John, I am certainly no expert and defer to your expertise. I did not mean to imply that the motor lost steps, but meant it never received the step since it was consumed powering up the driver. I was bedeviled with my Z axis never keeping position (it either went too high or more often too low) during a prolonged cut sequence. I broke a dozen endmills early on trying to flush out the issue.
Kim Mortenson's writeup describes the methodology of the HCNC board with the Allegro SLA7070M series chip. THe write up is found here http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?HobbyCNC I would certainly be interested in any thoughts / expertise on this issue. Brian PS - Not sure why your post came marked as ***SPAM****. GMAIL would not let me correct the header (or more likely I do not know how to correct the header using gmail). 1. Stepmotors cannot loose one step, but the driver can. A 1.8 degree 200 fullstep/rev motor can only slip in increments of four fullsteps to one of the 50 indent positions per revolution. 2. Drives can loose or gain steps for several reasons, but one common cause is noise on the input lines. In the old days (before 9/11) the input opto-coupler acted as an effective low pass filter with about a 200KHz cut-off frequency. New opto-couplers are good up to 15MHz, and unless the driver design includes a simple low-pass filter, there can be lots of false steps. 3. I never used a simple RC for current reduction. It was either a timer IC or a timer function in the microcontroller. The response to full current was typically less than one millisecond, and this did not give a problem unless the motor was supporting a load that could produce a torque overload at the reduced current. If that was the case we did not use the current reduction feature. Regards __________________________________________________________ John Harris E-Mail [email protected] ------------------------------------------------------------------------------ Doing More with Less: The Next Generation Virtual Desktop What are the key obstacles that have prevented many mid-market businesses from deploying virtual desktops? How do next-generation virtual desktops provide companies an easier-to-deploy, easier-to-manage and more affordable virtual desktop model.http://www.accelacomm.com/jaw/sfnl/114/51426474/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
