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> Van: Bob Bullock <bobb@PROSTYLE.COM>
> Aan: PICLIST@MITVMA.MIT.EDU
> Onderwerp: What exactly IS a step for a stepper motor
> Datum: woensdag 8 juli 1998 22:46
>
> My current PIC project requires the use of a stepper motor so I have been
> busy learning about steppers. My motor is of the Bipolar type (Airpax
> LB82773-M1) with a step angle of 7.5 degrees (48 steps per revolution).
> When I implemented my test program, I found it rotated 4 times the
expected
> rotations.  My conclusion is that my assumption that cycling the stepper
> through the 4 different control patterns equaled on step is wrong and
that
> each different pattern is in fact one step.

Correct.

> If this is the case it begs a few questions:
>
> 1) In order to stop the stepper at any of the 7.5 degree steps I will
have
> to be able to stop the motor at any one of the four control sequences.
If
> this is the case, do you have to keep track of this and start the next
> movement with the next control sequence?

Yes.  Normally you keep the motor powered so that the axis stays firmly at
it's
position.  If you remove the power the axis could be rotated fairly easy

> 2) Assuming the answer to question 1 is yes, then what about when you
power
> up and don't know what step point it is at?

You initialize.  Move the {whatever is atached to the Axis} to a
'calibration position'.  Sense it's presense there with a Micro-switch or
opto-coupler.
That's what a Plotter or current (laser) printers do.

Another option is a Gray-code wheel that will give you an absolute
(rotation) position.  But a 48 step rotation means a 6-bit code (and
cables).

Greetz,
  Rudy Wieser