Some new toys in the house. First is a pair of mini RC helicopters from ThinkGeek. The helicopters charge from the radio (well, IR really) control box, good for about 10 mins of flying per charge. I think I'll buy one of those slabs of batteries from Bunnings. I won't get a chance to fly them until I'm back from holiday, late next week.
The other toy is not quite working yet. It is a gas cannon, otherwise known as a spud gun. The idea is that a projectile is inserted in the barrel, then a cap is removed at the rear; squirt in aerosol propellant (hairspray is good, apparently), close cap, press barbecue igniter. Bang! Projectile exits barrel.
The Mk 1 cannon. Note the nifty handle on the barrel, and the double-cavity fuel chamber. The piece of dowel is the ramrod. The projectile is a wadded up piece of cloth, to start with.
So far I've managed to ignite the evaporating fumes from the PVC cement that I used to glue it together, but my spray cans don't do the trick. We definitely have a spark, but so far we haven't had an explosion. I think the right fuel will be the answer.
The business end. If I was doing it again, I'd put the screw cap in line with the main barrel, so I could check if the barrel is clear and also push stuck projectiles back up the barrel. The igniter could go in the flat end cap of the side branch, so it wouldn't block the main chamber and barrel. That will be in the Mk 2 design. Or maybe something like this.