Duet3: TMC driver current setting after power cycle



  • I have a quick question regarding how the Duet3 handles a power cycle on the main Vin rail (as in for example turn the main power supply off with the MCU still powered via USB and then back on)?
    Specifically I have the experience with a different board running Klipper that after a power cycle you need to call a TMC_INIT command manually in order to reset settings like RMS current of the TMC drivers, as they would reset when the main power rail is cycle. This did cost me a rather hard to get small motor as it burned out in a very short amount of time (only handles like 0.4A RMS). I'd like to avoid this mistake from the start 🙂

    So with the duet3, will I need to call any commands after power cycle or does the firmware handle this gracefullly, as in automatically detects Vin power cycle and configures drivers automatically?


  • Moderator

    If the Duet is still powered it would still have the configuration from config.g loaded. When vin is reapplied the motors would likely be in an unhomed state from being deenergized, so you would need to home them again any way and the current setting from config.g would still be in effect. At least that's what I think is going to happen.



  • Well, the problem I ran into with Klipper, was that while klipper still knew about the current setting, but the TMC driver forgot about it. Since klipper had no means to know if Vin is present, it also had no means to know it had to instruct the driver again about the current settings. I am aware that the Duet3 monitors the input voltage.

    @Phaedrux said in Duet3: TMC driver current setting after power cycle:

    At least that's what I think is going to happen.

    Thats exactly what cost me a not exactly cheap and especially hard to source Nema8 motor 😉 Hence I figured it's best to ask before I go to just find out by trial and error ...


  • administrators

    All Duets from the Duet WiFi onwards monitor the VIN voltage, and RRF re-initialises the TMC drivers whenever it goes above about 10.5V. As @Phaedrux says, all axes will be in an un-homed state.



  • Nice, thank you @dc42!


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