Re: [CAD_CAM_EDM_DRO] Beginner seeks cheap motor in Uk

In a message dated 26-Jul-01 11:03:11 Central Daylight Time,
mark.taft@... writes:

> NEW ! Servo motors with optical encoders and components for Gecko G320/G340
> amps are now available.
>
> Are these standard 4 phase stepper motors ?
>
> whats a Gecko ?
>

Mark!

This question indicates confusion! A "Servo motor" is a
precision/special-application type of D.C. electric motor. It can be used to
stir drinks with only a battery (oversimplification for illustration, mind
you!). It will run until the current is turned off, and will then "coast" to
whatever point the lubrication, inertial of load, and phases of the moon
allow. Servos MUST have a "shaft-encoder" in their control-"loop" somewhere
so that the controller (computer, etc.) will "know" where it is at any given
point (so it can control the current precisely to control the location of the
motor's shaft).

A "stepper" STEPS. It is a "gear-shaped permanent-magnet" inside a
stator-core of electro-magnets (the "windings", "coils", "copper", whatever
word to denote that). These coils (generally) conduct DC continuously, and
polarity-switching ONE of them (there are two) will cause a "step". The
motor "stays put" until the OTHER winding's polarity is switched. It then
steps AGAIN. And so on. Or, if you switch the polarity in the OTHER
direction (coil-B first, instead of coil-A), it STEPS in the OTHER direction.

A stepper requires very special "driver/translator" circuitry to run at all,
whereas the servo motor, as I said, can be just-spun around with simple DC.
With the STEPPER, the controller sends some number of steps and ASSUMES the
move desired has been made. No "feedback" to confirm this to the controller.
But the servo and its shaft-encoder ALWAYS "tells" the controller where it
is, how far it has gone, how much is left to go, via that encoder. Ths
requires, then, considerable electronic complexity to "close the loop" with
said "feedback".

The Stepper system is "open loop" (no feedback); the Servo system is "closed
loop" (encoder feedback "closes the loop")

A Gecko is a tan lizard with no eyelids. Really!

But Gecko is a BRAND-NAME of some amazingly-beautifully-built stepper- (and
more recently, also servo-) driver circuits. I have recently received my
first two for controlling steppers, but have not MADE time (can never FIND
it, so must MAKE it!) to connect and test, to see if they function as well as
they look. They are latest-State of the Art "bipolar-chopper" (for steppers;
I know nothing of servo circuitry, theirs nor any others! Duh...).

Lotsa luck! Jan Rowland, Yank Troll



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