On Wednesday 13 March 2019 20:28:43 andy pugh wrote:

> On Wed, 13 Mar 2019 at 23:45, Gene Heskett <ghesk...@shentel.net> 
> > > When I have considered doing it I have thought in terms of a
> > > semi-circular track and an opto-sensor. (so it never takes more
> > > than 180 degrees to home)
> >
> > In other words, a grey scale with enough opto's it knows where it is
> > w/o moving at all.
> No, a single sensor and a 180 degree target.
Ahh, white turn one way, black the other. But once the boundary is 
encountered, do a fixed edge sequence so it always hits the stop from 
the same direction. That would also lend itself handily to an accurate 
scale determination which is another problem. I like that. I have the 
scale calibration in hal code, used for calibrating the spindle scale on 
the g0704 when I put an encoder on the rear of the motor, but left the 
index on the spindle.  So the scale is about 7000 in high gear, and 
about 14000 in low. I can use plumb ridiculous Pgains, and speed is very 
very stiff. What did you make the target out of so it didn't wear 
mechanically screwing up the opticals?

Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>

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