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Propane Semi Auto Spud Cannon Design Help!

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: spudnutbutthut » Wed Aug 05, 2009 11:04 pm

the gramm3r is due to typing with a wii remote on the internet channel! HAHA!
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Unread postAuthor: spudtyrrant » Wed Aug 05, 2009 11:11 pm

no, he uses a bit slightly smaller drill bit than the 1/4npt threads on the hose barb and the plastic is soft enough to form threads as he tightens it in.

yes, if you look at the picture again there is one right at the front lol.

also, its not going to be semi auto even if you have the constant flow adapters it will fire maybe every 3-5 seconds @ the fastest not including load times and at that rate it will use up a propane tank in under 1-2 minutes
hpa on the other hand would most likely last you 10-15x as long as a single propane tank.
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Unread postAuthor: spudnutbutthut » Wed Aug 05, 2009 11:18 pm

see by semi auto i mean il fire it once every 1-2min, i just dont want to have to get the expensive hps hookup (dont have cash) and propane is just more universal in the airsoft world. If i have a 2in chamber that was like 2ft long how many shots you think id get and at what velocity? APPROX Id be using a nerf rocket maybe.

Id have a 2 inch barrel

You think a 2in chamber is ok or should i go 3 in, il have less shots but more air, which might not even be safe!
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Unread postAuthor: hi » Wed Aug 05, 2009 11:21 pm

at one point, making the chamber bigger doesn't have much of an effect on the power. i think that you should make the chamber of 2'' pipe about 10'' chamber and a 2' barrel and you would be good..

i don't know how much a nerf weights, but i'd say around 250+ fps? just off the top of my head. run it though ggdt.
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Unread postAuthor: spudnutbutthut » Wed Aug 05, 2009 11:23 pm

thats nott too bad, you think itd get any nice range?
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Unread postAuthor: spudnutbutthut » Wed Aug 05, 2009 11:38 pm

hey um, can someone run this through GGDT for me im not to savvy, i tried but it came out with 85/ft sec, lol I dont understand valve fla...w/e.

2 in barrel 2ft, 2in chamber 12"

whatever propane is (custom gas) i think its like 100 psi or 70 idk

Id be launching a nerf rocket, around 150 - 200grams i think

the valves a 1inch sprinkler,

pilot vlave is blowgun

please take a screenshot and post the pic!
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 2:04 am

i know its late but can anyone run this?
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 8:19 am

does anyone haev ggdt and can run a test for me please?
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Unread postAuthor: ramses » Thu Aug 06, 2009 8:39 am

well, I don't normally spoonfeed, but you should get 160 fps with 150gm, 150fps with 200gm. all at 100psi, 80*F

filling the chamber, a 14.9 oz cylinder would give you ~47 shots.
a 16oz cylinder would give you ~51 shots.

The 16 oz cylinders are usually cheaper than the 14.9 oz ones, and are 4 for $10 at my local sam's club.

I really recommend lighting the muzzle blast.
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 9:14 am

lighting the muzzle blast sacres me haha, plus when i fire it itlk be in an arisoft scenario i dont want to siynge people. And if it looks too bad ass they wont let me use i haha!

14.9 arent those the little coleman cylinders?
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Unread postAuthor: ramses » Thu Aug 06, 2009 10:34 am

those are the skinny blue ones commonly sold by bernzomatic for soldering/brazing/playing with torches. the 16oz tanks are sold by coleman and are short, fat and green.

or you could read the label...
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 10:51 am

haha i just did, 50 shots is a lot, hope its true haha!

One more thing everyone I know im being spoon fed but the reason is this cannon has to work...or all my money goes *flush*, after this il be more intelligent and knowledgeable on the topic. ;)

So,

How does the sprinkler valve pneumatic pilot work? If i squeeze the blowgun it will open and then when released automatically close?

My budget is 50 bucks i think il fit it actually!

PVC ~ $25

Disposable Propane Adaptor ~ $7

Sprinkler valve ~ $15

crap,

how much does it cost to modify a sprinkler valve ,like all the clamps and hoses and blowgun etc? I tried looking up the parts but il have to ask in store for em.
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Unread postAuthor: ramses » Thu Aug 06, 2009 1:20 pm

minimum ~$5. 1/4" close male nipple, cheap blowgun.

more if you want a hose. 2-1/4" hose barbs, hose, cheap blowgun. clamps, IDK.

I don't think you will spend $25 on PVC.

The sprinkler should automatically close. if not, you will need to install a compression spring on the pilot side. a pen spring wouldn't have a large enough diameter.
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Unread postAuthor: spudnutbutthut » Thu Aug 06, 2009 1:23 pm

cool thanks, i hear the rainbird is good ima get that.
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Unread postAuthor: jimmy101 » Thu Aug 06, 2009 1:27 pm

spudnutbutthut wrote:haha i just did, 50 shots is a lot, hope its true haha!

One more thing everyone I know im being spoon fed but the reason is this cannon has to work...or all my money goes *flush*, after this il be more intelligent and knowledgeable on the topic. ;)

So,

How does the sprinkler valve pneumatic pilot work? If i squeeze the blowgun it will open and then when released automatically close?

My budget is 50 bucks i think il fit it actually!

PVC ~ $25

Disposable Propane Adaptor ~ $7

Sprinkler valve ~ $15

crap,

how much does it cost to modify a sprinkler valve ,like all the clamps and hoses and blowgun etc? I tried looking up the parts but il have to ask in store for em.

I think you better slow down before your hurt yourself. I know you want to get this done quickly but "quick" and "safe" are not compatable. The gun you are considering is a real gun, it isn't a toy gun like a Paintball or Airsoft gun. Your current design could easily have a muzzle energy about the same as a 0.22 caliber rifle, perhaps even more. Plus, a big time fire hazard and an explosion hazard.

Get a Bernzomatic torch setup (400g blue cylinder + torch head that includes a shutoff valve), IIRC less than $20 from most hardware stores. Forget the propane tank adapter, it'll end up costing more since you still need a shutoff valve on the tank line.

Don't permanently mod the propane torch head, just unscrew the air mixer and connect to your chamber with a piece of suitable sized pressure hose held in place with pipe clamps.

Get a barbed hose adapter (like this)
Image
that matches the hose. Thread the barbed hose adapter into a hole in your chamber.

Get the sprinkler valve, a blow gun and probably a 1/4"NPT male-male threaded adapter (check near the compressors at the hardware store for the adapter and the hose barb).
1/4"NPT male-male threaded adapter:
Image
Blowgun:
Image
The male-male threaded adapter needs to match the blowgun. That's all you need for the valve.

Get your PVC, make sure the pipe is pressure rated (it'll have an actual pressure limit printed on it). Fon't use any DWV only fittings, the kind that change diameter. Get a can of PVC Cleaner/Primer (purple) and a can of PVC glue. You can probably get two small cans as a set.

Get a roll of teflon tape (near the plumbing supplies or compressor supplies). You'll need it to seal the various fittings.

That should get the gun up and working. The torch head still has the flow restrictor and that will slow down how fast the chamber will fill. On the plus side, the flow restrictor significantly reduces the chances of getting liquid propane into the chamber (which would be bad). The propane flow from the tank can be controlled by the torch head's valve.

A 0-200 PSI gauge tapped into the chamber would also be a very good idea. (http://www.harborfreight.com/cpi/ctaf/d ... mber=95447 is a cheap one)

The hose barb and the gauge should be tapped into the chamber through a fitting where you have two layers of pvc (the fitting and the pipe). If you don't have taps you can "ghetto" tap the fittings if you are careful. Drill various sized test holes in scrap PVC pipe and try to thread the fittings in. The brass (bronze, steel, ...) fittings will cut OK threads in the PVC if the original hole is the right size. Once you know what size hole you need then do your chamber. When ghetto tapping the fitting will really want to go in crooked. You have to try to get it to go in straight.

You can remove the torch head and cylinder and reassemble the Bernzomatic torch to be useable. So when you get tired or the gun, or decide to upgrade it, you still have a functioning torch.
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