That is the problem with trying to use torque command input with a PID. The FF1 setting is very speed dependent. What works well at a low speed will be way way too much a higher speed (enough to cause following errors.) In a velocity command system the command required to move increases linearly with the speed, but in a torque commanded system it is anything but linear. In fact it is even possible that the amount of command input needed to maintain a low feed rate might be more than is needed at a higher feed. For the most part, at least theoretically, once you've overcome friction the amount of force (torque) needed to maintain an achieved velocity is zero. In practice it still usually takes more electrical force (current) to spin the motor faster. That is where I thought that limiting the FF1 by setting a value for "pid.N.maxcmdD" might be useful.
If you want to add that as a tunable item in the Axis Calibration window, add these lines to your hal and ini files
In the Hal file in the x axis section add:
setp pid.N.maxcmdD [AXIS_0]FF1LIMIT
and in the ini file in the [AXIS_0] section add this line
After restarting Linuxcnc you should see the new line in the Calibration window for FF1LIMIT with an initial value of 10. I really have no idea what might be a good starting value. start with a higher value, then with the FF1 working well at a low speed lower the ff1limit incrementally until you start to see some effect from it. Then set it to the smallest value that doesn't do much. Then test to see what happens when you increase the velocity of your moves. If this works/helps, then you can make the same changes for the other axis.
I really have no idea what this is going to do, it may not work at all. I have never tried it myself. I gave up trying to make a single PID loop work with a torque command on my machine years ago. (But I hadn't thought of trying this back then and I was much greener at setting up Linuxcnc.)
