The whole tank is completely controlled with only 4 servos. One to operate the turret elevation, one modified servo for the turret rotation (rotates continuously) and two for the speed controllers. The two speed controllers in the tank are the drill trigger speed controllers which I modified to be operated with servos. I took out the stiff coil spring in the trigger speed controllers and designed a cam mechanism which engages forward and reverse. All cordless drills have this forward and reverse switch, all it does is reverse the direction in which the current flows. And that is about it, I only use 4 channels, and the receiver and battery pack is housed in the turret for easy access. The two servo cables coming from the two speed controllers just go through the center shaft of the turret to the receiver.