Re: [CAD_CAM_EDM_DRO] Stepper vs Servo

I did MY first home-brew "CNC" machine twenty years back, before "Internet"
was a gleam in [anygeek's] eye, and I THINK I can sorta-almost-nearly answer
some of your questions:

In a message dated 7/14/2004 10:56:29 PM Central Standard Time,
jhlebasko@... writes:
1. why does everyone use steppers?<<
You DO mean "more than servos, it would seem"? Because the open-loop concept
is simple, and many of us who were shot down by Differential Equations can
handle that, whereas closed-loop ("servo/encoder" for those of you in Rio Linda)
is simply TOO [deleted] complex for those of us who can barely read. But now
with Mariss' Gecko Servo-Drives, I suppose some of that will slowly change.
2. Isn't closed loop system required to have good control of the tool?<<
Required? By what governmental body? No. A creative home-hacker can
control things QUITE well with steppers, provided he/she does things very carefully,
as would a professional. With my first CNC lathe (pre-PC, controlled by a
PET!), I had 5 tenths movement per-step, and used it only for turning
musical-instrument parts. Was WAY finer "control" than required! Bridgeport vertical
mills with CNC "from the factory"used JUST steppers (=open-loop) for years,
and the results were excellent. I never operated a BP CNC, but I understand
they NOW use servos/encoders, but that is "gossip", I think, which I have never
confirmed.
It appears that most of the software that is within reach supports stepper
motors (step and direction) is the reason for steppers?<<
Is that true? You see, I never "bought" any CNC software. I write my OWN,
using GWBASIC. I didn't even know what "G-M code" WAS until I began to read
bits of that here on the Internet.

It seems logical that most "home-brew-useable software" WOULD, therefore, be
for stepper/open-loop, but I imagine now, some of it will be showing up for
servo/encoder. ONE problem with that I can imagine is that the numbers of
permutations possible with fractional-inch, decimal-inch, metric screw-pitch, and
encoders with powers of ten or binary powers numbers of "clicks" per revolution
would make writing "marketable to home-brewers" software for closed-loop a
nightmare! Not only to write, but to USE, set-up, debug, etc.

Lotsa luck! Jan Rowland


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