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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: spudman029 » Thu Mar 27, 2008 12:04 pm

It seems that these days, most hybrids are being made out of stainless steel or something similar. In general, metal. Back in the day everyone made theirs out of sch80. Did something change? Is sch80 not reliable or safe anymore?

Yes I know that metal is much safer, and can also be taken to higher mixes of 5x-6x. Although most metal parts that are accessable to me only go up to 2" in diameter and I would like a 3" chamber.

Also, I realize that with a metal chamber, a spark plug is needed for ignition. I've never used one on a combustion before, and the search didn't help any. Would it need to be tapped into the chamber? Could someone give me a breif explanation on how they work?
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Unread postAuthor: SpudFarm » Thu Mar 27, 2008 12:15 pm

nice to see that someone else is on the full size trail!
i am going t use my hybrid at 10x so metal is good to 9999999x if you got thick enough walls.

a sparkpug works like this: a wire is slided through an 1/4" or smaller endcap the wire has to be insulated from the rest of the chamber and endcap so the spark will jump to the chamber walls again.

look at advancedspuds.com to get more info..

then look at my signature for the hybrid i am building and to get the reaon i am not explaining so complete :)
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Unread postAuthor: spudman029 » Thu Mar 27, 2008 12:28 pm

thanks for the quick response. i like the size and power of full scale cannons. Massive hybrids were built by DR, jesse spellman, etc...both of which were sch80 pvc. I would like to build a 3" metal hybrid which could also be used as a regular combustion cannon for recreation.

I understand the spark plug now. Generally, do people make their own or will an automotive spark plug work? Also, one electrode of the ignition source would need to be attached to the metal chamber, correct?

Most people are using galvanized sch40 steel. Personally, I hate the way it looks. What about cast black iron?
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Unread postAuthor: Fnord » Thu Mar 27, 2008 12:37 pm

i am going t use my hybrid at 10x so metal is good to 9999999x if you got thick enough

By the way, 9999999x in an average size hybrid would be equivalent to a 20,000 pound propane-air (thermobaric?) bomb going off, but with 10000 times the energy density :).

To answer your questions...

Sch80 pvc was generally abandoned after noname had a hybrid blow up at 2x. It was concluded that pvc fatigues over time because of its brittle nature and will usually fail at some point due to microfractures.

It's still fine for remote firing, but metal is only slightly more expensive and has almost zero chance of failure.

I've always preferred not to use spark plugs, as they require a fairly large hole to be tapped as opposed to one or two small holes (In which case, you would make your own "spark plug" and run wires to it through the holes instead of having the plug itself sticking through the chamber wall.

Edit...
Black iron is basically the same as steel, just with a different enamel/
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Last edited by Fnord on Fri Mar 28, 2008 2:16 pm, edited 2 times in total.
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Unread postAuthor: SpudFarm » Thu Mar 27, 2008 1:20 pm

the "normal" spark plug will be fine..
then i think he can tap a hole like that in steel since he stick to 6x..

if you find a pipe that fits inside your main chamber you can sleeve it and go to10x :)
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Unread postAuthor: DYI » Thu Mar 27, 2008 6:28 pm

Steel is, believe it or not, actually cheaper than PVC for a given size. Whereas PVC fittings have to be bought, steel fittings of nearly any description can be made simply with plates.

As for the safety of sparkplugs; my prototype hybrid has a 1.75" plate on the back where the holes are tapped, so I'm really not worrying.
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Unread postAuthor: spudman029 » Fri Mar 28, 2008 11:48 am

_Fnord wrote:To answer your questions...

Sch80 pvc was generally abandoned after noname had a hybrid blow up at 2x. It was concluded that pvc fatigues over time because of its brittle nature and will usually fail at some point due to microfractures.


Thanks, that cleared it up for me.

_Fnord wrote:I've always preferred not to use spark plugs, as they require a fairly large hole to be tapped as opposed to one or two small holes (In which case, you would make your own "spark plug" and run wires to it through the holes instead of having the plug itself sticking through the chamber wall.


Instead of using the insolated wires as the electrodes for the spark, what about using 2 insolated machine screws or something similar? As long as they are isolated from the metal chamber wall, shouldn't they should be fine in producing a controlled spark inside the chamber?
It would be like using 2 spark plugs meeting each other at the ends, rather than a spark plug sparking against the inside of the chamber.



Also, most people have their meter system connected to the end of the chamber via a threaded reducer or reducing bushing. With this closing off the chamber other than from the barrel, how is it possible to vent the spent gasses quickly enough for another shot? Can you still use a chamber fan inside of the enclosed chamber? Even so, it would be difficult to repair the fan if it broke.
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Unread postAuthor: SpudFarm » Fri Mar 28, 2008 11:53 am

just try your ignition system on a steel plate and find a selution that is good for you ;) ;)
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Unread postAuthor: spudman029 » Fri Mar 28, 2008 12:03 pm

Ok...any ideas about the exhausting?
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Unread postAuthor: SpudFarm » Fri Mar 28, 2008 12:46 pm

if you mean burnt gasses just rush the chamber in 1 second from your air source.

on a hybrid you don't need to vent but you get a weak(er) shot if you uses just the compressed air.
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Unread postAuthor: Jared Haehnel » Fri Mar 28, 2008 12:58 pm

i am going t use my hybrid at 10x so metal is good to 9999999x if you got thick enough walls.


You can do that with just about any materials as long as it "thick enough"

Any one tried using wood before?
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Unread postAuthor: LikimysCrotchus5 » Fri Mar 28, 2008 1:27 pm

Well IIRC, i think spudfarm made a wood combustion, but i know a wood combustion has been made before.
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Unread postAuthor: starman » Fri Mar 28, 2008 1:51 pm

LikimysCrotchus5 wrote:Well IIRC, i think spudfarm made a wood combustion, but i know a wood combustion has been made before.


The only one I'm aware of is Eddbot's hilarious wooden adventure here

http://www.spudfiles.com/forums/wood-co ... 12766.html

even earned Gort's ghetto award...
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Unread postAuthor: LikimysCrotchus5 » Fri Mar 28, 2008 1:53 pm

Ahh thats right the pink elephant :)

Thx, i remember now.
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Last edited by LikimysCrotchus5 on Fri Mar 28, 2008 2:57 pm, edited 1 time in total.
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Unread postAuthor: SpudFarm » Fri Mar 28, 2008 2:32 pm

haha i started thinking when i saw that i had maked a wood combustion :P
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