Re: [CAD_CAM_EDM_DRO] Stepper motor questions

In a message dated 1/3/2003 10:29:59 AM Central Standard Time,
jerry@... writes:

> My question is this, what is the diffrence between a 4,5,6,8 wire
> motors? I would asume that each pair of wire would make up a coil
> loop inside the motor. And the 4 wire motors have two loops.
> and the 8 wire would have 4 loops that you would take the opposing
> coil and hook up in reverse to the controler. But I'm am confussed
> with 6 wire motors how would you hook these up to a 4 connector board?
> If some one could explain the differnce between 4,6,8 wire motors and
> how to hook them up to a 4 and 6 connector board it would add to my
> understanding.....
>

Jerry: Surely, someone else "in here" has answered this question already,
and most-likely BETTER than I possibly can, but I will try to answer you,
anyway:

A "4 wire" motor is, as you guess, two windings, two ends, each. Those are
always "bipolar". That is, the DC flows throw both windings, then the
polarity of ONE is swapped, making a step. Then, the polarity of the OTHER
winding is swapped, making another step. The DIRECTION of rotation is simply
dependent upon which coil swaps "next".

A "6 wire" motor is normally connected as "unipolar". There are two
windings, but both are "center-tapped". These center-taps are generally
connected via current-limiting resistors (large, energy-wasteful
high-wattage, low-R things) to DC+. Then, the ends of each winding are
connected to DC(-) via NPN transistors, but only ONE "end transistor" is
turned ON at a time, for each winding. If one transistor goes OFF and the
other "end transistor" on that same winding is turned ON, same instant, the
motor steps, and likewise for the other winding. Hard to explain without a
diagram and "face-to-face". HOPEfully you get the picture. Oh: Here, "half
the copper" is never conducting!

An "8 wire" motor has four windings. You can connect these in PARALLEL to
make two windings ("4 wire"), or in SERIES, to make a "6-wire", or, if you
insulate and ignore the (center-tap-) splice, then it's a higher-impedance
4-wire.

Efficiency-wise, the recent 4-wire bipolar are the best, all else being
equal.

But the "bipolar-chopper drives" are electronically MUCH more complex than
the older "unipolar L/R drives" which even I can make "at home". the bipolar
are best built by wizards, and PURCHASED from them! Nicer stuff, too!

HTH! Jan Rowland, Troll.


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