Servos are the end units in a radio control chain.
They are used to move the aircraft's control surfaces, the motor throttle and
to actuate other devices such as retractable landing gears.
A servo consists basically in a motor, gearbox, feedback
potentiometer and an electronic board inside a plastic case.
Outside are the servo arm and the servo cable and plug.
The servo arm is often a plastic piece with holes on it
for attaching push rods or other mechanical linkages.
There are linear and rotary servos, but the most widespread today are the rotary
servos whose arm rotates about 45 degrees left and right from its centre point.
The picture on right shows some servo
hardware, such as mounting screws,
rubber pads, and different sorts of
servo arms.
