GM stepper control strategies

[Peter D. Hipson]

I think you figured it out all ready. Actually it steps the motor well
beyond the end (a mechanical stop prevents movement, however). This leaves
the motor at a known position (end) and since the CPU knows how many steps
are needed to get to a specific position, the rest is easy. When designing
this type of circuit most engineers step twice the maximum number of steps
to be sure that they are really at the end stop.

When you boot your PC, that grinding noise you hear from the diskette drive
is the same thing, pull the head back to the stop, then pull back more just
to be sure.

At 09:22 PM 9/15/1999 EDT, you wrote:
>Hi
>
>
>I know that GM uses an linear stepper for  idle air control, at least  older 
>models. I know that it has no position feedback and it can go to specific 
>positions at startup. I think it drives the motor to one position, either 
>fully extended or retracted and then counts from there. I don't know how it 
>knows when it is fully extended or retracted?
>
>Any ideas?
>
>I want to control a linear stepper motor to control the spring rate on a 
>diaphragm. The The position will change based on analog inputs , pressure
and 
>flow rate. The system will learn the best postions at different analog 
>values. Most of my experience is with servos, so I've got a couple of 
>questions.
>
>1. How do I keep track of the stepper position?
>
>2. I want to program a default position on startup, is there a way to get
the 
>same position each startup without the use of electronic position feedback?
>
>3. I guess if you know the start position you can create  variable to count 
>steps, but what if an external event moves the position?
>
>
>
>Thanks
>
>Jon
>
>
Thanks, 
        Peter Hipson (founder, NEHOG)
        1995 White NA Hummer Wagon