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

> 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.

Oops, my mistake.

> 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.

Actually, I think there is a reason to go with the higher encoder
resolution and step multiplying. In a system without a tachometer,
the encoder must be differentiated to find the velocity value to feed
into the servo loop. A fine encoder resolution gives a smoother
position derivitive, and hence a better velocity number. This can in
theory mean better servo loop response (ie, make a fast step move
without ringing).

I do not know how complete the PID loop in the geckos is, ie, if they
will really take advantage of it.

Chris