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hybrid 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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hybrid questions

Unread postAuthor: imthefreak2 » Mon Feb 25, 2008 6:15 pm

hi everyone. Me and my friends are planning to build a hybrid cannon soon and we're trying to get some of the basic parts. We were thinking of getting a sch40 3" aluminum pipe 6061 T-6 for the chamber. Would this be ok and if anyone knows, what's the psi rating on this?
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Unread postAuthor: DYI » Mon Feb 25, 2008 6:21 pm

Steel pipe should work fine for the chamber, and be much cheaper, as well as less susceptible to denting. Unless you're using mixes of well over 10x, you won't need to worry about breaking SCH 40 3" steel, or even coming close to it.
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Unread postAuthor: SpudFarm » Mon Feb 25, 2008 6:27 pm

dyi: why do all experienced members tell higher numbers of what is safe in a hybrid that "ordinary" members?

if it is that way that you have right what will be safe in my hybrid?
(now it is handheld)
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Unread postAuthor: Novacastrian » Mon Feb 25, 2008 8:15 pm

Because experience has taught us that metal Hybrids don't blow up, Fnord tried to DDT a pipe without success, the closest he has come to blowing up his piston Hybrid is when he cracked an end cap (piston caused damage), on top of that the great D_Hall seems to think that unless one were to operate a Hybrid around 30x, the chances of a typically sized spudgun Hybrid DDT'ing are slim to impossible.

If your components are rated to the pressure generally found at a 10x mix you have little chance of being pwned.
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Unread postAuthor: chartreusesnot » Mon Feb 25, 2008 8:35 pm

what can be used to create the spark in a hybrid chamber? If you are using metal, it would be hard to tap and put screws into the chamber...
Also, how does Fnords Piston hybrid work?
I thought hybrids were pretty much burst disk only.
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Unread postAuthor: STHORNE » Mon Feb 25, 2008 8:42 pm

sounds like a kewl idea and for a steel/aluminum cannon, it should be plenty safe.

I say, "GO 4 IT!" :thumbup:
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Unread postAuthor: DYI » Mon Feb 25, 2008 8:47 pm

Nova nailed it. Typically sized SCH 40 steel hybrids will likely fail from pressure alone before you manage to make them DDT by increasing the mix.

Noname did successfully cause DDT in a "hybrid", but that was a 5' long piece of 1/2" pipe with a single ignition at one end and what was essentially a cap on the other. Going by the assumption that DDT runup distance in gaseous hydrocarbons can be directly related to the width of the pipe, we find that the runup distance in a 2" pipe at 6x would be long enough that we have nothing to worry about in most of our hybrids.

Spudfarm, the failure pressure of your chamber pipe is about 2300 psi. So what mix you use depends on what kind of a safety factor you want. 10x mixes would generate something close to half the failure pressure of the pipe.

Chart, to get a spark in a metal pipe, just use a homemade sparkplug. With some HV wire, a pipe nipple (or barb, shrader, etc...), and some epoxy they're quite easy to make. If you can find the taps, you could even use a normal spark plug, but make sure it isn't permanent, because nothing on a hybrid ever works on the first try. And _Fnord's hybrid works a lot like a barrel sealer: you pressurise the pilot to a relatively low pressure (just enough to hold back the mix), then add the mix, and ignite it. The pilot air either vents through a pop-off when the piston moves back, or acts as an air spring to protect the piston housing.
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Unread postAuthor: chartreusesnot » Mon Feb 25, 2008 8:53 pm

oh, so there is only gas on the chamber side of the piston? so on ignition, the pressure would be greater on the chamber side?
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Unread postAuthor: SpudFarm » Tue Feb 26, 2008 2:15 pm

i think it is pretty much like this just that the piston has to pilot itself when pushed back a little.
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Unread postAuthor: kluftern2 » Tue Feb 26, 2008 7:35 pm

hi guys,

I am working with imthefreak on the hybrid and I am having a very finding the necessary parts.

Some parts I am having difficulty finding is

a threaded 3" aluminum sch40 pipe
converters for the valves and barrel
a cheap air tank

We live in San Jose btw but I am fine ordering this stuff online.

Also I am wondering if there are any suggestions on how to make the gun have interchangeable barrels.
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Unread postAuthor: DYI » Tue Feb 26, 2008 8:06 pm

1. As I said before, use steel instead. Far safer, as well as cheaper. If you're really hell bent on using aluminum, you can get it, as well as absolutely any other piece of hardware you could ever dream of, from McMaster-Carr.

2. No idea what you mean there, but whatever it is, McMaster has it.

3. That depends on the air pressure you want. If you already have something good to pressurise it with, you can just get one welded together with some big steel tube. If you want a source of high pressure precompressed gas, you can get all sorts of different gas bottles from your local compressed gas outlet.
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Unread postAuthor: kluftern2 » Tue Feb 26, 2008 8:44 pm

If i went to the gas station and used their air compressor what tank can i get?

Also if I want to reduce a 3" pipe to 1" or 2" what part should I use?
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Unread postAuthor: DYI » Tue Feb 26, 2008 10:14 pm

Your first question is incoherent, and your second question shows a lack of even the basic plumbing knowledge that is essential to building most spudguns. Figure them out yourself.
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Unread postAuthor: MrCrowley » Tue Feb 26, 2008 10:19 pm

kluftern2 wrote:If i went to the gas station and used their air compressor what tank can i get?

Also if I want to reduce a 3" pipe to 1" or 2" what part should I use?


1) Don't build a hybird, not for your safety, but to keep spudguns out of the newspapers and the 6pm news.

2) Don't build a hybrid.

Don't tell me you're planning on charging a hybrid with compressed air at a petrol station?
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Unread postAuthor: Lentamentalisk » Tue Feb 26, 2008 10:54 pm

if you even think of walking down the street on PUBLIC PROPERTY with a gigantic hybrid spudgun, you are not in your right state of mind and should sober up a tad. Then filling it up on SOMEONE ELSE'S PRIVATE PROPERTY with their own equipment, they become liable for what ever the hell you do, and gas stations dont take to kindly to being responsible for people doing stupid things.
Please, for the sake of all of us, get a hand pump and stay in the safety of your back yard.
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