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Why do they call RC motors servos? Answered

If they were true servos there would be a feedback signal generated. What is the proper term for these motors, maybe a stepper?


"Servo" is an abbreviation for servomechanism. It is a device used to control another mechanism.

IME, RC "servo motors" were originally regular motors (whether handmade or prebuilt) that used a return spring to draw the armature back to some preset "zero". The width of pulses sent to drive the motor resulted in a proportional force being delivered against the spring force, allowing control of rudders, throttles, etc. by deflecting the armature a given angle corresponding to the pulse width and duty cycle of said control signal.

I don't know whether the current servos used for RC control are actually steppers (a special class of motor that uses discrete pulses to deflect the armature a specific number of degrees per pulse) or not, but as long as they fulfill the mission of a servo motor they are then...servos.

THey are DC motors, with gear boxes and feedback pots. They are position servos. They are now controlled by a PWM train fed to them from the receiver, with a 50Hz PRF and a 20-50usec duty cycle.

yeah, I wasn't sure. I haven't played with RC servos in years and years. My most current experience is with hydraulic and electrohydraulic servos

The feedback is entirely internal. The device moves, if it can, to the position specified by its input signal. If there is a disturbance, the servo moves to restore itself to the position specified by the input.


A feed back signal is generated and used by the circuit inside the servo.

and some servos deliver pot-feedback to the controller such that it can be aware of the exact location of the armature.

Servo is the masculine form of "servant" in Italian. Is that why electrical servomechanisms are called servos? I dunno.

As said, also a servo system in general is designed to follow an input so it moves as much as the input demands. There were RC systems called Bang Bang that just went all left/all right/centre for very simple control.