Closed loop tuning with multi-driver axis

[ErlerPrint3D]

Hi,
I am currently building a large 3D printer with an axis system like the one used in the Annex-Engineering K3 (https://www.youtube.com/watch?v=75OxlE8eso8&ab_channel=AnnexEngineering). This means 2 axes for X and Y. The axes should run with quadrature encoders in closed loop mode (Duet 3 Expansion 1HCL). As I currently have to calibrate each motor individually and my system is relatively stiff, so I get backlash values of 0.25-0.35 (firmeware limited is 0.22) for the calibration movement (M569.6 P50.0 V1). Depending on where the machining head is positioned, the resistance for the motor is lower and I was also able to achieve values of 0.2. But I can't do that for every motor. I also use the maximum current for the motors and have also tried to calibrate a motor when all others are currentless to exclude the counter forces but without success.

Does anyone have any experience with this or any ideas what else I could try?

@dc42: Will it be possible in the future to calibrate axes with 2 motors at the same time?

[T3P3Tony]

@ErlerPrint3D This is an existing feature request:
https://github.com/Duet3D/RepRapFirmware/issues/758

T3P3 created this issue 24 Apr 2023, 18:52 in Duet3D/RepRapFirmware

open EXP1HCL: support using two 1HCL boards on the same axis. support coupled closed loop tuning #758

[usinjin]

@ErlerPrint3D Did you find a solution to your issue? I am having a similar one.

[dc42]

@ErlerPrint3D my recommendation is to use the Duet3D magnetic encoder instead of quadrature encoders. That way you can calibrate each motor individually, before fitting the belts that couple them together; and you won't need to execute a tuning move each time you power up. The magnetic encoder also has much higher resolution that quadrature encoders.