@dmbutyugin - at Porting some idea's to Klipper, freq / amp modulated output shaper, (can someone suggest a proper name for this methodology?) - #7 by dmbutyugin you indicated that you saw a repeating pattern by phase during your accelerometer analysis.
I also saw a repeating pattern - as can be seen in the “HEND graph” above. There does appear to be a correlation between accelerometer and stepper phase, as well as a correlation between angle sensor data and stepper phase. There is also a pattern in the forward and reverse direction - and indeed the pattern seems to change slightly based on direction. It’s not entirely clear to me if the change in pattern due to direction change is due to a systemic difference or due to run-to-run variance. (Though stepper motor lag definitely dominates the angle sensor data and that is clearly influenced by direction.)
-Kevin