Re: RA calibration

[Tom Droege <tdroege@veriomail.com>]

Mike,

One more thing.  If you home the RA drive, it goes at some indeterminate 
rate that is determined by a program loop.  It moves a step, then looks at 
the limit switch, moves a step ...   I have never actually timed it but it 
goes at about 14 times normal based on the time it takes in my "follow" loop.

So the answer is, it depends.  You can run it at exact binary ratios.  You 
can use the home RA feature to go at an indeterminate (but probably quite 
constant) rate.  You could keep track of how far you are away from home and 
go back to near home at the full 32x rate, then when you are close switch 
to the "find home" mode.  Note in my code I put in various things to try to 
eliminate backlash.  You might also want to do this.  The coupling to the 
stepper motor is a piece of rubber tubing.  This greatly reduces vibration 
from the stepper.  Rubber being the right stuff for this purpose.  But it 
is not rigid, and there is some significant "soft" backlash built in.  You 
can probably not count on it being constant over temperature or stickiness 
of the screw lubrication, etc..

I would find home using the limit switch.  Then I would always go forward - 
say 100 steps.  Then I would call that home.

Sending this to the list also as some others might need to know it.

Tom

At 04:08 PM 1/13/02 -0500, you wrote:
>Hi Tom,
>
>I'm trying to calibrate the RA drive for my software and would like to know
>how fast the fast forward and rewind speeds are in comparison to the normal
>tracking speed.  Is it a strict ratio?
>
>Thanks,
>
>Mike G.