What is OPTO?

Opto in radio control (RC) contexts means Opto-coupler. On the ESC (Electronic Speed Controller) ie. Motor Controller, the power used to drive the motor is electrically isolated from the power used to control the servos. This is supposed to reduce radio interference between the motor and receiver as light signals are used between the motor and receiver circuits. As a result, the ESC requires separate battery packs, one of the motor and the other for the receiver and servos.