Z steppers stall?

  • Hi, I'm replacing Ramp on my printer with DuetWifi, and can't figure out what the problem with the two z motors.
    The motors I'm using on Z axis are these https://www.sparkfun.com/datasheets/Robotics/SM-42BYG011-25.pdf.
    Z motors are installe in series using ZA and ZB, but when I try to move the Z axis, one or both of the motor will get stalled in the middle of the move as shown in the video.

    Here are my setting for now :
    [c]M350 X16 Y16 Z16 E16 I1 ; Configure microstepping with interpolation
    M92 X80 Y80 Z1600 E460 ; Set steps per mm
    M566 X900 Y900 Z3 E300 ; Set maximum instantaneous speed changes (mm/min)
    M203 X12000 Y12000 Z300 E1500 ; Set maximum speeds (mm/min)
    M201 X1000 Y1000 Z5 E10000 ; Set accelerations (mm/s^2)
    M906 X1200 Y1200 Z1800 E1000 I30 ; Set motor currents (mA) and motor idle factor in per cent[/c]

    I also tried lower the Z current down to 300 since that's what the motors are rated for base on the data sheet, but the same problem still occur.
    When I swap one of the Z motor with Y motor, which are much bigger, the Y seems to move in a jerking way, and the torque is close to non exist.
    Almost seems like the two motors on Z driver are interfering each other.
    They works fine if just one of them is connect.
    The only other thing I can think of to try is to lower the Z motor moving speed when using the interface, but I have know clue where to edit that.
    Anyone have any idea about what might be the cause? Thanks!

  • Your Z acceleration seems a bit on the low side…

  • @ShadowX:

    Your Z acceleration seems a bit on the low side…

    Yeah I purposely lowered that down, other wise the motors won't even move 😕

  • JasonW,
    From your information: 0.3 A Z motors, I assume you have very high resistance and impedance motors. If this is the case, i.e. 12v rated motors, you will have very poor performance from them, especially in series. I see you have T8X2 leadscrews, and 1600 steps per mm on this setup. To move at 300 mm/min, the steppers, your motors would have to turn at 2.5 rps. Your motors will already have almost no torque when wired in series at this speed assuming these are high impedance motors. As an example, I have 30 Ohm resistance, and 37mH impedance motors on my machine. They don't run well without 24v power. I will swap them as soon as I can. You could probably use a Y cable fotr the Z motors and use jumpers in the second header to have them run in parallel like on ramps (adjust amperage accordingly). Could a hardware designer commnet on this?

    Also, be careful if you run a 0.3 A motor at 1.8 A, they would probably become burning hot if kept energized.

  • @dcaron:

    From your information: 0.3 A Z motors, I assume you have very high resistance…..

    Thanks dcaron, thats very detailed explanation. I will give the old parallel a try than.

  • Nice looking printer you have there.

    The Sparkfun datasheet for those motors indicates each poll has an inductance of 46mh and 34-ohms of resistance, so these are high-voltage/low current motors and unfortunately unsuitable for use with RepRap type controllers such as the Duet.

    Your X gantry looks pretty heavy, if you have Amazon Prime I recommend these inexpensive high-torque motors. I've used these with the Duet and DuetWiFi controllers and for the price they're hard to beat:


  • Thanks W3DRK, its base on the MendelMax2.0, has been a great learning platform for mechanical design for me.

    Anyway, I just ordered the new motors, should be coming tonight.

    Will come back to report the result.

  • After switching to the new motors W3DRK recommended, everything work as they should now. Thanks a lot for the help!

  • Glad to hear it!

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