gearbox stepper motors on Duet2wifi

  • I have a problem setting up motors with gearboxes
    I have 2 NEMA 17 with 26.85:1 gearbox for XY
    0.067° Step Angle Planetary Gearbox Ratio 26.85:1

    Nema 11 with 100:1 gearbox for my Z axe
    0.018 deg. Step Angle
    NEMA 11 bipolar 4-wire
    Planetary Gearbox Ratio 99.05:1
    Rated current 0.67A & resistance 9.2ohms

    all with
    Lead Screw Diameter: 8mm
    Screw Pitch: 2mm
    Lead: 8mm

    how can I set them up on config
    steps per mm
    max speed change
    max speed
    can anybody help, please?

  • @jarekk I find it's generally best to do the maths for full steps per mm then multiple the result by the desired micro stepping.

    So taking your first example, your (full) step angle is 0.067 degrees. So 1 revolution (360 degrees ) will be 5373.134328 full steps. Now we need to know how much linear travel you get in mm for one revolution. If you use a 20 tooth pulley and 2mm pitch belts (such as GT2) then 1 revolution will equate to 40mm. So your full steps per mm will be (5373.134328/40) 134.3283582. Using 16x micro-stepping which is normal, then the steps per mm become (134.3283582 x 16) =2149.253731.

    If you use 16 tooth pulleys, then one revolution will be 32mm so the steps per mm would be 2586.567164.

    For the Z axis, the step angle is 0.018 degrees which gives 20,000 full steps per revolution. The lead of your screw is 8mm so 1 revolution gives 8mm of linear travel so the (full) steps per mm are 2,500 and at 16x micro stepping this becomes 40,000.

    Your maximum speed will be limited by the step pulse frequency. You need to check because this has recently changed from what I think was 200,000 Hz to 120,000 Hz.

    Assuming it's 120,000, then for X and Y it will be (120,000/2149.253731) = 55.8 mm/second using a 20 tooth pulley or 44.6667 mm/sec using a 16 tooth pulley. For Z it will be 120,000/ 40,000 = 3mm/sec (which is pretty slow).

  • You'll want to use the gear ratios and not the steps angle as they'll give you rounding errors. And you'll want to decide on a compromise between high resolution and high speed before moving on to speeds/jerk/acceleration i think.

    @jarekk said in gearbox stepper motors on Duet2wifi:

    0.067° Step Angle Planetary Gearbox Ratio 26.85:1

    10740 steps/mm (assuming the usual 16 microsteps, unless you need the resolution, you'd probably want less microstepping to increase the speed?)

    0.018 deg. Step Angle Planetary Gearbox Ratio 99.05:1

    39620 steps/mm (again assuming 16 microsteps which is probably not what you want?).

    360  / MotorStepAngle * MotorGearRatio * Microsteps / ScrewLead  
    Motor step angle  1.8     1.8
    Motor gear ratio 99.05   26.85
    Screw lead        8       8
    Microsteps       16      16
    Steps/mm      39620   10740
    Microsteps        4       4
    Steps/mm       9905    2685
    Microsteps        1       1
    Steps/mm       2476.25  671.25

    Edit: The 26.85:1 motor for your X/Y is only rated for 7RPM. With the screw having a 8mm lead thats maximum 56mm/min or 0.93mm/sec regardless of your microstepping and step frequency. Thats pretty high resolution and slow speeds, and would require quite the rigid structure to make sense.

  • @bearer said in gearbox stepper motors on Duet2wifi:

    8mm lead

    Thank you Bearer.

  • @jarekk what are you building that requires such fine stepping in all axes?

  • @mrehorstdmd A high resolution micro printer .

  • @jarekk said in gearbox stepper motors on Duet2wifi:

    A high resolution micro printer

    You may want to lead with that if you have more questions.

  • With the very high resolution your printer's speeds will be limited to a few mm/sec. If the hot nozzle is depositing plastic on top of a previous layer, and moving only a few mm/sec, the nozzle may melt previously deposited plastic, wrecking print quality.

    Have you checked backlash in the gearboxes?

  • @mrehorstdmd thanks Im not going to use plastics nor heated nozzle 🙂