Before and after paint
Put a 12″ piece of PVC into the top. This is where the marshmallows will be loaded and fired.
You will need to solder wires from the sprinkler valve, switches and extra wire to battery pack. Hide battery in Altoids can.
One switch is your safety, the other is the firing switch.
Load marshmallow. Pump with bike pump to 30 PSI. Flip your safety off and fire. The marshmallows will go far, so make sure you have a safe area to shoot them.
WARNING: Only pump the air cannon to 30PSI. Any more could result in damage to cannon or yourself.