SpudFiles

Hello Everyone,

I recently built my first combustion cannon and I have some trouble with it.

I did a test run, with no projectile inserted, to see if it actually worked. NOPE!

I have a 2' X 4" chamber with a 4' X 1.5" barrel. With 2 screws through the rear, almost touching. Like they should.

I used the bic stick lighter sparker for a spark. That right there I think is my problem. I used CVS Getto Right Guard. When I have my chamber open, I can see it spark every other click. But after a 2-3 second spray, and a quick seal. I get nothing.

I think my problem is either a weak spark, which I can easily fix by a trip to wal-mart for a sparker. Or Does Weather have anything to do with it? It was very cold (35-30 Degrees F) and on the verge of rain (100% Humitdity!!)


Any help or ideas would be greatly appreciated.

TraLaLa

P.S. Do I need to seal the chamber with a potato for it to work? I left it open as a test run.


*Edit See newest post

I think it is the spark, the piezo you are using is generally used for a mini, like a pill bottle gun. also, I wouldnt fire it when its that cold (at least not with ammo in it) unless you fuel it up and everything inside and take it outside just to shoot, then bring it back in, cold temps can make PVC brittle.

use a stun gun to fire it, that will deffently give you a good spark in a richly fueled inviriment, ebay has got good ones for about 25 dollars + shipping, just be carefull setting it up, mite zap yourself? you can get instrutions from spudwiki, let us know how it turns out

you need ammo for it to work because the fuel is excaping ot the muzzle or some seal to prevent the fuel form excaping but it needs to break when you fire it.

Thanks for the guick responses guys. Cheers

First I will try a bigger BBQ sparker. If not, on to the stun gun.

TraLaLa

P.S. I have a 45 degree elbow at the end to a screw sealed end, that should be no biggie right?


_____________________-----------^]]

Barrel Chamber Elbow Screw-Plug

being a combustion,the problem will be one of these things:

fuel vaporising too fast (too hot)
fuel vaporising too slow (too cold
too much fuel (the most common problem with any
combustion)
not enough spark (also pretty common)
not enough fuel (very rare)
no projectile to hold fuel in (also common)

hope these help!

My gun uses a capasitr and because of the big spark(fling pieses of hot meta in 3s diamerar) it don't jam.It is also very cheap.10 levs=7$

Here are some pictures to give you guys and gals an idea of my situation.

The outside view


The Screws


The Spark


Thanks Again for your help!

looks like maybe your screws are too close together?

id say that the spark is too small in such a big chamber, id add two, maybe three more sparks to that badass.
the 45 wont hurt it at all, makes it easier to refuel from the looks of it.

id use a stungun to ignite that too

Ok, Heres my update.

I got rid of the 1.5" and now I use a 4">3" reducer and about a 2.5 foot long 3" barrel

AND

Instead of using screws from either side i for made a metal box to make a nice big spark. This is inserted directly into the chamber and the wires are threaded through the screw holes. Which I just caulked.

I took a few test runs. Wow....

I used MAPP Gas and let me tell you....That is a gigantic boom. I launched a full waterbottle and that baby soared into the night. I could hear the report echo off the mountains near by. I LOVE IT!

Thanks for everyone for their imput. I will try to post a video of it mighty soon!

Cheers,

TraLaLa

man.. for a combustion that chamber is huge, you'd need a really long barrel for that to be an optimal ratio.
forget using 1.5", it would be too big to hold and you'd need a large stand. probably the same with a 2" barrel.

you probably got lucky and hit a good chamber to barrel ratio (volume) with the 3" barrel however thats going to limit your ammo choices.

i think youd be wise to make a smaller spud gun that would probably shoot harder, look up some info in the wiki about chamber to barrel volume ratios

wow dood quit raining on his parade... obviously he has a great amo that works well with his cannon and he likes it so why does it matter what the hell the C:B ratio is

A chamber can't be too big, with the exception of cases where the increased burn time robs it of too much preformance, but that's quite a bit out there.

Running your numbers through EVBEC (available for download on this site) indicates that you should be able to boost your preformance about 80% (energy wise) by using a 4'x3" barrel instead of the current one.
We are still waiting for the results from the sectional density tests, so that's not certain, but it gives you an idea of what you are missing.
(unfortunatly, that loud bang you seem to like will be gone)

A second ignition point may help too, although that test isn't compleate either.

Edit: Oh, I see you are now using a 2.5'x3" barrel. A 4' barrel would increase preformance ~35%.

Ok, Well this afternoon I to a trip to a little pnd by my house and hammered out a 4 inch thick piece of Ice. I used a hammer and screwdriver to form it to fit snugly down the barrel. A little mapp gas and Blam!!! That 3 pound chunk of ice rocketed about 100 yards. It was still in its upward path when it hit a tree. Yeah.

Cheers,

TraLaLa

P.S. Boiling- Thanks for the info. I know that the loud bang is just wasted energy. But come on, who doesn't love a little pop!