On 10/02/2010 07:05 PM, Jim Thompson wrote:
On Sat, 02 Oct 2010 20:23:17 -0500, wrote:

On Sat, 02 Oct 2010 23:00:45 GMT, (Nico Coesel)
wrote:

Jim
wrote:

_Vague_ Stepper Motor Question:

What is the maximum rate one might expect to step from phase to phase?

Depends on the maximum dissipation. I did manage to get a big stepper
(2.5A) to about 6000 steps/s (1800 rpm) with a single ended driver.
But it was necessary to ramp the speed up& down. Nowadays I think I
would use a servo motor with a position encoder or at least drive the
steppers with a full bridge PWM and feed the motor sine waves unless
halted at some point. The biggest problem with steppers is that you
can miss a step and you have no way of knowing unless you add the
encoder.

Just a passing thought but seems to me it should be theoretically
possible, at least, to detect step movement by the inactive coil's
back EMF.

My 3-phase motor driver for Bosch/Mercedes did exactly that... and
used it for commutation.

It's commonly done for 3-phase brushless PM motors. I don't know if
it's been done much for steppers, although I'm sure that _someone's_
tried it.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html