Question about trim motor speed
A couple of posters have mentioned both direction and speed as inputs to the trim motor. Is the motor speed really variable (I doubt it), or does the motor run at constant speed when activated (my bet)? If electric trim in the 737 is a variable speed system, then there must be another microprocessor or software routine somewhere that computes the PWM (pulse width modulation) pulse train.
YYZjim
Not sure how it is accomplished, whether variable voltage via resistors or software processing or something, but the trim does indeed function at 2 different speeds. Flaps up: both manual electric and autopilot trim at a "slow" speed
Flaps down: both manual electric and autopilot trim at a "fast" speed.
By all reports the MCAS trims at the fast speed even when flaps are up (using the autopilot trim function and the STS system) while the pilot trims back to neutral (in a failure mode scenario) at the slow speed.