Re: [CAD_CAM_EDM_DRO] EMC Following Error

David Micklethwaite wrote:

> I am trying to get EMC working with a small mill. I have Gecko G320 drivers
> and am using steppermod. I can jog the axes back and forwards by the amounts
> I expect and in the right directions. However, I occasionally get following
> errors and do not understand why.

Steppermod does not simulate a servo system, as freqmod does, so it can't get the
following error from anything having to do with the acceleration, PID gains, etc.
But, it DOES have a limit of how fast it can put out pulses. Your input scale is very
high, 32000 steps/inch. For 1.2 IPS (Inch/Second) velocity, that requires 38,400
steps/second to be issued from the computer. You don't report what your PERIOD
parameter is set to, but it needs to be REALLY high. I think it needs an absolute
minimum of 38.4K x 2 = 76800 per second, or 0.00001303 seconds/interrupt.
But, this will make the jump between the next lower velocity and top velocity a
2:1 jump (from 19200 steps/sec to 38400) which will drive steppers nuts.
Maybe the G320 will not have a problem with this, but it might still cause
problems in getting a steady speed, as the steps will be jumping around in
timing. Anyway, that period comes out to 13 microseconds, meaning the CPU
gets an interrupt for the stepper task every 13 uS. I think you'll need an 800+
MHz Pentium III, minimum, to run at this rate and still keep the rest of EMC and
Linux functioning.

If by following errors, you mean that the Gecko drives trip out, then your acceleration
parameter is WAY too high. 20 Inch/sec/sec is More appropriate for a high-end
pen plotter than a machine tool!

Jon