I've wanted to have a working (ie, noisemaking) cannon, partly to bring to pirate events and partly because it's cool. Because we'll be firing this off at very public events, it was important that it be very safe in all aspects. So black powder was completely out (besides the expense of an all brass or all iron cannon) due to the extreme hazard of gunpowder and the large quantities of smoke produced, and other flammable fuels such as butane, lighter fluid, hairspray, etc. might be frowned on by event co-ordinators and are dangerous in and of themselves. Air power was out because a thumping compressor will detract from the illusion and requires constant power.

Brian of the Beer Bard Privateers turned me on to calcium carbide cannons. I'd had a miner's lamp when I was a kid that used big chunks of calcium carbide, but hadn't thought about it in a long time. Turns out someone back in the early 20th Century (1917?) designed a "safe" cannon using calcium carbide.

CC by itself is a rock that you can't burn even if you put a torch to it. In the presence of water, it decomposes to lime and acetylene gas. For the cannon, the CC is crushed into something about like tablesalt grains.

It comes in a tube called Bangsite. I bought several tubes and a special hopper that feeds a measured amount of Bangsite from http://www.cannon-mania.com

Brian's cannon is made from ABS, the acetylene burns so quickly that there is little residual heat. I think it was 2 inch ABS.

So mine is also made from ABS. The combustion chamber must have a constriction. In Brian's 2 inch diameter ABS cannon, the constriction was from a 1 inch dowel passed through the barrel, this was also how it was attached to the base. Brian's is charged with CC and touched off via a small hole where the touch-hole would be on a powder cannon.

However, I found that it would spite lime water back in my face when fired, and I suspect some misfires were caused by wind blowing the acetylene out of the touch hole. So I determined to do things a little differently by using a BBQ piezo ignitor and some other way to put in a charge of CC.

And bigger is better, right? So I also decided on a larger firing chamber. Bwah ha ha hah hahh!!!!

A 3" threaded coupling with threaded cap, attached to a 3" to 2" reducer (for the constriction) by a chunk of 3" ABS just long enough so the ends of the reducer and the coupling just butt together. Then a long piece of 2" ABS for a barrel. I cut a few different lengths to compare the sound.

The BBQ igniter is installed with a 1/2 inch PVC Union. That is a 3 piece fitting, one end is epoxied into a hole I drilled into the square end of the threaded cap. The other end has the igniter epoxied into it. The threaded cap can be quickly removed to blow out between shots.

For the tight fitting pipe to coupling/union, I used ABS cement. For less perfect joins (metal to ABS, PVC union to drilled hole) I used plastic epoxy. Much better than regular epoxies, as it contains a solvent to really bite into the plastic.

I got the ABS, PVC union, and BBQ Piezo Ignitor at Ace Hardware.

Representative pictures:

Threaded cap:
http://tinyurl.com/2uum2k

Threaded coupling:
http://tinyurl.com/34pqd3

3 to 2 inch reducing coupling:
http://tinyurl.com/33fy2z

The PVC union:
http://tinyurl.com/2ll9rq

I bought the Cannon Charger from Cannon-Mania.com. Dispenses a nice measured amount of calcium carbide. Got a few tubes of the carbide powder, too.
http://www.cannon-mania.com/images/bigbang-parts/cc-charger.jpg

I used ABS cement to glue the 2 to 3 inch adapter to the 3 inch threaded coupling adapter with a short chunk of 3 inch ABS.

I drilled out the square end of the threaded plug to fit the end of the 1.5 inch PVC coupling and used Plastic Epoxy to glue it in.

The other end of the PVC coupling got cut down short, so that the BBQ ignitor would fit far enough into the firing chamber.

Short piece of 16 guage solid copper wire soldered to the ground on the ignitor, bent to make a spark gap with the business end of the ignitor.

Ignitor expoxied into the PVC coupling. Now I can quickly remove the ignitor to shake the water off, and blow the firing chamber out between shots.

Drilled a 1" hole into the "top" of the firing chamber and dremelled the top flat to fit the carbide feeder from Cannon-Mania.com and epoxied it in.

Let everything sit for more than 24 hours after the last thing was glued in.

Cut out a few barrels. Two that are 2" by 14" and 28", the other is 4" by 24" and fits over the outside. Press fit only since I'm not going to shoot any objects.

I made a video of some of the tests, I'll be posting it to YouTube.

I remove the ignitor to add water. Pour some water in, tilt cannon back to about 45 degrees and let excess water run out of ignitor hole. Reinstall ignitor.

Found out that the size of my firing chamber is larger than what the carbide feeder is designed for. One charge, wait a slow count of 10 and fire, gives out a cute little "choot!" Not very impressive.

Two charges of carbide, wait a slow count of 10.... Bam! Quite loud.

Install the 2 x 14 inch barrel, BAM! Wow! Very loud. And reviewing the video, about 8 inches of pale flame for one frame.

With the 2 x 28 and 4 x 24 inch barrels, may be a bit louder but mostly it's a deeper tone, as expected. One of the neighbors had come out to see what was going on, she said that she could see flame shoot out the end of the barrel. Inside of the barrel was not detectably (by my hand) warmer than it had been before the shot.

Important to wait the full count of 10 before firing to allow all the acetylene to be generated before firing. I removed the ignitor, shook it off, and blew out the chamber between every shot. A little water on the ignitor didn't seem to have any ill effects, there were no misfires. Following those directions and using 2 charges of carbide, -every- shot was loud!

Since it's loud with any of the barrels, my main criteria in choosing which barrel to use will be based on making it look as much like a real cannon as possible. I still need to build a good looking carriage for it.

I am not entirely happy with the placement of the ignitor. I didn't place it on the side/top of the barrel as it is fairly long and I didn't want it sticking up. On the end it blends in, but the barrel cannot be tipped back very far or water floods the ignitor. I can't simply mount it offset on the end cap, because it screws in further as the threads wear so the ignitor will end up under water at some point.

I could mount it along the combustion chamber along the top as Yurtle Turtle has his mounted, but it is not then easily removeable to clear the water and blow out the chamber.

Perhaps the solution is to copy one aspect of Brian's cannon. He uses a threaded T connector for the combustion chamber, so that one end of the T is at the bottom and acts as a reservoir for the water. This would keep the water further from my ignitor. I would then drill and mount the CC reservoir so that it is directly above that water reservoir when the cannon is mounted at an angle of about 30 degrees.

Since Brian's site seems to be down right now, here is a description of his cannon to my recollection:

2 inch ABS pipe. Combustion chamber is a "T", with threaded plugs in two of the openings and a 2 inch barrel. A coupling on the end of the barrel just so it looks more cannon-like. Hole drilled across about 1/4 of the way from the back end to fit about a 1 inch dowel. That dowel is how it is held in the carriage, and provides the required constriction of the outlet side of the firing chamber. Touch-hole drilled near back end of the cannon. the whole thing about 18 inches long.

A little water poured in, tilt cannon a little forward to let excess run out. Pour in about a teaspoon or two of Bangsite (Calcium Carbide) into touch hole. Wait slow count of ten, set lighter to touch hole. Bang!

When his site is up again, here it is:
http://privateer.omena.org/

For the record, I'm not sure mine is louder than Brian's design.

As always, use your own judgement, I'm not responsible for anything that happens if you build any of this.

Alien Steve