If no motor data is available I suspect you could just give it a try. Most
industrial steppers I work with get quite warm (80 deg celsius or so) at max
torque and speed and I know the steppers in diskdrives do not.

There are (at least) these things to consider:
-Increasing the current thru the windings might not increase the magnetic
field due to saturation of the core (not likely but needs to be mentioned)
-Is the rotor a permanent magnet? if so you might demagnetise it with a too
high current.
-The max current (thus torque) could be limited by the current being the
maximum current for the winding diameter (most likely cause in small
steppers like these)
-The max current could be limited by winding heating max power /cubic mm
...a high motor temp would be an indication for this

As paul webster already suggests in his message if the ratio run/stopped is
low enough you could benefit from a reduced current when stopped and a
boosted current when running.

Peter

-----Original Message-----
From: Paul B. Webster VK2BZC <paulb@MIDCOAST.COM.AU>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Sunday, May 23, 1999 9:39 AM
Subject: Re: [OT] stepper motor data..


>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.