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propane help

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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propane help

Unread postAuthor: the c3h8er » Fri Apr 06, 2007 5:54 pm

We made a quick propane spudgun and it is not working...basically, all we have is the tip to put the propane in and an ignigition source and no regulaters or gauges. it will not even start. does anyone have any sugestions? oh, and one more question...what are the fans used for? thanks for any help
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Unread postAuthor: hi » Fri Apr 06, 2007 6:10 pm

you probably have to much, some cannons, like mine, only need about 2-3 seconds, any more and its just to much. bigger cannons use more like 5-8 seconds of propane. the fans mix the fuel and air so it ignites better and the cannon is about 1/3 more powerful, it also allows you to be off a little with the propane. when i say a little i do mean a little.
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Unread postAuthor: the c3h8er » Fri Apr 06, 2007 7:03 pm

what r spud bux
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Unread postAuthor: hi » Fri Apr 06, 2007 7:17 pm

they let you buy things, like a signature.

go here-

http://www.spudfiles.com/forums/shop_ef ... ecialshop&
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Unread postAuthor: the c3h8er » Fri Apr 06, 2007 7:32 pm

thx
-what kind of spud guns u got?
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Unread postAuthor: the c3h8er » Fri Apr 06, 2007 7:42 pm

will your fan blades melt and do you use a computer fan or something
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Unread postAuthor: hi » Fri Apr 06, 2007 7:42 pm

Well, i don't know what kind you have, but i like to make the ones that launch potatoes.

ok, ill stop being a smart ass, i have two coaxials, a hybrid, two combustions, and a mystery cannon for the competition. ohh, and a sprinkler valve gun. i have made a couple ball valve pneumatics... its an obsession for me.
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Unread postAuthor: hi » Fri Apr 06, 2007 7:46 pm

no, they wont melt. the chamber is only hot for a few milliseconds, which isnt enough time to melt them. Yes, you use a computer fan. some people use those personal fans from wal-mart, but most people, including me, use computer fans. if you buy one, make sure that is a brushless fan. if it is not a brushless fan dont buy it because it can set off the fuel before you want it to.
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Unread postAuthor: the c3h8er » Fri Apr 06, 2007 8:03 pm

thanks for helping
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Unread postAuthor: frankrede » Fri Apr 06, 2007 10:14 pm

even non-brush less fans won't ignite your fuel.

That is what I heard,
someone did a test I believe.
But get the brush less fans just in case
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Unread postAuthor: hi » Fri Apr 06, 2007 10:18 pm

A non brushless fan is simply called a brushed fan. And yes, it will ignite the fuel. I have seen sparks in the fans. Trust me, i fly rc airplanes and all my brushed motors spark, and all my brushless motors do not spark. maybe its ok on a really small computer fan, but i wouldnt trust it. go with the brushless, they are the same price as brushed and it a whole lot safer.
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Unread postAuthor: jimmy101 » Sat Apr 07, 2007 12:02 pm

I don't believe anyone has ever gotten a combustion gun to fire from sparking in a brushed fan. Too bad really, it would have been an primo ignition system.

DR regularly uses the "personal fans" from Kmart and has never had a premature firing (of his spudgun anyway).

Still, with a brushed fan all the regular gun safety rules should be followed along with treating the fan "on" button as a potential trigger. Just because no one has ever gotten a gun to ignite with a fan isn't the same thing as saying it is impossible.

(Just ask NASA... gee it didn't blow up the last 47 times we launched it so it should be OK the 48th time.)

A fan will increase the performance of a combustion gun more than just about any other simple mod.

The electrical source for most fans is not critical. 12 volt computer CPU fans (brushless) work fine off a single 9 volt batter.

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The most likely cause of your gun not firing is too much propane in the chamber. You only need 4% of the volume of the chamber as propane. Too much (more than ~8%) or too little (less than ~2%) won't ignite.

That brings up the second best mod for a combustion spud gun; a fuel meter. You can build a proper meter with pipe, regulator and valves for perhaps $30.

If you are cheap, and/or you just want the performance benefits of the meter without the cost (or the "blink factor") then use a syringe. For less then $5 you get all the performance benefits of a more complex meter and greater accuracy. See http://home.earthlink.net/~jimsluka/Slu ... zooka.html
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