Re: [CAD_CAM_EDM_DRO] Ferror & minferror

zbushz wrote:

>Well we finally got " the Beast" up and running under EMC2. The
>"Beast" is a Ramill VI, Big Iron, VIA mini computer, running Linux
>(BDI rc-46) Motenc-100 motion board driving brushless AC servos that
>has been in the works for sometime.
>It was running under EMC about a year ago... but we were plagued by
>following errors. I'm wondering if anyone has a good starting point
>for setting "ferror and minferror" in the *.ini file right now I
>have it set at
>ferror =0.100
>minferror = 0.01
>I just looked at the EMC Handbook and I don't really understand it...
>
>Any words of wisdom out there?
>thanks
>Mike Bush
>

I can tell you how the two parameters work, but not too much about how
to tune them for your machine. You should probably post this question
on the emc users list:
emc-users@...
I can say that they (the real experts) will probably need information
about encoder resolution and motor power to be able to help much. Also,
it looks like you're using mm units (0.1" would be a huge following
error) - that kind of info is useful as well.

Here's how they work:

Emc calculates the allowable error as a fraction of FERROR, proportional
to the present feedrate as a fraction of the max feedrate. basically
the calculation is allowed_ferror = FERROR * (current_velocity /
MAX_VELOCITY). If the result of the calculation is lower than
MIN_FERROR, then emc uses min_ferror instead. The reason is that
without the MIN_FERROR clamp, you'd effectively have 0 allowable error
at low feedrates, and the machine would stop all the time with following
errors.

Assuming that you have a MAX_VELOCITY of 5000 mm/M, and you're running
at 100 mm/M, this is the calculation emc would use:
allowed_ferror = 0.100 * (100 / 5000) = 0.002
since 0.002 is < 0.01, allowed_ferror is set to 0.01

Hope this helps
- Steve