Force feedback shuttle control
 

I have a couple of small steppers -- 20 oz in or thereabouts -- that I think
would serve dandy as force feedback motors in a custom jog shuttle
controller. I want the shuttle wheel to resist turning proportionally to the
mill's stepper current draw (or torque, or whatever meaningful measure there
is of how hard they're working). It doesn't have to be very precise, but
precise is good also.

How do you control a stepper in this fashion? Operation will mostly be in
quadrant 2, plus return to center when it's let go. I think I would like it
to be switchable between operating in velocity mode -- turn more to go
faster -- and position mode, emulating a hand wheel or crank.

Any thoughts on how to do this? Or which of the many boards or newsgroups
might discuss something like this? I realize I might have to program a PIC
to do this on the cheap, but off the shelf would be nice too.

--Might try posting this to comp.robotics.misc as there are a
lot of stepper motor hacks over there..

--
"Steamboat Ed" Haas : You just can't beat
Hacking the Trailing Edge! : cruisin' in a steamboat
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

I'd rather not use a stepper motor for this job. When you push back on a
stepper hard enough, the shaft then steps back to the previous phase that
matches the power being put into the motor.
I'd rather get a large diameter/high torque DC motor and drive it with a
small fraction of the rated power (maybe 2V max. on a 12V motor) to provide
a resistance to the motion. An old cordless drill motor will probably be
very nice for this job.

--
Why do penguins walk so far to get to their nesting grounds?

"Bob May" wrote in message
...
I'd rather not use a stepper motor for this job. When you push back on a
stepper hard enough, the shaft then steps back to the previous phase that
matches the power being put into the motor.
I'd rather get a large diameter/high torque DC motor and drive it with a
small fraction of the rated power (maybe 2V max. on a 12V motor) to
provide
a resistance to the motion. An old cordless drill motor will probably be
very nice for this job.

I think you might be right, although I think I can easily monkey with the
current sense pin to vary the holding torque. Voila, instant feedback.
Problem is measuring what it's feeding back. The steppers they're
controlling/feeding back are driven constant-current, and I see no easy way
to measure how hard they're working. (Probably just yet another reason to
upgrade to servos.)

Actually, the problem to solve was not so much a need for tactile feedback
on a jog shuttle, but what to do with a pair of small steppers. Paper weight
or trebuche fodder comes to mind, but think now I'll probe for ideas. What
absolutely cool things can you think to do with a pair of 42mm square, 20
oz.in. steppers? I have suitably sized controllers and drivers, as well as a
14 pin PIC programmer.