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Mini Piston Hybrid

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: noname » Thu Jul 19, 2007 10:23 pm

You should use a regular threaded fitting for that. Drilling holes in a pipe lowers its structural integrity.
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Unread postAuthor: PVC Arsenal 17 » Thu Jul 19, 2007 11:17 pm

Balls. All these additions take away the "compact".

How bout tapping a brass coupling?
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Unread postAuthor: clide » Thu Jul 19, 2007 11:52 pm

The idea has come up at least a <a href="http://www.spudfiles.com/spudtech_archive/viewtopic.php?t=1193">few</a> <a href="http://www.spudfiles.com/spudtech_archive/viewtopic.php?t=3550">times</a> <a href="http://www.spudfiles.com/spudtech_archive/viewtopic.php?t=12199">before</a>. It is also the basic idea behind DR's first hybrid except he was using a sprinkler valve instead of a piston.

It should work fine, but a more ideal valve would be something like a <a href="http://www.qsl.net/wb6zqz/dftv19/">DFTV</a>, which is what galfisk used in his valved hybrid.
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Unread postAuthor: chaos » Fri Jul 20, 2007 1:10 am

hmmm... wat if:

instead of having the as would be on a regular co-ax a pressurized pilot area..

with this idea takes out the danger of the pilot air locking the valve shut

ok here goes
you could make a realy nice piston that was "air tight" you would then not have to worry about the pilot locking up and turning it into a pipe bomb,
and to compensate put a spring that will hold the mix before it was combusted behind the valve,
and then "i think" it would work without having to worry about the pilot area locking.

did i make a mistake or would it work? im planning a hybrid soon too :wink:
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Unread postAuthor: PVC Arsenal 17 » Fri Jul 20, 2007 4:35 pm

This is back end I hope to use:

Image

Image

Image


The 3/4" copper coupling fits well into the brass 1" x 1/8" bushing and it will most likely be the are the piston travels in. I will be getting a micro ball valve to prevent the schrader from leaking when the air chuck is disconnected from it.

If I'm going to shoot 1/4" ball bearings, how long of a chamber should I use? I was thinking of using 2, 3" lengths of 1" pipe, connected in the center with a coupling. Since the coupling is thick I can thread another schrader into it for propane filling and also the two electrodes.
I could always use bell reducers and make a shorter but larger chamber.
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Unread postAuthor: wannabie » Fri Jul 20, 2007 4:44 pm

Awww man i was going to do the exact same thing but i was waiting for permition to make a hybrid from my mum..... damn i might still try it though
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Unread postAuthor: noname » Fri Jul 20, 2007 7:14 pm

I'd go with 8-12," so it's not huge, but it's also not seen as some little dinky piece of pipe.
If you're using brakeline as a barrel (I'd use double layered brass), the front bushing will require almost no modification. I thought of this and am using it in making a 1/4" QEV for less that $5. It's simple, and I have no idea how I thought of it (oh, the suspense), but just use a compression fitting.
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Unread postAuthor: PVC Arsenal 17 » Fri Jul 20, 2007 8:34 pm

Brakeline is safe to use up to 1000psi I think.

I found that 5/16" sleeved in some hobby brass tube I got, fits well into 1/4" brass pipe, which fits well into 1/2" copper. So I'll have a lot of soldering to do but it should be decent.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 05, 2007 1:00 pm

Vaguely related question, can you iginite a 2x+ mix with a piezo ignitor?

edit: I know, I know, I should have searched :roll:
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Unread postAuthor: goose_man » Wed Sep 05, 2007 1:59 pm

One problem: how does the mix get past the piston into the chamber. Normally you have an equalization hole, but you can't here.
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Unread postAuthor: iknowmy3tables » Wed Sep 05, 2007 3:18 pm

I thought of the same thing too even the poprelif valve, in fact I heard on a diffrent forum a coaxile piston hybrid has been done before but i have never seen one nor do i know if it used a poprelif

for good results you really should inject the fuel from the chammber

and lower presure pop-relif valves can be found at mc masters
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Unread postAuthor: dongfang » Wed Sep 05, 2007 3:30 pm

Hi,

Great design; I think it will work just fine.

You could always just inject fuel and then air from behind the piston. When you finish with air, the fuel behind the piston will be diluted to eliminate any chance of explosion on the back side of it.

I think the pop off valve will have no effect. Its opening area is 100s of times smaller than the piston area. Suppose you have 3 bars of pressure on both sides of your piston. Suppose it rests 9 centimeters from the breech. At ignition, let´s just say the pressure in the combustion chamber triples. In a static situation and with a very heavy projectile, it would cause the piston to move so that the pressure on both of its sides is adain the same. That will be at 3 centimeters from the breech. That´s going to leave a 6 cm opening!

All this is to say, the piston is going to fly back even without the pop off valve. The compression behind it will even stop it softly again.

Anyway, stand back at a goood distance when testing the "theory".

Regards
Soren
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Unread postAuthor: noname » Wed Sep 05, 2007 9:05 pm

Jack, I fire at 6x mixtures no problem with a BBQ igniter. Just make the spark gap literally as small as possible, as long as you can still see the spark.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 05, 2007 9:48 pm

noname wrote:Jack, I fire at 6x mixtures no problem with a BBQ igniter. Just make the spark gap literally as small as possible, as long as you can still see the spark.


Interesting, thanks for the heads up. I'm tempted to make a 6mm hybrid, for the sake of something different. I would of course be sealed up in a epoxy sarcophogus but I could make the spark gap adjustable, hmmm...
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Unread postAuthor: Novacastrian » Wed Sep 05, 2007 9:55 pm

I use a 2mm spark gap for up to 4x mixes with a piezo JSR :)
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