Calling all spud-gun makers

[zahc]

For the basic aquanet cannon, what volume ratio do you want to have between the fuel chamber and the barrel? I seem to remember being told a rule of thumb, but I don't remember what it is.

[K Frame]

Aquanet?

My friend Dave and I use engine starting fluid.

Ether.

We threw some spuds well over 150 yards yesterday.

When you get the mixture right, it sounds like a .22 going off.

Of course, the entire firing chamber is wrapped in fiberglass strapping tape.

Just a word...

If you're going to make one of these, make damned sure that you use the PVC tubing that is rated for high pressure. There are types on the market that have a LOT of bubbles in the matrix, which makes it lighter and cheaper to make, but it's not rated for the kind of pressure pulses that a spud gun will produce.

Remember, too, that your spud gun is like a car. When it's cold, it requires more fuel to fire -- a richer mixture. When it's hot, it needs less fuel.

[charby]

I was going to make a spud gun after shooting my friends. His was 18" X4" PVC for the expansion chamber and 24"x 2" for the barrel. Launches a spud about 150'.

Then his cousin brought out a 2" cannon.  Screw the spud gun, I'm saving up for a mountain howitzer. In about 5-6 years look for my post on the range test.

-C

[publius]

I use a one foot section of 4" pipe for the combustion chamber, and about 4' of 2" rifled PVC (available from spudtech.com) for the barrel.

For ignition, lead two heavy wires through a hole into the combustion chamber and seal the hole w/epoxy putty. Wrap the other ends around the chamber and secure them to the outside w/ends exposed. Get a stun gun, and touch the probes to the wires. It makes a great spark!

BTW, "Oops!" brand carburetor cleaner or any engine starting fluid works better than even the best hair spray. Green oranges of slightly greater than 2" diameter fly better than taters. We've gotten them to fly about 300 yards, and shot them vertically with a hang time of 16 seconds.

[TMM]

to answer your precise question, i believe the barrel:chamber ratio is 1.5:1.

any longer the barrel, it slows down with friction and the gasses have mostly already expanded.

any shorter, it would be louder and lose efficiency.

perhaps a 2:1 ratio would be ok, i'm not sure[it would be quieter, at least] - perhaps you could make an extra long barrel and cut it down until you find the optimal length.

~tmm

[Sylvilagus Aquaticus]

My preferred method is a ratio of roughly 1 to 4 for combustion chamber to barrel length. My Old Reliable is actually 12 inches of chamber to 4 feet of barrel at the neckdown collar. All were made from Schedule 40 or better. Been building them for about 17 years now.

I've used both Coleman lantern sparkers and piezoelectric bbq grill igniters with good success. Of course, the pushbutton method of piezo is more consistent, from my experience.

I've made several with 2 inch diameter barels, but I've had excellent results with 1 1/4 inch dia. barrels as well. Just about perfect for use with a foosball, which WILL penetrate 1/2 inch plywood at a scary distance.

And, in closing, starting fluid/ether is the best propellant I've run across for casual use. Aqua Net tends to leave a gummy residue that coats the insode of the chamber, ignitor, and plug threads. Probably has something to do with the plastics and lacquer in it.

Regards,
Rabbit.

[stevelyn]

I've found that a little spritz of ether is the perfect and clean buring fuel.

The combustion chamber should be about 22"-24" x 3". It should also be made of ABS rather than PVC. Same with the reducer and screw cap.

The barrel should be 40" x 1 1/2" and can be made of PVC since it dosen't have to contain pressure spikes.

[Harold Tuttle]

i run pneumatics



http://www.bavetta.com/aircannon.html

[Ben]

Aquanet?

My friend Dave and I use engine starting fluid.

Ether.

Well? It's ether Aquanet or starting fluid. Make up your mind!

[Guest]

If you are going to piddle with higher octane fuels, i recomend building your spud cannon with ABS piping.  doesn't shatter/fail under pressure as PVC can.  little more spendy, but after blowing up one PVC gun, I go the extra 20 bucks for the good stuff.

[Azrael256]

If you are going to piddle with higher octane fuels, i recomend building your spud cannon with ABS piping.

Pfft!  Build it out of drill stem.  With some drill stem, old Caddy parts, a welder, pyrodex, and plenty of beer, you too can build an extremely dangerous cannon that the Sheriff will ask you to stop shooting because you're a drunken redneck idiot bent on accidentally killing yourself.  Substitute some acetylene for pyrodex (and sober up) and he'll cool off about it and maybe even ask to shoot it.  Use electric window motor parts for a T&E mechanism, weld in a piston (after some grinding) for a breechplug and firing chamber all-in-one, and set the puppy off with a rocket motor igniter.  You'll need a wiring harness or two to make a long enough ignition wire that you can run it into the trench.  You'll definitely want the trench.

[Guest]

i run pneumatics



http://www.bavetta.com/aircannon.html

I visited a friend's place the other day and saw his pneumatic cannon at work. What a machine!

He owns a stainless-steel fabrication business, so it was made, naturally, of stainless tubing. It has a large reservoir under the barrel - about 4 inches diameter, two feet long. The barrel is a smooth-bore, about 3 feet of 2.25 tube. The reservoir is filled with a standard compressor to 100-120 psi. There's a 'dump valve' between the two, with about a one-inch flow pipe. The valve is used in "bag house" dust collection systems; he buys them by the hundreds. As long as pressure is maintained on the valve's operating port (keep your thumb on the end of the small hose) the valve is closed. Release the pressure, and the valve 'dumps', firing the cannon.

This thing launches things in a spectacular fashion. I watched a wooden plug - or tried to - get launched and saw a brief blur, followed by a toilet-paper wad (projectile was too small). They fire ears of corn, with the husk pulled back to act as a stabilizing fin. They travel 2-300 yards but have a spiral trajectory from the 'fins'. A hard rubber ball will penetrate 3/4 inch plywood at 50 feet.

The thing is very dangerous. That's the sort of stuff they do, though.

JB

[Harold Tuttle]

cool!

i would love to get a part number on the valve he runs...

heres my new test rig:

[Marnoot]

Harold, I'm very interested in what you're using for a tank, valve, and trigger mechanism there. My pneumatic's PVC reservoir makes me nervous. I've just been using a sprinkler valve that I operate electrically for my trigger mechanism. What's the white squarish piece at the back of the barrel there?

[Harold Tuttle]

thats a Zoeller gate valve:
http://www.acehardwareoutlet.com/(fvig3s55gqqswaiyuwvqbs45)/ProductDetails.aspx?source=aceoutlet&SKU=4114757

the main air tank is a interspiro tank from a firefighters airpack

its rated to 4500 psi


my design is based on this one:
http://www.antennalaunchers.com/csv19/index.html
but i run my pressure in via a palmers stabilizer

[BillBlank]

*Bill walks into tomorrow's tech lesson "hey kids, screw the crappy rape alarm, lets build something cool."

In my dreams.

What I do in my spare time is my own business of course.  

Nice toys gents, I'll try not to blow my hands off.

[Marnoot]

What is the purpose of the gate valve?

[Harold Tuttle]

thats my breech load for nerf mini vortex projectiles

the unit is designed to hork them at 230 fps, ~100 yards and strike a tank:

[publius]