RE: [CAD_CAM_EDM_DRO] Stepper Math

The step size of the motor is determined by the geometry of the internal poles
and windings and is thus fixed. The drive ratio is also fixed by the gear or
pulley sizes, and the ratio of leadscrew turns to linear motion is also fixed
(by the screw pitch).

As a result, there is a fixed ratio between the full step count and the machine
advance. It is this ratio that is counted as "steps per inch", at least from the
motor's point of view.

For a stepper motor, a "step" is the movement from (only) one phase (winding
set) being fully energized to the next phase being fully energized.
Most of the stepper motors mentioned in this group are either two-winding
bipolar-driven or four-winding unipolar driven (many will argue about this
nomenclature). In either case, there are four phases: after each fourth step,
the pattern of energized windings repeats itself.

There are drivers which can move the motor in amounts smaller than a full step.
They do this by energizing more than one winding set, and proportioning the
current appropriately. The simplest ones can move the motor half a step at a
time, and are referred to a "half-stepping drivers". Some people may reserve a
special name for Quarter-step drivers, but in general anything finer than
half-step (10x is popular) is referred to as "microstep drivers".
In each case the driver moves the motor by the appropriate fraction of a step
for each input STEP pulse. As a result, the driving computer which generates the
pulses must issue 2x, 4x, or maybe 10x the number of "steps" per inch of
movement.

By the way, make sure you are not confusing the "driver" (e.g. Camtronics board
or Gecko) with the "driver program" (e.g. CNCPro or EMC running on a PC). The
"driver" is responsible for the fractional stepping, if any. You must configure
the "driver program" with the net pulses per inch resulting from the combination
of the physical stepper/ratio/leadscrew setup and the driver's fractional
stepping setting.
-Kevin

-----Original Message-----
From: audiomaker2000 [mailto:audiomaker@...]
Sent: February 25, 2002 1:22 PM
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...
...
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?
...
Sean (I know...just hook the darned thing up)