SACG

psycix · Posted: 05/13/2008 6:23 AM Post subject:

SACG - Somewhat Advanced Combustion Gun

This is my first combustion cannon I built. Nothing really special, just a bunch of advanced ghettoness.
Its about one year old now though it started off as a spray and pray and ended with the following specs:

-Chamber: 110 mm diameter, about 27,5 cm long, 2600cm^3 volume.
-Barrel: 50mm barrel, ID about 43mm, perfect for golfballs. Length: 145cm, 2100cm^3 volume.
C:B ratio: about 1.2
-92mm chamber fan
-Dual spark gap, "multisparking" piezo ignition.
-Butane metering

Stuff about it:
-The metering system is quite crappy, due to the fact I couldnt find propane around, I went with butane, wich has way too low vapor pressures. The pressure from the tank differs all the time, and on top of that I couldnt find any adapter for it and had to go with some sort of crappy pressure relief valve wich further reduces pressure. But after I hammered a long nail into it and covered the hole with solder, it worked. When the pressure is too low, I just inject another shot and it became a "inject, guess and pray".
-The fan system is a 9V battery ducttaped to the chamber and to turn it on I just attach the wires to the bolts wich connect to the fan inside.
-The ignition system is a rare form of piezo sparker. On a small spark gap as it is intended to be, it gives about 10-20 sparks on both pressing and releasing the ingnitor. When enlarging the spark gap it does less sparks.
On the current setup it sparks 2 or 3 times on both the press-in and the out.
Ofcourse I only need one spark so its quite useless but its a weird thing.

When was a spray and pray and I shot onto my barn door a few times. The potatoes splattered, no damage to barn.
Then, some other day, I added the chamber fan and used the second spark gap.
I shot onto a wooden board that was in front of my barn door.
The potato went TROUGH the board and then TROUGH the barn door!
Ehmmm... dad? I got something to tell you...
I was afraid that this would be the end of my so far shortlived spudding carreer because my parents wouldnt allow any more guns.
But my dad wasnt angry, he even wanted me to fire it again because at first he didnt believe that the potato when trouough both the board and the door. He was quite impressed, and fixed the door.
And that was just a potato, now imagine a golfball, or worse...

Pictures: