Variable reluctance motor drive?

Hi group-

I've been experimenting with variable stepper motor samples for personal
education. One of my motor samples is what I'm pretty sure is a variable
reluctance motor (VRM) salvaged from an old PC tape drive. It has three
windings each connected at one end with a common high side connection. From
my reading of how to drive a VRM, it appears it's driven just like a stepper
motor: energizing one winding at a time in succession. Basically, I'm
following the method found at
http://www.cs.uiowa.edu/~jones/step/types.html.

I have an on/off stepper driver (three switches) which I can switch a
constant current on and off (200 mA) under microcontroller control. I just
can't seem to get this VRM to turn reliably. It steps but often steps
backwards and it has a weak holding torque. I'm having my doubts that I'm
drving it properly. I'm starting to think that driving a VRM is much more
complicated than the above web site suggests.

I've searched the web for relevent information about VRMs and I can't find
anything that goes into any great detail. It's either not covered to my
satisfaction on the web or I'm doing something completely wrong.

Can anyone please point me to a resource that I can use that will help me
uderstand the drive requirements of a VRM?

Thanks, JJS


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