Re: [CAD_CAM_EDM_DRO] Newbie to CNC - 400 step/rev motors

In a message dated 3/13/2003 4:48:55 PM Central Standard Time,
kevinh@... writes:

> From reading the on the
> Xylotex website I see that it can be configured for full, 1/2, 1/4,
> and 1/8 step. Will this alllow me to use motors besides a 200 step?
>

Kevin:

The "industry standard" for stepper-motors is 200 steps/turn. All that means
is, if the two windings are fully-energized, and the DC polarity is reversed
on first ONE winding, then the other, and repeat, after 200 such
polarity-reversals, the motor will have turned ONE revolution. The Oriental
400 step motors are like that, except they require 400 such
polarity-reversals for one full turn. I have a pair of Size-23 Oriental
steppers on my home-brew plotter I use for drawing my home-brew CNC
lathe-programs (before ruining good material, if a goof in a program), and
they ARE "fine", but the problem is they move only HALF the distance, so SOME
"editing detail" is sacrificed.

These things you say you read about 1/2, 1/4, and 1/8 step---and the Gecko
G210, which can do 1/5 and 1/10 step!---are details of the DRIVE for the
motors they are specified to operate. They can "ramp" the winding-currents
in those fractions, so that there are not simply 200 "jumps" of 1.8° per
step, but up to 2000!

Earlier "non-microstep" drives which were "full-" and "half-" step ONLY, were
simple "ON-OFF" switches (solid-state switches, that is!), which simply
switched the DC on or off to either end of two center-tapped coils in the
motors. They could do "HALF-stepping" by first reversing the polarity in ONE
coil, then turning OFF the other. Then, the REVERSE polarity of the second
coil would come on, and next, the FIRST coil would turn off. (Impossible to
visualize without a "chart", or at least, "pencil and paper"!). There was
some loss of torque in those when connected for half-stepping, but changes in
the acceleration-rate requirements, etc. A kind of nightmare for a newbie!

Your best bet, if you are a beginner, is to choose the 200 step motors, and
MY personal opinion is make them BIPOLAR ("4-wire") types, and use the Gecko
G210 drives, which can do 200, 400, 1000, and 2000 steps per turn with "200
step motors". The G201 can ONLY do 2000 steps per turn as I understand
things. There is at least one other drive make I see discussed on this list
which can do those 1/2, 1/4, and 1/8 steps per step, but I forget the
brand-name, as I have not yet tried one. If that drive were used on a 200
step motor, you'd have 400 steps, 800 steps, or 1600 steps per turn. If a
400-step motor (Oriental), DOUBLE those numbers.

As there are "surprises" with this stepper-motor stuff, I suggest you simply
stick to 200 step motors and Gecko or some other good make of drive discussed
on this list, and LEARN all about all that before you go trying to decide
which "numbers of steps and transistors and polarities" to choose! Jan
Rowland


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