beginning to think this whole "friction breech" idea is more trouble than it's worth, maybe I should just follow conventional wisdom and find myself some suitably sized threaded fittings...



:shock:
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 14, 2010 11:50 pm

Insomniac wrote:Hey, that's a nice little rocket motor you've got there! :D


Aye, if there's one thing I love about this forum, it's the moral support :roll: :D

This method is too hit-and-miss, threaded cartridges with burst disks are certainly more of a hassle to fill but in the long run probably more feasible. Yes, I will edge towards the dark size and look for suitable threaded fittings that can be bought cheaply and in quantity :?
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Unread postAuthor: POLAND_SPUD » Wed Sep 15, 2010 12:53 am

I'm beginning to think this whole "friction breech" idea is more trouble than it's worth
you might be right. I must be a real PITA to fit a small and working 'friction breech' into a relatively small cartridge.

I guess it makes more sense for typical hybrids. Especially if you want to load ammo from behind to achieve higher ROF
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 15, 2010 1:01 am

POLAND_SPUD wrote:I guess it makes more sense for typical hybrids. Especially if you want to load ammo from behind to achieve higher ROF


The problem as I see it (at least using a length of tube, as opposed to an o-ring/washer in a compression fitting) is that you need to seat the BB fairly deeply in order to resist the chamber precompression, in the case of a pneumatic where constant pressure is applied (ie if you were using it as a detent) this isn't a problem, but in a hybrid where the pressure spike is momentary it simply doesn't work well.

If you're using an o-ring/washer, you need a threaded fitting, so might as well go with a burst disk in that case for complete reliability.
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Unread postAuthor: psycix » Wed Sep 15, 2010 9:28 am

epoxyman wrote:and find myself some suitably sized threaded fittings...

Wait what? Did he really just say... "threaded"...!?


epoxyman wrote:and find myself some suitably sized threaded fittings...

I can't believe it! This can't be right, lets look at it one more time:


epoxyman wrote:and find myself some suitably sized threaded fittings...

My gosh he really said it! :shock:
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 15, 2010 9:57 am

2 Samuel 1:27 wrote:How are the mighty fallen, and the weapons of war perished!


:roll:

I have some 1/8" compression fittings that look like they will fit the bill, watch this space.
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Unread postAuthor: Fnord » Wed Sep 15, 2010 3:09 pm

JSR, I think you might be better off to try that nichrome wire again. If you can't get ignition just up the voltage a little.

Light yellow is epoxy, red is nichrome, green is round stock of your choice OR threared bolt coupling.

If you have a drill press just drill out a piece of round stock. If you don't, just use a coupling and glue the schrader into a slice of threaded rod. Hell, you could just use a thread tap on the inside of a pipe that's about the right size.

(of course, you could also use a piezo with this, but nichrome is easier.)
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 15, 2010 11:49 pm

Fnord wrote:JSR, I think you might be better off to try that nichrome wire again. If you can't get ignition just up the voltage a little.


The problem here though isn't ignition, but valve seal. Still, nichrome would be an easier ignition system to install in a complete launcher because the wiring wouldn't need that much insulation.

Are you suggesting that I just epoxy the projectile in place?

I had though of this option when I first began thinking of hybrid cartridges on spudtech, something like this:

Image

Not exactly quick reload time though, or easily predictable release.

I'm currently making a micro hybrid with a burst disk in a compression fitting, making this for single shots but a cartridge will probably be similar.
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 21, 2010 4:24 am

Posted some development in the mini-hybrid thread but it belongs here really.

Image

It would appear the "non burst disk" idea is feasible with o-rings, but now a question of etiquette, do I stick with the tiny 0.177" BBs - especially after finding out that power is a little on the low side even at 16x from a small cartridge - or do I go for something with bigger balls?
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Unread postAuthor: ilovefire » Tue Sep 21, 2010 4:33 am

how thick are your epoxy plugs? and have you tested it yet? cant wait for a vid

edit; oh right didnt see the other thread
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 21, 2010 4:40 am

ilovefire wrote:how thick are your epoxy plugs?


About 1/4" in this case

and have you tested it yet? cant wait for a vid


No vid I'm afraid, as it can only hold a 4x mix the spark gap is far too small at it won't ignite at that mix. In any case, now that I've gone to 16x I'm not interested in something that low :roll:
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Unread postAuthor: Insomniac » Tue Sep 21, 2010 4:41 am

I would suggest bigger balls.
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 21, 2010 4:46 am

Insomniac wrote:I would suggest bigger balls.


Even before I clicked the link, I knew it would be AC/DC :D :D :D
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Unread postAuthor: POLAND_SPUD » Tue Sep 21, 2010 4:52 am

@jsr
Well if you think of it you might as well build a larger cartridge for 3/8" bbs... Who said it has to fit a pistol ? maybe it wouldn't be a bad idea to build a break barrel gun similar to the M79
That would have both the coolness factor you're after and should be relatively simple to build

anyway something tells me it will be a lot easier to build a full sized loading mechanism first - you can always try to make it a bit smaller but it will be easier to build a full sized one first.
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Unread postAuthor: Insomniac » Tue Sep 21, 2010 4:52 am

What else could I possibly have linked to? To do anything else would be Un-Australian!
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