Re: Variable reluctance motor drive?

On Jul 30, 8:36 am, "John Speth" <johnsp...@xxxxxxxxx> wrote:
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 athttp://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


Hi
There are two types of steppers. One type has a permanent magnet the
other
does not.
This means that one will hold with no power applied while the other
will not.
For the type that has no magnet, turning the power off to a winding
before
it is safely centered on that pole will cause it to start up in an
erratic direction.
Does this sound like the problem your having?
The other thing is that you have to ramp the stepping rate and avoid
staying in the resonant region for that system when changing step
rates.
Dwight
.