[Bdi4emc-help] Quickstep driver

Matt Timmermans matt at timmermans.org
Thu Feb 16 05:05:26 CET 2006

> Quickly threw an emc-modules package together containing your driver and
> another tweak to the trajectory planner - This is already up on
> http://bdi4emc.ourproject.org/debian and should hit the other mirrors
> sometime in the early hours. [...]

That was fast -- I'm glad to see it up so soon!

A note on setting PERIOD for the quickstep driver:   My 3.2 GHz P4 (that 
doesn't actually run any machines) likes PERIOD=7us.  The P266 laptop that 
runs my Sherline likes PERIOD=15us.  The laptop can actually run with 
PERIOD=10us, albeit slowly, so that's probably the best bet for the 1.x GHz 
class machines that are often used with EMC and steppers.

15us is probably a good .ini default, since it works on low-end machines, 
and it is really plenty fast.  I spent a bit of time this morning watching 
the Sherline zip around at 48 ipm using that setting, and those little 
handwheels spinning around at 960 RPM convince me that you really wouldn't 
want to drive a stepper system any faster.  I got worried about damaging the 
thing, throttled it back to 24 ipm, and tightened up the gibs as a penance.

With the module package available, anyone who uses freqmod in STEP/DIR mode 
with <= 4 axes and wants to try it should be able to do so like this:

- install the new emc modules package;

- make a copy of your current .ini file;

- edit the new copy and change EMCMOT=freqmod to EMCMOT=quickstep;

- change the PERIOD setting to 0.000015 or 0.000010 if you're brave;

- change the MAX_VELOCITY settings in TRAJ and all the AXIS sections to 
whatever you want your rapid speeds to be;

- If you set your rapids fast, make sure the acceleration limits are 
realistic, or you could miss every step in a rapid move.

All of your other settings should carry over.  The PID settings aren't used, 
so it doesn't matter what they're set to, and you don't have to do any of 
that tuning stuff.

To run,  in /usr/local/emc, do ./generic.run -ini new_ini_file.ini.

Caveat:  EMC currently ignores acceleration limits while doing backlash 
compensation, and it does it at the axis rapid speed.  That's fine for 
servos, but not so nice for steppers, so if you have backlash compensation 
set, you may miss steps there if your rapid speeds are too high.  I'll put a 
strict enforcement of the acceleration limits into the quickstep driver 
sometime soon.


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