Is it Possible to get over 90% efficiency from a servo motor

[Fizzics]

...If so what would the highest figure be whilst running a 1kw (single or 3 phase) motor under normal conditions also would using a 10:1 Gearbox change that efficiency level?

 

[Hesch]

Yes, it is possible: Use a 3 phase synchronous motor with sinusoidal commutation, and control cos φ carefully. Cos φ shall not be exactly 1.0, but close to. The value depends on the motor.

You must use a digital voltage controller, that reads the angular position of the rotor by means of an encoder.

Of course a gearbox will change the efficiency: No gearbox has an efficiency = 100%

 

[Nidum]

The efficiency of most types of servo motors actually used for servo positioning and similar applications is often quite low .