What is the purpose of the shallow channel (indent) on the side of the wooden body?
The shallow channel is to provide the alignment for the two motors as they are being epoxied to the wood block. It increases the epoxy contact surface to the motors (and thus the strength of the bond), and allows the use of a strong rubber band across both motors to hold the motors in position as the epoxy cures. In this way the motor axles are pointing in the exact direction they need to be for alignment with the end holes of the white plastic L-pieces (Custom lever arm and pivot, item #3).
