Servos – Analog vs. Digital
Analog servos require a PWM pulse that occurs within a window of allowable
refresh range. Every time an analog servo receives the PWM pulse, the
servo driver increases the drive power to the servo motor for a few
milliseconds, and then a ramps down the power. Without the PWM refresh
the driver never outputs current to the motor and the servo's holding force
goes away completely.
A digital servo updates the motor driver independently from the frame rate.
Some servos, such as those used for tail rotors in helicopters update the
motor driver every 3ms (333 times per second), even though the frame rate
may only be 22ms. Most digital servos can handle frames rates as fast as
5ms.
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