Re: 8-wire 1/2coil stepper?

At 17:14 08/05/2002 +0000, you wrote:

>Bipolar 1/2 coil vs bipolar parallel or bipolar series is not the same as
>unipolar rating. You are correct that there is about a 30% greater torque
>when using a biploar driver vs a unipolar driver. But, there is only a few %
>difference between the various bipolar connections.

Correct me if I'm wrong, but I believe that if you are only using 2 coils
of an 8-wire motor, you should be using the unipolar current rating, and
will get broadly the same performance as you would with a unipolar drive
(assuming the same supply voltage in both cases). The 30% advantage with
bipolar drive is a consequence of being able to parallel connect the coils
& uprate the (unipolar) current by 1.41 (or series connect coils & downrate
the current by 1/1.41). I quote from Marris's post back in January (message
36945):

"If an 8-wire motor has a 1A unipolar rating and you have a full step or
half step drive, then:

Use 1A if you are running the motor with a unipolar drive (6 wire)

Use 1A if you are running half-winding bipolar

Use 1.41A if you are running parallel bipolar

Use 0.707A if you are running series bipolar

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<The rest snipped>
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"

Regards,
Tony

>Tim
>[Denver, CO]
>
>-----Original Message-----
>
> >Its not necessarily just 3% difference - it depends greatly on the motor
> >spec. For example, take a look at:
> >
> >http://www.mae.it/us/2231.htm
> >
> >This 8-wire motor (RH column of the table) is quoted as giving 30% more
> >holding torque when bipolar parallel connected vs. unipolar connected. They
> >uprate the current by a factor of 1.4 for bipolar parallel connection (or
> >downrate by 1/1.4 for series connection).