The ability to change the pitch in flight is as significant for the airplane pilot as for the driver of a car to shift gears in the transmission. This results in substantial savings in fuel, engine wear and noise.
Pilot controls the pitch through the toggle switch mounted in the cockpit.
Pressing the toggle switch one way sends electric current through the graphite brushes to the slip rings and finally to the electric motor. Depressing the toggle switch the other way-reverses the polarity of the current and the rotation of the electric motor. The pitch change operation is similar to the power windows in an automobile. As long as you hold the switch in one direction the pitch changes in that direction and you observe the result on your RPM meter. Torque from the electric motor is multiplied in a planetary gear drive which turns the lead screw.