RE: [CAD_CAM_EDM_DRO] EMC: why do I have so many problems?

> -----Original Message-----
> > 6: as the prospect of servos becomes greater, does it seem more
> > logical to use step and dir outputs with a geckodrives or is there an
> > advantage to using emc to monitor the encoder itself
>
> You mentioned you had a 200 mhz computer, which is kind of slow to run
> a stepper system as generating fast step rates creates a lot of
> overhead. If you go to the Gecko servo drive get the one with the
> step multiplier. Still you will have to choose an effective step size
> that is no bigger than your desired positioning resolution, and that
> may require you to still run at high step rates. EMC could be
> rewritten to run the step/dir geckos a bit faster since they don't
> care about nice regularly spaced pulses, but I don't think that's been
> done and might not be easy.

From experience with EMC and Gecko G320s a 200 mhz system will run the
drives plenty fast if you use steppermod.o instead of freqmod.o. There is no
reason to be rewriting EMC to achieve this. Steppermod.o is the original
stepper drive module and it can put out the pulses quite rapidly, but it
suffers from ragged spacing at high step rates. Big problem with steppers,
but the G320s don't care as the steps just drive an accumulator. So, it is
already done and is actually easier to set up than freqmod.o because you
have no PID tuning to mess with.

While the G340s (pulse multiplied version of the G320) are a great unit I
think that they get recommended all to often for all the wrong reasons. If
you are buying the encoders my preference is to get a line count encoder
that at the maximum feed rate you want will be achievable toward the top
step per second output of your software. All a G340 will allow you to do is
drive a setup that requires a higher step per second rate than your software
is capable of outputting. It will not do dittilie to increase the accuracy
or precision of the machine and does add $30 more to each drive. Well worth
it if the alternative is to spend $50 - $100 per encoder to get the step
rate where you need it, but a waste if you think it is doing more than
allowing you to use the encoders you have on hand.

Tim
[Denver CO]

P.S. I have a couple of sets of the old G201 stepper drives not yet spoken
for. $215 + $8 shipping for 3 drive on orders committed to by the end of
today.

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