Effect of FF1 varies with feed rate?

After emprically setting [JOINT_n]OUTPUT_SCALE such that FF1=1.0 was well compensated I found that changes of the feed speed effect the compensation.

For f200 (metric) FF1=1.0 gave good compensation:



At f350 the compensation is not so good:



I assume the cause is non-linear response of OUTPUT_SCALE to different commanded speeds, or is this the expected behavior?

The nonlinearity is more likely in the PID output path somewhere
(not in LinuxCNC)

forum.linuxcnc.org/10-advanced-configura...-how-to?limitstart=0
If you read the above thread, it is explicitly mentioned that ff1 will change with any change to other parameters. It has to be set at low feeds and gradualy calibrated with higher and higher feed rates, only after the scale and P factor had been set.
If i remember correctly, for the FF1 to be 1 there are several other parameters that need to have the needed value. From your post i think that you did exactly that, but if it changes with feed, something is not quite as it should be.
I can not dwel into more detail as there are way more qualified members on this forum for that.
Regards,
Tom

PCW wrote: The nonlinearity is more likely in the PID output path somewhere
(not in LinuxCNC)

I think the non-linearity is the servo response to the analog voltage signal. I am just mapping that now.

Does there already exist a look-up-table that can be applied to correct for the amplifiers response curve?

Yes, the lincurve component is designed for this kind of thing

Quick-n-dirty yet surprising linearity results. Both axes have the same hicks?

Hmm...