AMC drive tuning

OT-CNC wrote:

Jon, thanks. That explains why .004" inch or so would work for my settings on the XY and a tighter setting on the Z screw mounted encoder.
Correct me if my understanding is wrong, following error has nothing to do with the accuracy of linuxcnc as it tries to have 0 error but is a flag to stop movement when the error exceeds the set point.

Yes, that is right. Following error from the PID is the instantaneous difference between commanded and actual position. MIN_FERROR is the base limit of permitted error for that axis. FERROR is an addition to the limit proportional to velocity.
So, if MIN_FERROR = 0.003 and FERROR= 0.001, then .003" of difference between commanded and actual position is allowed at standstill. At 120 IPM feedrate, that is 2 IPS, so 2 X .001 is added to the allowable error, and you can have up to .005" or error at that speed. This allows more error when in rapid traverses, but tightens the limits at cutting feed rates.

My f error plot shows the spike on start of acceleration, I set my value above that. In other words, a setting of .004" would trip at .004" and above. When not tripped, it has no affect of arriving at the target say .004" short or too far.
Now, how does the trajectory planner come into effect on this for tuning? Should tuning be done with exact stop mode or does it not matter?

The FERROR parameters have NO EFFECT on tuning, they just affect how much error is permitted before stopping movement and reporting an error. The trajectory planner also has no knowledge of following error. It produces interpolated positions at the servo rate of ideal position. The PID component gets these positions and also the actual position reading, and tries to compute the best velocity to command to get the minimum error on the next servo cycle.

Last, sorry, the newer INIs have 2 sentries of the same max velocity, max acceleration, min and max limits under axis and joint. I assume that's for backwards compatibility? I think when I save the settings from the calibration screen it just updated the joint section. Can I delete that axis section or just duplicate the values over?

No, not backward compatability. When first started, LinuxCNC is in joint mode, once the axes are homed it switches to Axis mode. There really isn't a lot of distinction on "trivial kinematics" ie. cartesian machines, but there's a huge difference on robots and other angular joint machines. But, for that reason, there are different velocity and accel params for the two modes.

Jon