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Servo

A motor-driven device for moving control surfaces and throttle of a radio controlled aeroplane.

The servo output arm is the removable arm or wheel which bolts to the output shaft of a servo and connects to the pushrod. These are often cut and modified to suit the paricular application. Careful positioning of the holes in the output arms will allow you to produce a mechanical differential effect for airlerons or even throttle control where more precision is required around the idle setting.

Servo reversing is a radio feature that allows you to install the servos where they can give the best pushrod routing without concern about the direction of servo rotation. When your installation is complete, turn on your radio and check each channel. If a channel operates opposite of its intended direction, a simple flick of a switch corrects the problem.

Servos are best mounted as square to the control surfaces as possible. Use gromments and the copper furrells provided with servos. Best mounted on parallel spruce mounts as servos might have a torque rating of 1.5 kgs and higher so mounting needs to be good to take on loads imposed. Try and keep the pushrods as straight as possible as this gives the most efficient use of the power from the servo to the control surface.

Keeping the control linkage as short as possible will reduce the amount of loss in control due to flexing in the control link. In this case the servo is mounted in the tail section of the aircraft, this has the negative effect of being in the wrong place with regards to centre of gravity and can result in more weight being needed in the nose of the aircraft to balance. However, the positive side is that the control is very direct.

See also: Differential Control.