I wanted to build something destructive so here it is.
The cannon is activated by placing a redstone block on the far left piston(which dispenses the propellant) and then removing it (which dispenses the projectiles)
By removing the block later you delay the projectiles (and by removing the redstone block a bit quicker you kinda get a airburst scattershot cannon)
The same kind of princeple with the fire charge dispensers(you place a redstone block to switch to auto fire(semi auto by moving the machine))
And at last you just place torches on the engine(indicated with a red circle) to move the machine.
by ZookeepergameOk3493