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Hybrid's Decided it doesnt like working

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's Decided it doesnt like working

Unread postAuthor: spanerman » Tue Sep 11, 2007 5:22 am

Hi, yesterday i was firing the hybrid at 2x mixes and 3x, i have shot at 4x before but not yesterday. Today i loaded up the car with the cannon and accesories and made the trip to my fireing site, set up the cannon as usual, put 21.5 psi of propane in the guage..injected it, added 3 bar of air, armed the cannon then retreated............i pushed the button....NOTHING, i ventet the chamber and repeated.......nothing i tried this 3 times with no avail...the only thing ive done since yesterdays firing is reposistion the ignition box..which meant i had to disconnect the spark box from the spark plug....and i am getting a spark.....HELP this is anoying

i have a meter volume of 40ml and a chamber voule of 308ml....so im 99% percent sure thats right...

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could someone go through the firing procedure i should use in some detail...

best regards Sam
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Unread postAuthor: Fnord » Tue Sep 11, 2007 6:37 am

Well, if you know the fuel mixture is right then the only other thing that could go wrong would be the ignition.
Maybe a rough ride in the car has jolted something out of place inside the project box. Seeing how the wires are taped together, this is fairly likely.
When you tear it down, take off the tape and add some solder or wirenuts. You'll thank yourself in the future.
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Unread postAuthor: SpudBlaster15 » Tue Sep 11, 2007 11:27 am

Your meter appears to be MUCH larger than 40ml. With your design, when you add pressure to the meter, the whole volume between the propane tank and the ball valve directly behind the chamber becomes pressurized. After injecting propane from the section of the meter containing the gauge, I would assume that you bleed the pressure from behind this section using the schrader valve. This leaves an atmosphere consisting of (assuming you have just vented the launcher) 60% propane and 40% air. When you pressurize the launcher to 45psi, this volume of propane is pushed into the chamber, which, depending on the volume of this rearward section) may create a fuel mixture that is too rich to ignite.
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Unread postAuthor: spanerman » Tue Sep 11, 2007 1:20 pm

so what do ypu sujest i do to combat that? and the wires are in terminal blocks just taped to the board
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Unread postAuthor: SpudBlaster15 » Tue Sep 11, 2007 7:04 pm

Change your meter configuration back to the way it was originally (before noname idiotically suggested that you change it), and recalculate your meter pressure for that design.
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Unread postAuthor: noname » Tue Sep 11, 2007 8:08 pm

Now where the hell did I say that? Yes, I told him to try to cut down on meter volume, but that was before I knew you had designed the meter for 4x mixtures. He had it firing fine, with the exact same configuration. Calling me an idiot for suggesting something I didn't suggest is the same as calling him an idiot, because he did it all by himself.
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Unread postAuthor: Pete Zaria » Tue Sep 11, 2007 8:16 pm

Leak test your meter and chamber underwater. A leak would explain why the fuel/air mixture is off and won't ignite.

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Pete Zaria.
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Unread postAuthor: SpudBlaster15 » Tue Sep 11, 2007 8:25 pm

noname wrote:Now where the hell did I say that? Yes, I told him to try to cut down on meter volume, but that was before I knew you had designed the meter for 4x mixtures. He had it firing fine, with the exact same configuration. Calling me an idiot for suggesting something I didn't suggest is the same as calling him an idiot, because he did it all by himself.


You told him to cut down on his meter volume, when all along it was perfectly acceptable to use the configuration he had been using. I said that your suggestion was idiotic, because the only methods that would cut down on his meter volume without necessitating the purchase of a whole new set of parts would simply make the meter even more problematic.
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Unread postAuthor: noname » Tue Sep 11, 2007 9:10 pm

Did he cut down on meter volume? I have no idea.
Did the gun work anyway? Yes.
I changed nothing about his gun. Yet now it doesn't work, so of course, the blame gets passed off on me.
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Unread postAuthor: spanerman » Wed Sep 12, 2007 1:55 am

I can recal someone sujesting cutting down on meter volume...i will change it back but the meter volume was rather large.....and iff i recal somewhere around 70ml....is this acceptable with a 308ml chamber?
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Unread postAuthor: spanerman » Wed Sep 12, 2007 7:35 am

ok, changed meter volume back... its in the original configuration....and its exactly 70ml....what pressure do you guys work out my meter presure should be for a 4x/5x mix? (dont have a go at me i have done the math im just checking)

here is a photo to refresh your memory(yes that is a new stand...
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Unread postAuthor: SpudBlaster15 » Wed Sep 12, 2007 8:04 pm

My calculations are showing ~11psi.
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Unread postAuthor: spanerman » Thu Sep 13, 2007 2:23 am

hmm same hear...seems anoyinginly low.....im going to use hex nipple in my meter over pipe nipple should cut down the volume quite abit....whats your chamber/meter volumes sb15?
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Unread postAuthor: SpudBlaster15 » Thu Sep 13, 2007 10:57 pm

Sorry, I had a mental lapse while punching your figures into my calculator (or as my Math teacher likes to call it, "stupid machine"). The correct pressure for a 4x mix is actually about 13.5psi.

My meter and chamber volumes are almost identical to yours, with my calculated pressure being 14.5psi (due to my use of MAPP gas). I have had no issues with using a relatively low meter pressure. However, an accurate pressure gauge is a must.
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Unread postAuthor: spanerman » Fri Sep 14, 2007 1:39 am

yeah, im going to buy a glycerine filled guage:) and maybe a regulator...
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