> from the list), hooked everything up and the stepper displays strange
> behavior. Sometimes it will turn 1/2 rev then stop and quiver. I accidentally
> found that if it would only turn if the wire  leads coming out of the motor
> were coiled 180 deg around the motor. When I would hold the shaft and
> depress the button the motor would turn, unwind the leads then stop a quiver.
> If I put the leads straight it the motor will just quiver. I checked the
> connections and 3 other motors that all exhibited this behavior.
>
> I am using a ULN 2803 to drive the stepper. ANy ideas?
>
> The code I used is designed to half step ther stepper.
> www.beowulf.demon.co.uk.
> The stepper I am using is unipolar, two phase, 6 lead, 12v, 15 deg per step
>
>
> My question is, are all motors capable of half stepping?
> What else could be causing this behavior?
> Can I change the lookup table to get full steps?
>
>
The fact that the behaviour alters with wire orientation strongly
suggests hardware problems.
Is the FreeWheel pin on the ULN2803 connected to the motor VCC?
Is there sufficient power supply decoupling?.. try a BIG cap
(10,000uF per AMP) across the motor supply and / or PIC supply.
Coiling the leads around the motor sounds like adding inductance.. a
low pass filter is being created in the wires.Reinforcing my
suggestions of ULN 2803 freewheel pin and big caps.

_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand
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