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Hey guys, Newbie here, any first-timer advice?

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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Unread postAuthor: OneIntervention » Fri Jan 06, 2012 11:38 pm

Actually, I was planning on using Axe :roll:

So when I have the chamber volume, I get 3% of it, fill that much of it with butane in the syringe, put that through a hole in the back, and I'm good to go? Sounds good.
EDIT: Forgot to screw the hole shut. My bad :lol:
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Unread postAuthor: jackssmirkingrevenge » Sat Jan 07, 2012 1:53 am

OneIntervention wrote:Actually, I was planning on using Axe :roll:


BOOOOOO!!!!

So when I have the chamber volume, I get 3% of it, fill that much of it with butane in the syringe, put that through a hole in the back, and I'm good to go? Sounds good.
EDIT: Forgot to screw the hole shut. My bad :lol:


I presume you're referring tomy video tutorial. You don't really need a hole in the back, if your projectile is reasonably airtight you can squirt the butane into the barrel directly before ramming your projectile in. I used a separate fuelling hole to show the chamber volume before calculating the amount of fuel to be used.
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Unread postAuthor: Moonbogg » Sat Jan 07, 2012 2:42 am

If you plan on using any kind of clean gas (propane, butane etc) consider at least adding a chamber fan at a later date. You are likely to be curiously shocked at the increase in power from just the fan alone. Sorry, I know I keep pushing you to add stuff to this thing like a sneaky pimp.
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Unread postAuthor: OneIntervention » Sat Jan 07, 2012 12:39 pm

@jack,
For some reason I can't watch that video, it says EMI records has blocked it on my country :roll:

@Moonbogg,
Yeah, I'm looking into a fan, my only worry is that it'll break, but it seems everyone's reassuring it won't, so I guess I don't have to worry about that.
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Unread postAuthor: jimmy101 » Sat Jan 07, 2012 12:51 pm

OneIntervention wrote:The only problem with that is then butane or propane would probably be involved, and I don't know about that kind of thing before I've got my feet wet.
Since you have to have fuel ...
and a meter is by far the most important component of a combustion spud gun ...
and a suitable syringe costs a buck or two ...
and a fuel source costs 99 cents ...

read http://www.spudfiles.com/spud_wiki/inde ... Fuel_meter
Image Image
On the left is a syringe connected to a $0.99 butane lighter, on the right a butane refill cartridge that probably cost $2. The lighter will give you a couple dozen shots, the refill some thing like a couple hundred.
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Unread postAuthor: OneIntervention » Sat Jan 07, 2012 12:56 pm

Hmm, I think I'll use the method on the right, plus a hole in the back. That seems a bit more accurate rather than jamming the projectile in after putting the butane in the barrel.
Actually, that method doesn't seem too bad. I'm not breech-loading anyways, so it would be a bit integrated. Plus I don't like the idea of screwing the thing shut every time I want to load, that's some more time in the reload time :roll:
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Unread postAuthor: Gun Freak » Sat Jan 07, 2012 2:30 pm

I think I'll use the method on the right, plus a hole in the back. That seems a bit more accurate rather than jamming the projectile in after putting the butane in the barrel.

Don't leave a hole in the back of your gun... That's stupid. You can at least use a small ball valve to open to inject fuel then close it to fire. But, putting the fuel in the barrel then pushing the projectile down does aid in mixing if you're not going to use a fan. But if you're using a fan then go with the ball valve.
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Unread postAuthor: OneIntervention » Sat Jan 07, 2012 2:33 pm

I was planning on screwing the hole shut, but the ball valve idea looks pretty neat. And with that, I'd be able to use the fan :D
Now all I have to do is get some materials...
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Unread postAuthor: jimmy101 » Sat Jan 07, 2012 3:27 pm

More overkill.

Just get a needle (or use a couple inch length of small id hose, perhaps the insulation from wire) on the syringe. Load the ammo. Point the gun down. Lay the clean out cap on the opening. Pass the tube (or needle) through the small gap between the cap and the fitting. Squirt the fuel in. Pull the hose/needle out. Screw the clean out cap in place. Run the fan (the second most important feature of a combustion spud gun) a couple seconds. Fire.

Propane and butane are both denser than air and will, initially, tend to sink down into the chamber instead of escaping back out the opening between the clean out and fitting.

If you really want an injection port, a tire stem is excellent and cheaper than any valve (figure a tire stem costs $1, or less). Install the stem in the chamber then use a stem removal tool to take out the valve. The plastic screw on cap that came with the stem is more than adequate to seal the chamber after injecting the fuel, no need to reinstall the valve. The opening in the stem is big enough to pass a needle or small OD tubing.
Image
You can get fancier stems, like metal truck tire stems.
Image
That's a chromed tire stem with chromed metal cap (that even had a gasket) on the left end of the chamber under the curved part of the blue wire.
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Unread postAuthor: OneIntervention » Sat Jan 07, 2012 3:38 pm

That looks fantastic, however then it would be self-redundant if I wanted to open the back of the combustion chamber using a ball valve or something to vent the exhaust fumes out of the chamber, I could just do the syringe injection into the open chamber after having vented out the exhaust using the fan.

Also, is propane and butane lighter or heavier than air?
EDIT: Sorry for the stupid question, did some Googling and found I don't have to worry about my fuel floating out of the chamber :roll:
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