>> I have a couple of stepper motors from an old 5.25" Motors work fine,
>> but I do need more torque, so I am considering building new
>> drivers (using e.g 1207).
>
>  IMHO floppy drives use unipolar 4 phase driving. A scheme that
>uses 1/2 of each coil at a time. Alternating the side that is
>driven alternates the effective magnetic polarity of the coil.
>One way to almost double the low speed torque is to drive both sides
>of each coil simultaneously with a PIC and bipolar driver using twice
>the motors rated voltage because the coils are in series.

I could be wrong, but didn't the original poster say he his motor had 5
leads? This would suggest an internal star connection, with 1 common lead
and 4 leads for the other ends of each coil. If I understand this correctly,
this would make it impossible to use in a bipolar mode.

It might be possible to carefully open the case and see if the internal
star connection can be opened, making each winding completely independent.

Comments? Corrections?

Michael Shiloh