We used a 14-cell, 16.8v Ni-Cd battery. Its rated for 10Ah, but it fully discharges in about a week... making it less useful. Whatever though, you can put a useful charge into it in less than an hour.
The following image shows the completed box. The small switch controls a chamber fan, and the large switch is connected to the igniter coil (it won the "most satisfying click" contest). A handle serves as both a switch guard and an easy way to move the box, which weighs about 10 pounds.
There is direct access to the terminals for charging
The insides are quite simple, a switch for the fan, a switch for the coil, one common wire.
An extra piece of nichrome wire
So this is the back end of the cannon. Yes, the design is messed up. The propane still isnt metered. We just spray it in the end of the hose. I guess a meter is the next project. The screws for the igniter coil used to be a "spark gap". Also you can see my power supply, which can power the cannon, charge the battery, or both
.
No math was done in the construction of this cannon. The barrel is just the 6 foot piece that we originally bought. The chamber is like 2.5 feet. :dontknow:
Inside the bottom half
With the igniter turned on
. Sure ebay or what have you, But this cost us $0 and the cannon takes like 2 minutes to reload anyways. Its not like we are going to be chasing deer with it.
