GM stepper control strategies

[PHXSYS at aol.com]

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