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

Hi John,

Bipolar or Unipolar doesn't matter! But before I get flamed, let me explain
that either mode can be CHOPPED. Chopped is what you want! Chopped mode
allows the current in the stepper windings to build up quickly, and then be
cycled on/off to maintain the current at the desired rate until being shut
off for the next step.

Unipolar drives got a bad reputation from the days when they were driven
with L/R drivers (think BIG POWER resistors). These made for slow drives,
and wasted much current. Not so with choppers! Unipolar drivers can
actually be simpler, as only 4 Darlington power transistors or FETs are
needed; vice two H-bridges, each with 4 power devices (simplified
description).

And guess what? The motors are really just about the same, only the NUMBER
of wires brought out for the ends of the windings is different! The old
unipolar scheme often brought out only 5 wires. 4, 6 or 8 wires are
commonly seen now. Modern stepper motors do have a significant improvement,
they use modern magnets and laminated RECTANGULAR cores (although some look
more like hex).

200 step motors have 1.8 degrees per step. Some take it a little further,
400 steps, .9 degrees per step. This is inherent to the stepper it's self,
the number of poles. MICROSTEPPING uses varying currents in the windings
(sin/cos) to effectively give MORE steps. 8 microsteps gives a smoother
step through rotation, and thus lessens the tendency for stepper motors to
stall due to resonances in the slower speeds. Altering the current phase in
relation to the mechanical position also minimizes the resonances. For a
better explanation, see the white papers on the Gecko web site.

Alan KM6VV

>
> 3 amp unipolar chopper driver board,
>
> Okay I am a late bloomer, but Somehow I thought
> Bipolar or microstepping was "better".
> IN a few sentences why would somone want to build a
> unipolar device when the majority or the items I see
> for sale are bipolar etc.
> I have a perfefctly fine bechtop- miling machine that
> I have about given away beacuse it had unipolar motors
> and I coukld not get any responses about the drivers
> etc?
> So what really give with this Bipolar, Unipolar,
> Microstepping, .9 degrees 1.8 degrees.??????????
> John
>