RE: [CAD_CAM_EDM_DRO] Stepper Math

Yes, Sean.

the drives can change the number of steps it takes for one revolution of
the motor.

The common motor is a 200 step/revolution as a base value. When it is being
driven by a drive that runs in "Full step mode", it will take 200 pulses to
make it turn one rev. This is rarely seen/used.

You are most likely to encounter a drive that runs in "Half-step mode",
meaning it will take 400 pulses to make one rev. The motor just follows that
and stops at every half-step instead of every full-step of its 200 steps.

Likewise, there are drives that run in quarter-step, eight-step, or tenth
step like the Gecko G201. You are now at 2000 pulses per revolution. Your
motor runs 10 times slower than on a full-step drive but it is 10 times more
precise (theoretically) and most importantly, much more than 10 times
smoother.

The speed versus resolution is a compromise you have to make, but the
smoothness factor of fractional step drives is maybe more important,
depending on your application.

Hope this helps,
Guy


-----Original Message-----
From: audiomaker2000 [mailto:audiomaker@...]
Sent: Monday, February 25, 2002 10:22 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Stepper Math


Hey all,

I must say that I thought I had this down, but after learning more,
I think I know less again (funny how that works eh?)

My question is in the relationship between the computer's pulses,
the drive's pulses, and the step motor's steps...

Let me start with my point of reference so we can see where I'm
screwing this up....
The older Nema 42 steppers could be jogged in tenths in the original
configuration. The lead screws are solidly shrouded on the machine
so I'd rather not tear it down to get to them to count TPI, but
based on any realistic thread pitch, I'd say that the motors
probably had to do more than 200 steps per revolution to advance in
tenths.
The first thing I don't get is if the drive can change the amount of
steps a motor takes in a revolution, or if that is limited by the
stepper itself? It seems like it should be the drives making this
decision (universal bipolar motor having it's fields arranged for
microsteps by the drive), and if this is the case, how does the
drive know how fine a step the motor is capable of, or doesn't it
matter because it's all about the drive?
Or does the Stepper have a finite set amount of steps per revolution
and the drives simply send generic pulses as fast as they can, with
the drives that can send them reeeeeally fast being
called "microstepper drives?"
Without rewiring, what is the constant here? It seems to me like
both the stepper and the drive are constant and only the speed of
the stream of steps from the controller is the variable... is this
correct? If the drive could be programmable for the size of the step
(rotation angle), I would understand that because it would shift the
fields in just the correct way to acheive that advance on the
stepper, and you would set it to the maximum advance (or step
resolution) that your stepper could accomplish.
What I'm missing here is what is fixed and what is variable. Do the
drives have a set number of field configurations or advances and the
steppers just follow along so now you have to program your steps per
revolution based on the drive?

Yikes... I'm lost again.

Sean (I know...just hook the darned thing up)

P.S. By the time you respond to this, I will have visited 5 more web
page tutorials on steppers, figured it out in 3 conflicting ways and
started at zero again.


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