> >> I built a desktop milling machine a couple of years ago.  It used
> >> 5v rated steppers, so I hooked them up to 5volts.  I got no torque
> >> out of them at all.
> >
> > That would be correct.
> >
> Really?  Is that generally true of steppers, or only for certain
> classes?

It is common to run steppers from a higher than rated-voltage voltage source
with series resistors such that the stepper has rated voltage across it when
the current stabilises. The L/R time constant is thus reduced. This is
effectively driving from an approximation to a  current source. The same
result can be achieved electronically by implementing an active current
source. This MAY allow somewhat lower driving voltage than with the
resistive only version for the same result as the coil can be initially run
closer to "full-throttle" until the current ramps to rated value and is then
held at this value.


        RM

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