Out of the box, HG P402 crawler comes with 2-speed gearbox, free channel on receiver and transmitter, but without installed servo.
I've installed plain micro servo. Gearbox is controlled using lever switch on transmitter. Lever acts as a three position switch with dents, but actually it is a potentiometer that allow for analogue control, and thus can be used for other purposes if you do not need 2-speed control.
There is an "idle" position between 1st and 2nd gear. Due to my setup, it can be only reached from one direction.
