Overhead fan turning backwards.

Originally posted by JS357
I think CD players have brushless DC direct drive motors. Air factors should be consistent and minor. I tried it with a CD on two of my players that have an openable door, which upon opening, turns off the motor. One of them, a Kloss 88CD, displayed no reverse motion after coming to rest. The other, a Sony Discman, displayed a slight pause and then a definite ...[text shortened]... re direct drive, too, so that could be tried. Reportedly, PC fans are too. (Wikipedia)

Interesting thought. If you had a sensitive force probe, you could theoretically measure the amount of force it would take to manually turn the disc or blade, there should be places where the force needed would be greater, more torque needed at certain spots around the circle of motion. I know what that force feels like in servo motors, they are designed to have a stepping motion of X amount of movement per torque pulse.

You can feel the force holding it in one position and by manually turning the shaft you can feel the force you overcome to get to the next position. I am trying to remember if you feel a residual effect when it is powered down. I don't have a stepper motor in hand right now to see.