RE: [CAD_CAM_EDM_DRO] Re: COMPLETE 3 axis CNC electronics package (plug-n-cut, ready to go)

Hi Alan,

If you have a six wire stepper then it can be configured as LR with power
going into the centre tap and one phase being one side of the winding and
the other phase being the opposite side. This allows the stepping without
the use of an H-Bridge to reverse the current flow in the winding; just
single NPN transistors. Cheap!

When such a stepper is used with an H-Bridge you get the same torque when
you use only one half of the winding. Centre tap to one end. You get more
torque if you ignore the centre tap and use the outer two connections
because now your AMP * TURNS is doubled but your inductance also goes up so
your maximum step rate is decreased -- all other things being equal.

An 8 wire motor has all the advantages. Putting the windings in series or
putting the windings in parallel or using them in six wire mode or using
just two windings total. In parallel, inductance is halved but AMP TURNS is
not doubled.

John Dammeyer

> Hi ballendo,
>
> Glad you liked the post.
>
> I haven't seen double ratings for steppers. If the same amount of
> winding is driven with the same current, then one would
> expect the same
> torque.
>
> True, Bipolar drivers are more efficient, and simpler to
> wire! I prefer
> bipolar drives, probably because they were the first high speed, high
> power drivers I worked with. After suffering with old (70's) design
> unipolar drivers, they were a welcome relief.
>
> The technology has come a long way.
>
> Alan KM6VV
>
>
> ballendo wrote:
> > Alan,
> >
> > Nice post.
> >
> > But it's only fair to mention that Bipolar DOES still have a couple
> > advantages over Unipolar; even when both are chopper style drives.
> >
> > A bipolar drive will provide more torque to a given motor than
> > unipolar. This is why we see the "same" size 23 double
> stack 3amp, 1
> > ohm motor nowadays labeled with either 280 oz.in. (bipolar) or 200
> > oz.in. (unipolar).
> >
> > It's also true that bipolar drivers are more efficient with respect
> > to the input power required. This is due to their ability to
> > recirculate "unused" power back into the supply.
> >
> > Finally, the bipolar drive requires fewer wires, so too fewer
> > connections to pay for or go bad.
> >
> > Now, against that is the de facto truth that for a given PRICE, you
> > can get a chopper unipolar drive with higher power supply
> > capability, and higher motor amperage capability.
> >
> > So IMO it all pretty much averages out; both are good choices.
> >
> > <SNIP>
> > Ballendo
> >
>
>
>
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