Stealthchop2 to Spreadcycle switch



  • I run stealthchop at quite high speeds. about 80mm/s
    When i switched to 0.9degrees steppers the setting was lowered.

    The problem is that when the driver switch between stealthchop and spreadcycle at high speed this causes a loud noise and in my case layer shifts. After i increased the limit so that it would not switch, i had no layer shifts.

    Currently the switch is done via setting the TPWMTHRS parameter and the switch is done by the trinamic driver.

    Would it be possible to do the switch based on the requested speed.
    So i.e Print move at 60mm/s -> Ok remain in stealthchop
    Travel move at 150mm/s -> Switch to Spreadcycle, then move.


  • administrators

    Do you mean switch to spreadCycle at the start of a move that is planned to exceed the threshold speed, instead of switching when the threshold speed is exceeded?

    It might be possible, but it would require move-by-move reprogramming of the drivers via the UART. There would be some latency between the start of the move and the command reaching all the drivers. It will be easier to do on Duet 3 because the drivers will use the faster SPI instead of UART for reprogramming.



  • @dc42 said in Stealthchop2 to Spreadcycle switch:

    Do you mean switch to spreadCycle at the start of a move that is planned to exceed the threshold speed, instead of switching when the threshold speed is exceeded?

    yes with some intelligent logic. i.e if its already in the required mode then dont issue the command.

    do you know that the latency would be?


  • administrators

    Off the top of my head I think the latency should not exceed 10 milliseconds. I will need to check with Trinamic what happens if you reduce TPWMTHRS when the motor is in stealthchop mode and already moving above that speed.



  • from the TMC documentation: https://www.trinamic.com/fileadmin/assets/Products/ICs_Documents/TMC2130_datasheet.pdf

    A jerk occurs when switching at higher velocities, because the back-EMF of the motor (which rises
    with the velocity) causes a phase shift of up to 90° between motor voltage and motor current. So
    when switching at higher velocities between voltage PWM and current PWM mode, this jerk will occur
    with increased intensity. A high jerk may even produce a temporary overcurrent condition (depending
    on the motor coil resistance). At low velocities (e.g. 1 to a few 10 RPM), it can be completely
    neglected for most motors


 

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