Using sensorless homing with dual motion linear actuator.

  • I'm looking to one of these: with my duet3 system. I picked up three of them at a junk shop and am really exited to have finally found an application for one.
    It is the single stack model and has 1.8 degree steps, essentially two normal nema 17 motors with one connected to a leadscrew.

    I wanted to use sensorless homing because I don't have a need for super high accuracy in this part of my system and it would be a pain to run even more cabling.

    So far everything is hooked up and I have sensorless homing working on the linear axis of the actuator.
    The rotary axis however is proving to be very tough to set up, I think because it has no belt or screw reduction.

    Here are two photos of my setup:


    The idea is that the rotary axis will spin the grey disk with the holes until it hits the rod with the red tape sticking out of the collet as illustrated in picture 2. Having tried almost every combination of feedrate, accel, jerk, current reduction, filtering and stall sensitivity settings, and I cannot get the axis to return to the same point every time. This is probably due to the fact that 1 rotation of the disk= 200 full steps.

    I am thinking that this may just be too much to ask from the stall detection on the duet 3.

    Does anyone have any ideas? I would really prefer not to wire up a limit switch since my controller is 10 feet away from the router.


  • You could put a planetary gearbox on the end of the bottom stepper and shorten the extrusion that houses the lead screw accordingly.
    That would increase your steps per degree, but I'm not sure what resolution you need to get sensor -less homing to be reliable in that instance.

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