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first hybrid- a few questions

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: jr » Sun Jul 06, 2008 5:21 pm

From what I see you have a large dead space between the chamber and the projectile which is a bad thing!!!

and the idea of a hybrid is to obtain high pressure (more than a pneumatic) and I doubt that will stem from 30-40psi in the chamber of any hybrid! :lol:
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Unread postAuthor: DYI » Sun Jul 06, 2008 7:28 pm

Contrary to what some people have said, piston valves in hybrids work just fine.

The real trick is to use an air spring, not a coil spring. An air spring is infinitely adjustable, as you only have to increase the pressure behind the piston to use a higher mix. The reason that most people (myself included) don't use piston valves in their hybrids is that they're too damn lazy to build a proper reverse barrel sealer valve.
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Unread postAuthor: jimmy101 » Sun Jul 06, 2008 10:20 pm

burgerace69 wrote:so im just curious, but why dont more people use pistons? it seems like a pretty decent idea (btw i have decided that the chamber be made of steel- everything else can be PVC, dont worry i wont kill myself now)

Like Seaking said, the big problem with a pressure relief valve (which is what burger posted) is that as soon as the pressure behind the ammo is the same as the pressure in the chamber the valve starts to close again.

This is not what you want. You want the valve to fully open at a particular pressure and stay open until manually reset. Or perhaps it stays open then closes by itself slowly, where "slowly" is defined relative to the transit time of the ammo in the barrel.

It can be done, you just can't use a pop-off valve, safety relief valve (like from a water heater), regulator or spring driven piston to do it. You need some way to capture the piston (or diaphram or ...) in the open position.
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Unread postAuthor: DYI » Mon Jul 07, 2008 12:30 pm

You need some way to capture the piston (or diaphram or ...) in the open position.


You could use a burst disk behind the piston. It wouldn't be great for reload time, but it would certainly cut down on foil consumption as opposed to a full-bore burst disk valve.
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Unread postAuthor: burgerace69 » Mon Jul 07, 2008 6:11 pm

so I have looked into parts at the home depot and essentially construced a gun but put everything back. I found a very air-tight yet low friction piston that i could use i've thought about using equal air pressure behind the piston but i cant figure a way to keep it from seeping with time...

Another question: what kind of welding equiptment is cheap and good for copper piping use?
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Unread postAuthor: SpudFarm » Mon Jul 07, 2008 6:18 pm

you can't weld copper (well you can but it is not normal) you solder it
some flux, solder wire and a blow torch and you are done.

"how to solder" on youtube
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Unread postAuthor: clide » Mon Jul 07, 2008 6:37 pm

DYI wrote:
You need some way to capture the piston (or diaphram or ...) in the open position.


You could use a burst disk behind the piston. It wouldn't be great for reload time, but it would certainly cut down on foil consumption as opposed to a full-bore burst disk valve.


Or a DFTV design like Galfisk used on his hybrid.
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Unread postAuthor: burgerace69 » Mon Jul 07, 2008 7:58 pm

WOA! you dont weld copper??? I am a noob at this copper stuff so if i sodder it with flux...will it be able to handle hybrid pressures?


I just watched a video on youtube on how to solder and i saw this bubbling stuff coming out of the hot pipe cracks- is that the "flux"?
(I assume you rub this material on the pipe like pvc cement before fitting the peices and then using the soldering wire right?)
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Unread postAuthor: tyrant_bb » Mon Jul 07, 2008 8:47 pm

Yes, I'm pretty sure copper can handle hybrid pressures...the pipe is rated a lot higher than most hybrids can make.

The flux prevents the copper from oxidizing, solder doesn't stick to copper oxides. I think you also would use certain solder meant for plumbing, because it's stronger than solder for electrics (I think.)
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Unread postAuthor: burgerace69 » Thu Jul 10, 2008 10:02 am

one last thing- say that the piston sticks and the chamber has no escape valve. would it be likely to burst despite brass's high pressure tolerance(with 1x mabey 2x mixture)?
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Unread postAuthor: SpudFarm » Thu Jul 10, 2008 10:51 am

not even a small chance.

(i wonder why we spoon feed this guy how to build the most dangarous gun we can think of)
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Unread postAuthor: DYI » Thu Jul 10, 2008 11:49 am

(I wonder why we spoon feed this guy how to build the most dangerous gun we can think of)


Think of it as assisted natural selection - By helping this guy (and countless other n00bs) build a dangerous device that he doesn't understand, we're actually doing good for the race as a whole. :roll:
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Unread postAuthor: SpudFarm » Thu Jul 10, 2008 11:52 am

lol lol lol DYI :D :D
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Unread postAuthor: psycix » Fri Jul 11, 2008 12:44 pm

DYI wrote:Think of it as assisted natural selection - By helping this guy (and countless other n00bs) build a dangerous device that he doesn't understand, we're actually doing good for the race as a whole. :roll:
Bad side: bad stories about spudguns. People will remind him of "he built a spudgun with help from spudfiles.com and now he is dead."

It may be good for the race, but for the legend of spudding, we'd better convince him to wait some time and work his way up.
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