Re: EMC Real World Again

[Ray <rehenry-at-up.net>]

On Tue, 11 Sep 2001, you wrote:
> Well after much discussion with PacSci I know what's happening. The 
> Compumotor Zeta drivers in the machine I have is micro-stepping the motors 
> 25:1 or 5,000 pulses to 200 pulses.
> 
> What will happen if I drop the ratio down to 5:1? How much rougher will the 
> motor run? Will it be noticeable?

My guess is that the Zeta drivers will still switch your motors using 
microstepping technology but just use 5 microsteps per step.  I tend
to think of microstepping as a pair of sine waves 90 degrees apart
with interuptions for as many microsteps as you need.   If you used full
steps, it would still use the sine wave, it would just change the phase one
step rather than several stops along the way, but you should check my
guess against the manual.  

An INPUT_SCALE of 5000 is large but I've seen it run here.  You will have
to test it out for max speed at that resolution with your PC.  Just put
this value in and keep reducing the max velocity until it stops crashing
your computer!  I'd do it here but I've already trashed mine enough today.

> If I go to servos, what are the best drivers? Will the STG board drive the 
> servos direct or do I also need an outside power supply?

You will have significant torque advantage using servos.  Many commercial
machines run more than 600 ipm with large inertial loads.

Don McLane of STG fame recently put a page on
www.linuxcnc.org/handbook/stg/stgindex.html on integration of STG cards and
the EMC.  

The 1997 STG manual states "Keep your current usage to less than 500 ma.
total for the card.  If your current requirements exceed this, use a
separate supply."

Jon Elson's servo card stack requires external power for both the encoders
and the analog signal.

HTH (hope this helps)

Ray