Re: [CAD_CAM_EDM_DRO] Xylotex or Gecko step driver for my Mill/Drill?

in answer to you question

Thanks for the clear explanation there. Now, I have another question: Is
it feasible to use a motor with six wires (that an ohmmeter shows me as
being
wired for unipolar operation) as a bipolar motor by simply ignoring the
center taps? I'm wondering about the phasing of the two half coils there...

Yes. But you have to assume half the amps per phase (apparantly) so a 2amp
unipolar can run at 1amp bipolar.
Im no expert but thats what it says in my Xylotec pdf.

Nick

----- Original Message -----
From: "Roy J. Tellason" <rtellason@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, May 18, 2004 3:37 AM
Subject: Re: [CAD_CAM_EDM_DRO] Xylotex or Gecko step driver for my
Mill/Drill?


> On Sunday 16 May 2004 12:08 pm, Jon Elson wrote:
> > Roy J. Tellason wrote:
> > >On Saturday 15 May 2004 11:05 pm, Jon Elson wrote:
> > >>>but I ruled that one out because it's a unipolar only board.
> > >>
> > >>Good move, as most unipolar drives are very poor performers at higher
> > >>speeds
> > >
> > >Why is that?
> > >
> > >Would it have something to do with a bipolar setup energizing coils in
the
> > >reverse direction rather than just turning them off?
>
> > Yup, that is basically the problem. With the typical unipolar drive,
> > the power source is connected to the center tap, and transistors ground
one
> > end or the other of the winding. When you ground one end, there is
still
> > circulating current in the other half, fighting the field you are trying
to
> > build in the newly powered winding. This energy has to go somewhere,
and
> > it ends up being burned off in some diode-resistor arrangement. It is a
> > hard topology to harvest this energy constructively. If there is no
> > resistor, the current in the shut-off winding dies very slowly. If
there
> > is a resistor, then it gets quite hot at high step rates.
> >
> > With a bipolar drive, the power source is applied across the whole
winding,
> > and is reversed to reverse the field. The field already in the winding
> > opposes the power source at the moment the transistors are switched,
> > and the reversed voltage across the winding collapses the existing field
> > and quickly builds it again in the opposite direction. The energy
mostly
> > ends up back in the power supply, so there are no big resistors to burn
> > off the left-over field.
> >
> > There are ways around this, but they are generally more complicated than
> > the bipolar drive scheme. The only advantage to unipolar is it saves a
> > 4 transistors per motor.
>
> Thanks for the clear explanation there. Now, I have another question:
Is
> it feasible to use a motor with six wires (that an ohmmeter shows me as
being
> wired for unipolar operation) as a bipolar motor by simply ignoring the
> center taps? I'm wondering about the phasing of the two half coils
there...
>
>
>
>
>
>
>
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