Janusz J. Mlodzianowski wrote:

> I have a couple of stepper motors disassembled from old 5.25"
> 360kB TEAC FDDs (FD-55BR-528-U). Motors work fine, but I do need more
> torque, so I am considering building new drivers (using e.g 1207).
> I would like to know more about motors.

  Mmmm.  I suppose http://www.doc.ic.ac.uk/~ih/doc/stepper/ doesn't help
so much as it is a different brand.  Motors in general, you will find
http://www.cs.uiowa.edu/~jones/step/index.html a good summary.

> The motor is driven via M54534P transistor array.  Can I increase
> torque by driving more current (how high),

  Frankly, I suspect the original would have been designed for near
maximum torque.  There is a limit on the current to which you can safely
subject the windings for one thing.  You may use conservation techniques
to limit idling current, but your concern for torque hints you may want
more than intermittent use.

> what is the winding sequence?

  Try this.  You know the brown is common.  Connect a speaker between
this and one other wire, then "flick" a single (1.5V) cell between the
brown and each of the other three.  The one which gives a healthy click
is the other side of the same winding.  Do the test with the other two
wires to confirm.

  I feel it to be rather silly to separate these motors from the drive
electronics, at least the part which is designed, presumably optimally,
to drive them.  Unless perhaps, you are concerned about size.

  In addition, it gives you a very versatile interface.
--
  Cheers,
        Paul B.