Position Shift with Servo Motors

General Discussion
1

Basic Information:

Printer Model: Selfmade
MCU / Printerboard: mks skipr
klippy.log (7.6 MB)

klippy.log
klippy.log (7.6 MB)

Describe your issue:

Hi Klipper community :slight_smile:

I have a selfmade 3D Printer running since about 3 Years.
it has a build volume of 610x700x1100mm. this is why I decided to use Servo motors ( Servo42B, now D version on X, JMC servo on Y and Z)
in the beginning I used Marlin and some weeks ago Marlin Update offered Input Shaping. The problem was that the Y Motor (JMC Servo) lost its position. I could 100% figure out that the problem only occurred when input shaping was enabled.
behavior: at every direction change, the position was shifted about 0.1mm to thy Y pos. direction. you could see the effect on the first layer already. continuous position shift to the Y+ direction. I switched to MKS Skipr board with Klipper, same here. without Input shaping no problem. As I want to use the input shaper, the workaround is to use a nema23 closed loop ( Servo 57D) on Y axis but I don’t like it, too noisy. Any ideas why the JMC Servo offsets is position at direction change with enabled input shape?

Sorry for my english and thanks in advance!

2

Hello @GSBy !

When it works with a different motor, have you cross-checked (on a different axis), that the desired motor has no issues.

3

Hi Ewald, the motor printed well after disabling input shaper. and yes, I tried another JMC servo on this axis, same behavior. both tried servos are in another machine, no problem.

4

So, Marlin and Klipper behave the same, i.e. as soon as IS is activated it comes to this effect?

5

Yes, this is exactly what I want to describe

6

Seems strange. Maybe @dmbutyugin can chime in and has an explanation.