Janusz J. Mlodzianowski wrote:

> 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 eac
h 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. The
more turns of wire you drive the larger is the generated magnetic force. If you
have power supply capacity to waste you can also use
a resistor to ballast the coil and operate it safely at a higher voltage. This w
ill increase the torque at high speed. For more on
this see this URL:
http://www.svskits.com/FreeInfo/Motion/Stpnote.htm
For a Schematic of a 1/2 bridge bipolar driver see this URL.
http://www.svskits.com/FreeInfo/Motion/Halfbrdg.htm
If you are driving only one motor then a full bridge driver would allow the use
of a more cost efficient power supply.

Disclaimer: these are information pages provided by the company I work for. Noth
ing is offered for sale on these pages . . Brian
--------------------------------------------
Brian Whittaker SVSKITS.COM
Voice: 510-582-6602 FAX: 510-291-2218
SVS_KITS@MSN.COM URL: http://www.svskits.com