"Lord Garth" wrote in message
t...
This motor apparently has 3 coils with one end common to
all three. The motor came from a Western Digital drive. Does
anybody know the pulse pattern to the coils?

Nidec will never reveal nothing.

Is it a 4 lead or 3?

If 4 lead, look up 3 phase unipolar drive.
If 3 lead, look up 3 phase bipolar drive. This is the most common and is
driven by three push-pull outputs. It probably does not have any hall effect
sensors. Spindle motors are often started like a setp motor in a forced
commutation sequence and then above a certain speed, rely on the back-emf
sensing of the off coil to give velocity feedback for speed control. In the
commutation sequence, one of the three coils is always off and is used for
bemf sensing.

Lots of motor manufacturers have phase sequence charts for these types of
motors. There are plenty of drive and IC manufacturers with appnotes on the
subject. google for "sensorless bldc"

Hope that helps
Oppie