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more power

Discuss miniature cannons built from things such as pill bottles and pen caps.
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more power

Unread postAuthor: jon_89 » Tue Jun 26, 2007 2:14 pm

i have a 1.5 by 3.5 inch chamber and am currently using propand. is there any way to get more power?
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Unread postAuthor: hi » Tue Jun 26, 2007 2:26 pm

as soon as you describe what propad is. just kidding.

mapp gas is slightly more powerful.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

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Unread postAuthor: jon_89 » Tue Jun 26, 2007 2:31 pm

oops! will another spark gap give it more power?
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Unread postAuthor: hi » Tue Jun 26, 2007 2:37 pm

it might, but its so small you wont even notice, it may be worth a try if you are bored enough. you really cant expect much out of a cannon that small.
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"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote

you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
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Unread postAuthor: Spudgun on Crack » Wed Jun 27, 2007 7:34 pm

YES YES I CAN GET YOU MORE POWER!!!!!!

TRY AT YOUR OWN RISK!!!!!

This is dangerous but the power will be very very powerful.

Ok so you are using propane right, now go to the store and go to the blow torch isle and get the oxygen cylinder. Now mix a little oxygen and propane/mapp gas in the chamber and the force of the combustion may blow off the cap or explode the chamber so you may do this at your own risk!

This will get the most power!
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Unread postAuthor: Arborman » Wed Jun 27, 2007 7:39 pm

oxy enriched mixes and non metal chambers dont go well together.

Enrich and DIE!!

im assuming you have a plastic chamber...
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Unread postAuthor: VH_man » Wed Jun 27, 2007 7:56 pm

spekaing of more power, this would have to be with metal chambers........

has anyone made a combustion powered by white gas?

i treid it once in my PVC combustion (BAD IDEAAAAAAA!!!!!!!!) and i amazingly didnt die/get infused with PVC particles. however, the spud went FAR!!!!!!! it was amazing.

just a thought........ dont try it........ unless you have metal as your chamber
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Unread postAuthor: turbohacker » Wed Jun 27, 2007 8:21 pm

Has anyone experemented with liquid fuels injected through little misters?
Im thinking some oxygen and liquid nitro-methane :twisted:
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Unread postAuthor: VH_man » Thu Jun 28, 2007 8:54 pm

lol. thats a good idea. better than sitting there for 5 minutes waiting for gasoline to evaporate............

bah if only i was allowed to make combustions. id have a Gas-powered marlbe sniper by now.........
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Unread postAuthor: Spudgun on Crack » Thu Jun 28, 2007 10:07 pm

I think that a 3/4inch to 1/2 inch all copper mini will be able to have and oxy rich fuel.

I am off to build one and i will make a topic about this as it does not take that much effort on my part to get a 3/4 in to 1/2in reducer a female adapter for the fuel injection cap in the back.. and a little bit of 3/4in and 1/2in pipe
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Unread postAuthor: Flying_Salt » Thu Jun 28, 2007 10:24 pm

Don't enrich it with a pvc chamber. It will explode. MAPP gas is slightly stronger than propane. Do you have a chamber fan? Those help mix the fuel, even though your chamber is so small it won't change much. Multiple spark gaps can improve preformance slightly but you probaly wouldn't notice.

The best way to improve power would be an insanely thick and strong steel chamber with an oxy/acetylene mix.
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Unread postAuthor: jimmy101 » Fri Jun 29, 2007 12:28 pm

VH_man wrote:spekaing of more power, this would have to be with metal chambers........

has anyone made a combustion powered by white gas?

i treid it once in my PVC combustion (BAD IDEAAAAAAA!!!!!!!!) and i amazingly didnt die/get infused with PVC particles. however, the spud went FAR!!!!!!! it was amazing.

just a thought........ dont try it........ unless you have metal as your chamber


You are doing something wrong if gasoline gave significantly more power than other fuels.

The fuel content, per mole of oxygen required, for gasoline (white or red) is essentially identical to propane. IIRC, the difference in energy is ~1%.

All most all hydrocarbon fuels contain basically the same amount of energy per unit of available oxygen used in the combustion process. The only real outlier is acetylene which has ~15% more energy per mole oxygen than does propane. (Hydrogen is also an outlier at ~15% more energy but hydrogen isn't a hydrocarbon.)
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Re: more power

Unread postAuthor: jimmy101 » Fri Jun 29, 2007 12:39 pm

jon_89 wrote:i have a 1.5 by 3.5 inch chamber and am currently using propand. is there any way to get more power?


First of all what are the other dimensions of the gun and what are your projectiles?

Minis tend to have barrels that are much too small for the chamber volume.

Your chamber is 6.2in<sup>3</sup>. If you are using 1/4" copper tubing for the barrel it needs to be ~10 feet long for a CB of 1.0. It will probably perform OK with a 5~7 foot barrel (CB 2~1.5).

For 1/2" tubing the barrel would need to be 2.5 feet long for a CB of 1.

The other thing that might help would be a chamber fan. If you can fiind a small enough dc motor you can make your own. The tiny vibrator motor used in cell phones works well.
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Unread postAuthor: jon_89 » Fri Jun 29, 2007 8:14 pm

.5 by 18in and i am using either potato or paper darts with a screw for weight
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Unread postAuthor: jimmy101 » Sat Jun 30, 2007 11:56 am

So your CB is about 1.7. A little on the high side but to get a better ratio the barrel would have to be a lot (~2x) longer. And even then the increase in performance isn't going to be a whole lot.

I would think you best chances at improving the performance are;
1. Figure out how to add a chamber fan (hard to do, need a really small motor). Better mixing helps performance and having moving gases during combustion may speed up the burn rate.

2. Try to increase the static friction (particularly with the paper darts). With PVC barrels people increase the static friction by double beveling the muzzle knife so the spud is cut a bit oversize and fits very tightly in the barrel. Combustion guns seem to prefer a fairly high static friction between the ammo and barrel, acts kind of like a burst disk. If your barrel is PVC then double bevel the muzzle. If your barrel is copper I can't think of anyway to get a double bevel to work since the barrel wall is so thin.

Edit:
Sorry, I probably should describe what a "double bevel" is. Normally, you sharpen the end of the barrel (by fileing, sanding, ...) so the muzzle is sharp like a knife. When you shove a whole spud down on the muzzle the sharpened end of the barrel slices through the spud cutting it to exactly the size of the barrel. A double bevel knife means you file down both the outside and the inside of the muzzle. The resulting circular knife edge has a diameter a bit greater than the barrels ID. When you shove a spud down onto this type of cutter the spud is cut large and then compressed down to the barrel ID. For a 2" barrel you can easily get 30 pounds or more of static friction using this method.
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