John Figie Ralph Stirling wrote:
> > > Personally, I am more interested in the approach you've been > advocating for years, of having a microcontroller per motor handling > commutation and drive, with the Linuxcnc/Mesa setup sending > step/direction pulses or communicating via sserial or Ethercat with > each motor. I've built a number of mosfet bridge boards for 2 or 3-phase > drive of small motors which have been good enough for in-house use, > and it isn't too difficult. Making them bullet-proof for other end-users > to connect to their own motors and power supplies would require some > design hardening. > > > I somewhat agree, but I think rather than send step and direction just send positions at a fixed rate, say 1 msec or even slower then linuxCNC does not need to do step generation. This also has the advantage of having no limit to the position resolution of a step size. In addition it is possible for the drive to interpolate positions if a slow update rate is used - but this creates some challenges with synchronization with other independent axes such as a spindle - but not impossible. This is the way that CIP motion over Ethernet drives work and I think many Ethercat drives work as well. If the drive is handling the closed loop position then the motion planner - LinuxCNC only needs to send the positions at a fixed frequency and does not need to do any closed loop control. The motion planner never allows accelerations to exceed the capacity of any of the drives. If a drive cannot for some reason follow the plan then it faults, signaling the motion planner to stop. A drive could also run step motors in a closed loop by the drive. But of course step motors have limitations to the max speed because they are effectively like large pole count motors. Just my 2 cents. John Figie _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
