You need torque arms. Otherwise the motor's axle will rip out the the dropouts from your bike.

The wrench is a crescent wrench that goes on the right nut. Because of the direction of the force of the motor, the axle on the right side has an urge to turn counterclockwise, this in effect causes the right nut to tighten. If the nut is held stationary, it will prevent the axle from twisting, thereby preventing the axle from ripping out the dropout. However, I do not know how strong this is. Btw, you attach the wrench with pipe clamps.