Tuning servos, What speed and what to do about an ferror spike

So I'm finally to tuning my servos, and I was wondering at what speed do you guys do your final tune? My rapids can go as high as 400ipm, but the FF1 at 400ipm is different than at say 100ipm. Also, I have this weird spike in my FError plot, right at the beginning of the move. It's even an audible thud. What do I do about this? I have high P (150), FF1 of about 1.5 and FF2 of .008. It's similar across all axes. I can go higher in P too. What value do you have set for your following error faults? Is there any way to get the values to persist in PNCConf? I tuned in Axis, save to file, and it persists there, as long as I don't rebuild the config in PNCConf, but I have more work to do in PNCConf.

Thank you

If the FF1 number is different at different speeds this likely indicates a
non-linearity in the servo drives velocity command response. It could be
caused by low velocity loop gain in the drive so that may be something to look into.


A small error spike at the beginning and end of motion is a undesirable side effect of
LinuxCNCs trapezoidal velocity profile. You can reduce the size of this by lowering the
acceleration.