Autotune_tmc -- Adjustment of parameters if 2 motors in parallel

General Discussion
1

Basic Information:

Printer Model: DIY
MCU / Printerboard: Kraken V1.1
Host / SBC: RPi 4

Describe your issue:

I would like to use the autotune_tmc function to configure my drivers at GitHub - andrewmcgr/klipper_tmc_autotune: TMC stepper driver autotuning Klipper python extra

I am placing two motors, the ldo-42sth60-3004ah Kraken V2, in parallel on one driver, using the Big Tree Tech Kraken V1.1, which has TMC2160 drivers (which are configured exactly the same as TMC5160 drivers). I have the motor constants below for 1 motor, how should they be adjusted (if at all) if two motors are in parallel on the same driver?

[motor_constants ldo-42sth60-3004ah]
resistance: 1.0
inductance: 0.0016
holding_torque: 0.8
max_current: 3.0
steps_per_revolution: 200

Thanks!

2

We do not support this modification. In addition, I would consider the “tuning” of it at least questionable, if not in places outright contradicting the TMC specifications.

My personal advice: Be very careful with such one-click solutions, especially if they:

  1. Lack transparency about what is changed and why.
  2. Lack references to official documentation, e.g. by Trinamic
  3. Choose settings that diverge from conservative interpretations of TMC specifications.
  4. Make claims that lack independent, quantitative validation.

Also refer to: SpreadCycle and StealthChop (an advanced guide)

3

Are the TMC2160 supported by GitHub - andrewmcgr/klipper_tmc_autotune: TMC stepper driver autotuning Klipper python extra?

I don’t think this Adjustment of parameters if 2 motors in parallel · Issue #272 · andrewmcgr/klipper_tmc_autotune · GitHub is the right place to ask for help.
I would ask an FAE from ADI (they bought Trinamic) for support. If you’re lucky, you might get the answer for your plan.

4

Thanks for the input!

I believe autotune_tmc is doing what one could do manually using this spreadsheet, I have not attempted to use this spreadsheet yet: https://www.analog.com/media/en/engineering-tools/design-tools/tmc5160_calculations.xlsx

I have run stepper motors in parallel several times before with no issue, but these are 60mm tall NEMA 17 motors and would pull max 6 amps total if two in parallel (8 Amps available on Kraken V1.1). Another option would be to add an extra control board and forego putting the stepper motors in parallel. I am concerned there will be resonances or other issues when running larger motors in parallel, also the total length from the control board to the stepper motor is ~2 meters. I have shielded motion certified cable of sufficient gauge, 18AWG, that both steppers are in parallel on, and the wires will all be the same length (~0.5 meters) to each motor when branching off the 18 AWG wire. Unfortunately, the shielded wire doesn’t have twisted pairs inside it.

Just curious if any advice on running large motors in parallel with long wire lengths.

Thanks!

5

The only advice I can give is not to do it all. Stepper drivers are complex current regulators, and a parallel connection messes them up. No two motors are perfectly identical, so even small differences in their electrical and mechanical characteristics will multiply their effect on the current.

You risk:

  • Imbalance in the current
  • Imbalance in the torque
  • Massively degraded control capabilities of the driver
  • Lost steps potentially going up to desynchronizing the motors
1 Like
6

As a follow up: We have extended Stepper Motors in 3D Printing: Characteristics & Practical Guidelines in particular with the chapter 7. Wiring Stepper Motors in Series or Parallel

Unfortunately, this is not the case at all.