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Handheld Adv. Comb. Golfball Cannon, underway!

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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Handheld Adv. Comb. Golfball Cannon, underway!

Unread postAuthor: JET47 » Thu May 22, 2008 9:57 pm

Ok guys, I'm working on my first combustion cannon. Golfballs as ammo, breech-loading ball valve mechanism, not what the term for that is. Made a quick flash diagram just now below.

It's supposed to be handheld, I've only bought a few of the parts as of yet cause of money and wariness of purchasing unneeded things, wanted to show yall the plans before i spent anything serious.

I've got a couple questions on the design I havn't quite worked out.
First, i wanted to make the chamber a 2" diameter, instead of 4", but im worried about finding a fan that'll fit.
I'm also not sure how the zapper ignition will work. I read a topic where the guy had instructions on how to mod it, sorry i can't remember the name. I had one of the old ones, before they changed em for safety, that was just one grill- every other bar was connected to one side, etc- that i modded a long time ago into a stun prod. So i've got the innards from that ready, except to my knowledge zappers don't spark merely from being close together. maybe the jump to a 9v power source will do it, i dunno. its always seemed to me that the buttons got to be pressed, then the leads need to be bridged. and the thing about residual charge, i don't really see how theres a risk of it setting off the fuel, unless its that surrounding it with something a little more substantial than air will be enough to cause the jump.

Ok sorry for the zapper rant.
was also wondering about my propane meter, thats the bit i'm least familiar with. the female socket on the regulator and the male head on the propane tank aren't really a nice fit =P so i guess i'll just have to find adapters that'll work? I'm thinking theres a part that makes the necessary adaptation and has a valve for opening and closing the tank with its little nipple that i just havnt seen anywhere. and i haven't a clue how i'm going to go from the regulator to my PVC meter. maybe a really short hose?
And to change out the propane tank when it gets low, i was thinking of adding a quick-connect valve, but i dont know where i should put it.


Ok. I havnt cut the barrel or the chamber or the little chamber for the meter yet, as i havnt yet made any calculations. I'm concerned my barrel and chamber sizes r just so low that I won't get much power, even though the ratio will be on par. and yes, I know this will probably sound like a bomb going off =P

Thanks for reading all that
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Unread postAuthor: FordGtMan » Thu May 22, 2008 10:03 pm

Are you sure that a golf ball will fit in that ball valve? I think the ball of the valve doesn't have a diameter of 1.5 " like the pipe, but im not sure. You might want to look at the breech loader BCarms has.
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Unread postAuthor: JET47 » Thu May 22, 2008 10:09 pm

heh, the only part ive actually made already is that valve. used a 2" ball valve, which is why the 1.5 SDR is inside of it. works perfectly, except its really tough to turn it from the close position. I think i'm going to add an arm on to make it easier once its actually on the gun.

The 1.5" is sleeved in 2" pressure rated on both sides, saftey i guess? even though its supposed to be ok. I've only ever worked with pneumatic and its not fun when they blow up unexpectedly.
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Unread postAuthor: Sergeant Dotson » Thu May 22, 2008 10:13 pm

Correct Ford, the ball valve does have a smaller hole than the pipe. That will leave you with a little more rethinking...

EDIT:

If the 2" works, but is hard to open, put some vasoling on the ball of the ball valve while it's closed. Then open and close it a few time and it will open as fast as you can turn it. :)
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Unread postAuthor: starman » Thu May 22, 2008 10:40 pm

Looks like you are generally on the right trail. If you want to keep the gun handheld size, it will almost by default be somewhat underpowered for golfball sized ammo. However, it should still have enough power to have some fun with.

I would go with 2 1/2 or 3 inch stubby (maybe 6 or 8") chamber instead of the 2"... will help get some volume in your chamber. 2" just doesn't offer the volume. 3" should still be compatible with handheld rifle size and can put the smaller CPU fans in there.

However, it's your GB gun....do what you want with it....keep us posted on your progress.
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Last edited by starman on Thu May 22, 2008 10:42 pm, edited 1 time in total.
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Unread postAuthor: JET47 » Thu May 22, 2008 10:41 pm

thx didnt think of lubing it =P

i've got an almost full tube of white lithium grease i'll use instead of vasoline, easier to clean up.
it did wonders for my piston coaxial.

took some pictures of the valve, ill add them


EDIT: wow 3" never even crossed my mind haha. that would prolly work, except id have to buy a 10' peice for 20 odd dollars, and i have yet to check the local radio shack for what fans are available. im from the virgin islands its miserable to try and get anything specific down here.
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Unread postAuthor: starman » Thu May 22, 2008 10:50 pm

Nice job lining up the golfball hole with the valve hole...looks perfect from the picture. Did you use a forstner bit and a drill press to drill it?

JET47 wrote:EDIT: wow 3" never even crossed my mind haha. that would prolly work, except id have to buy a 10' peice for 20 odd dollars, and i have yet to check the local radio shack for what fans are available. im from the virgin islands its miserable to try and get anything specific down here.


Nah, both Home Depot and Lowe's have 2' lengths of 3" PVC..."project pipe" something like they call it. Seems like $5 or so. Just have to get the proper bushings to fit it all up right. Just be sure whatever you get is pressure rated pipe. Much of the 10' sections they sell are no longer pressure rated.
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Unread postAuthor: JET47 » Thu May 22, 2008 10:55 pm

i used something like a forstner, its ancient though not as spiffy as they are now. but it was a tad small, widened it a little with a dremel
havnt got a drill press though, had to just do it by hand. marked a dot in the center by eye and drilled a pilot, got lucky i guess.

EDIT: looked it up, called a holesaw lol, i actually think its the same one as in the picture on wikipedia

EDIT: ive read about those 2' peices, and im jealous, cause they dont seem to have them at our home depot =(
ive gone there about an average of every other day for the last few weeks haha, spudguns are fun =P
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Unread postAuthor: starman » Thu May 22, 2008 11:01 pm

JET47 wrote:i used something like a forstner, its ancient though not as spiffy as they are now. but it was a tad small, widened it a little with a dremel
havnt got a drill press though, had to just do it by hand. marked a dot in the center by eye and drilled a pilot, got lucky i guess.

EDIT: looked it up, called a holesaw lol, i actually think its the same one as in the picture on wikipedia


Actually a holesaw may work better for this application. You did a good job with it!
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Unread postAuthor: starman » Thu May 22, 2008 11:04 pm

JET47 wrote:EDIT: ive read about those 2' peices, and im jealous, cause they dont seem to have them at our home depot =(
ive gone there about an average of every other day for the last few weeks haha, spudguns are fun =P


Where are you located?

Edit: Sorry you mentioned Virgin Islands earlier. Find you local industrial plumbing supply store then...they will have pressure rated pipe. Maybe you could order a 5' piece from McMaster.
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Unread postAuthor: JET47 » Thu May 22, 2008 11:17 pm

ahh that would require shipping =P

anyways, im still stumped about the propane meter.

every time ive tapped metal guages or threading of any type directly into PVC its leaked, so im a little wary of that.

and i cant think of anything to go from the regulator to the first ball valve except using a tiny bit of hosing
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Unread postAuthor: starman » Thu May 22, 2008 11:25 pm

JET47 wrote:ahh that would require shipping =P

anyways, im still stumped about the propane meter.

every time ive tapped metal guages or threading of any type directly into PVC its leaked, so im a little wary of that.

and i cant think of anything to go from the regulator to the first ball valve except using a tiny bit of hosing


Brass hose barbs on the regulator and the ball valve sides, hose clamps and an appropriate length of hose depending on your mounting configuration....is the typical method.

Use teflon tape or pipe dope on ALL threaded connections and tighten hose clamps very tight! Gas will leak from all that stuff if you don't.

Here's a close look at my setup

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Unread postAuthor: JET47 » Fri May 23, 2008 12:47 am

ok, ive been convinced to go with an all metal meter. and i guess ill have to buy a threading tool >.<

ive been hand threading best i can just using nipples forcefully twisted into pilot holes.

i want a quarter inch npt right?

EDIT: just got back from radioshack, bought an 80mm fan so i can do 3" chamber. and a switch and a few 9v battery snaps, so i'm going to try to make a handle to hold all that.
i jury rigged a spark strip with some quarters and a piezoelectric sparker just for proof of concept, it was hard to get it to work with 5 or 6 of them, and the spark was tiny. thats to be expected right? that as u increase the number of gaps, the spark gets smaller, and (maybe) they have to be closer together?
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Unread postAuthor: jimmy101 » Fri May 23, 2008 10:15 am

JET47: That mod'd ball valve was beautifully done. The gun looks very good.

The size of the sparks really does not matter. Big fat sparks, tiny little sparks, ... they'll all ignite the fuel which is all you care about. If you use pointy electrodes you can get away with a larger total gap length, or, the same total gap length will spark more reliably.
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Unread postAuthor: starman » Fri May 23, 2008 10:29 am

JET47 wrote:ive been hand threading best i can just using nipples forcefully twisted into pilot holes.

i want a quarter inch npt right?


1/4" NPT for all the chamber connection and propane regulator assembly but I used 3/8" ball valves and 3/8" for the meter pipe. FYI, 3/8 pipe is actually 1/2" inside diameter. When calculating meter volumes be sure you work with real world pipe dimensions and not the advertised "size".
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