Help with Steps per mm



  • Hi,

    I've a little problem with my steps per mm for the z axis.

    My configuration:
    4 external stepper driver (leadshine dm542eu)
    4 leadscrews 20x5mm
    4 Motors: 1.8° (200 steps per rev)
    Gear Ration: 1.8:1
    (1.8 = 36 teeth (at the leadscrew) / 20 teeth (at the motor))

    Resulting steps per mm: 355.56 at x16 microstepping

    My problem is, that the z axis drives to less.

    For example, when I drive 50mm the printer only move about 30mm.

    I've checked everything 5 times and I don't find the Problem.

    config.g part

    ; Drives
    M569 P0 S1                                                           ; physical drive 0 goes forwards
    M569 P1 S1                                                           ; physical drive 1 goes forwards
    M569 P5 S1 R1 T2.5:2.5:5:0                                           ; physical drive 5 goes forwards
    M569 P3 S1                                                           ; physical drive 3 goes forwards
    M569 P4 S1                                                           ; physical drive 4 goes forwards
    M569 P6 S1 R1 T2.5:2.5:5:0                                           ; physical drive 6 goes forwards
    M569 P7 S1 R1 T2.5:2.5:5:0                                           ; physical drive 7 goes forwards
    M569 P8 S1 R1 T2.5:2.5:5:0                                           ; physical drive 8 goes forwards
    M584 X0 Y1:4 Z5:6:7:8 E3                                             ; set drive mapping
    M350 X64 Y128:128 I0                                                 ; configure microstepping without interpolation
    M350 Z16:16:16:16 E16 I1                                             ; configure microstepping with interpolation
    M92 X286.72 Y204.80:204.80 Z355.56:355.56:355.56:355.56 E420.00      ; set steps per mm
    M566 X900.00 Y900.00:900.00 Z12.00:12.00:12.00:12.00 E120.00         ; set maximum instantaneous speed changes (mm/min)
    M203 X6000.00 Y6000.00:6000.00 Z180.00:180.00:180.00:180.00 E1200.00 ; set maximum speeds (mm/min)
    M201 X500.00 Y500.00:500.00 Z20.00:20.00:20.00:20.00 E250.00         ; set accelerations (mm/s^2)
    M906 X1800 Y1800:1800 Z800:800:800:800 E800 I30                      ; set motor currents (mA) and motor idle factor in per cent
    M84 S30                                                              ; Set idle timeout
    

    Thanks for helping me!



  • @Inno-3D said in Help with Steps per mm:

    dm542eu

    Most important thing - microstepping configuration from config IS NOT passed to dm542eu.
    So question is - how dm542eu is configured ? In case it has 16 microsteps steps/mm then:

    1 screw rotation = 5mm move
    Due to gearing:
    1.8 motor rotation is 5mm move
    1.8 motor rotation is 1.8 * 200 steps * 16 microsteps = 1.8 * 3200steps = 5760steps

    so.. 5760 steps is 5mm, and 1152 steps for 1 mm.



  • @BoA Tahnks for your reply

    So I've to change the 355.56 steps/mm to 1152 steps/mm?



  • @Inno-3D This is what I would do 🙂

    Not sure how this is handled by RRF in case of external driver, but setting microstepping and interpolation for external drivers makes no sense IMO.

    I would change:

    M350 X64 Y128:128 I0                                                 ; configure microstepping without interpolation
    M350 Z16:16:16:16 E16 I1                                             ; configure microstepping with interpolation
    

    into:

    M350 Z1:1:1:1 X64 Y128:128 I0             ; configure microstepping without interpolation
    M350 E16 I1                                             ; configure microstepping with interpolation
    

    and.... set XY to 16 microsteps with interpolation (and change X and Y steps/mm acordingly)

    M350 Z1:1:1:1 I0             ; configure microstepping without interpolation
    M350 X16 Y16:16 E16 I1                                             ; configure microstepping with interpolation
    


  • @BoA
    Tank you very much!!!
    Now it's working!

    I've changed like you said.



  • @Inno-3D Can I ask how Your X and Y axis is driven? They have strange steps/mm also.



  • @BoA

    The x Axis:
    leadscrews 12x25mm
    Motor: 1.8° (200 steps per rev)
    Gear Ration: 1:0.56
    (0.56 = 20 teeth (at the leadscrew) / 36 teeth (at the motor))

    The Y Axis:
    2 leadscrews 14x70mm
    2 Motor: 1.8° (200 steps per rev)
    Gear Ration: 1:0.56
    (0.56 = 20 teeth (at the leadscrew) / 36 teeth (at the motor))



  • @Inno-3D Not sure what is the reson of mounting bigger gear on motor and smaller on screw... seems odd and basically decrease torque available on screw.

    Getting high speeds with screw is always an issue I think better option would be to ger more torque or less current and heat generated by motors.

    I would swap then, so the motors have 20teeth and 36 teeth on screw (higher torque on screw).
    12x25 screw - 12mm diameter and 25mm pitch?
    and 14x70 ?

    In general swapping gears would give You more reasonable steps/mm values, and gear ratio woud be 1:1.8 like for Z

    But this is just my opinion.



  • @BoA Ok, thanks for your opinion, I thought, that less steps/mm are better for the motors, so they are more quiet and don't get so hot.
    But if it's not right, I will change the gears.



  • @Inno-3D It's not the steps/mm that are "hard" on the motors. Steppers draw current even when they are standing still to produce holding torque.

    And with your current setup motor to produce let's say 1Nm on screw needs to make almost 1.8Nm (due to gearing that speeds up rotation but lowers the output torque)

    With gears swapped to make 1Nm on screw, motor needs to make about 0.56Nm (gearing will increase torque, but reduce the speed - which in case of screw drive is limited anyway).

    So with current setup motor needs to work about 3x harder in terms of output torque, which require much higher phase currents and generates heat.


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