Stall detection setup



  • I am trying to work out stall detection for my printer in conjuction with my scheme for Z-Probe pickup (different thread). I want to enable it as a failsafe for the condition if the probe is not picked up and the machine overtravels.

    I am not clear on 2 things- if microstepping values affect the stall detection and Hmin. I am on Duet2 Ethernet, RRF 3.1.1, 24V psu if it matters.

    My Z axis is TR8x8 screws that are driven by a belt reduction system. Here is the bit from my config.sys file for motors and esteps.

    M350 X16 Y16 Z32 E16 I1                        ; configure microstepping 16 for with interpolation
    M92 X80.00 Y80.00 Z1600.00 E397                ; set steps per mm
    

    I understand that the detection is 1 in 4 steps. Do I need to fudge the Z estep number to use ustep of 16 to make use of interpoaltion instead of direct as 32 to make better stall detection?

    Hmin- I am getting 84mm/s with my motor at 1/2 the rated current. that seems pretty slow already.
    https://en.smath.com/cloud/worksheet/uNvQ8YSD

    Do I only enable stall detection for the duration when I am trying to pick up the probe? This speed seems quite slow.


  • Moderator

    Why not just use stall detection as the z probe? M558 P10

    Or am I missing something?

    Use x16 with interpolation always. You're not gaining anything but noise by running at x32.

    84mm/s seems slow on the Z axis?



  • @sinned6915 said in Stall detection setup:

    M350 X16 Y16 Z32 E16 I1 ; configure microstepping 16 for with interpolation
    M92 X80.00 Y80.00 Z1600.00 E397 ; set steps per mm

    unless you are using 0.9 steppers for your z axis, your steps are incorrect.
    or are do you have a 2:1 reduction?

    and yes the Duet2 Ethernet can only do interpolation at x16



  • i thought stall detection was useful for conditions where the machine could get hung up, like the nozzle snagging a print.

    i am trying to prevent overtravel on the Z axis past the point of the probe.

    I am not sold on sensorless homing= the thought of purposefully crashing into something to find where it is seems crude to me over a swtich.


  • Moderator

    @sinned6915 said in Stall detection setup:

    i thought stall detection was useful for conditions where the machine could get hung up, like the nozzle snagging a print.

    Yes. Though you're talking about stall detection on the Z axis. Which isn't used very often, though I think it should it work.

    Stall detection on the Z axis is actually a pretty attractive way to home Z. The nozzle is used as the reference point, so no offset, and the stall causes it to snap to a full step, so should have quite good accuracy and repeatability. The downside is that the Z axis design needs to be suitable for stall detection. Preferably natural high steps per mm and rigid enough to cause a reliable stall. There's also the downside that sensitivity can depend on motor temperature.


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