Delta layer shift problems



  • Hi,

    I've been working on my custom mini-delta trying to get the best performance I can.

    I have been using Simplify3D (S3D) for slicing with a printing speed of 90mm/s which I think was the default speed provided by S3D.

    My initial tests consisted of typical objects like 25 mm cubes and such. I also used some 5mm thick disc objects to verify printing over the entire diameter.

    All of those worked well.

    But then I tried to print some squares of increasing size. 20x20x10 and 30x30x10 printed just fine. But a 40x40x10 object exhibited significant (and unacceptable) layer shifting.

    So as a test I dropped the speed in S3D to 30mm/s. Now larger objects (40x40x10, 60x60,x10) printed fine as well.

    So I THINK that tells me that I need to make some settings in firmware but I haven't a clue what those settings might be.

    If needs be I will simply accept the speed limit but I hope perhaps I can do better than 30mm/s.

    Does anyone have any suggestions as to how I should proceed?

    Thanks much.

    Frederick


  • administrators

    Need more information. Which Duet are you using, what is the specification of the motors, and what VIN voltage are you using? What are your config.g settings?



  • Hi,

    Thanks for the feedback.

    Here are what I think are the essential parts from config.g - the complete file is attached:

    0_1551639250172_MK_1 config.g

    G21
    G90
    M83

    M669 K3

    M584 X0 Y1 Z2 E5

    M569 P0 S1
    M569 P1 S1
    M569 P2 S1
    M569 P3 S1
    M569 P4 S1
    M569 P5 S0
    M569 P6 S0
    M569 P7 S0
    M569 P8 S0
    M569 P9 S0

    M84 S30

    M92 X100 Y100 Z100
    M906 X1000 Y1000 Z1000 I30
    M203 X18000 Y18000 Z18000
    M201 X1000 Y1000 Z1000
    M566 X600 Y600 Z600

    The system is running on 12 volts.

    The stepper motors are these:

    https://www.omc-stepperonline.com/nema-17-bipolar-18deg-45ncm-64ozin-168a-28v-42x42x48mm-4-wires-17hs19-1684s1.html

    Thanks for the assistance.

    Frederick


  • administrators

    You haven't said which Duet it is, so I will assume a Duet WiFi or Duet Ethernet. The Maestro has additional considerations because of its different drivers.

    Skipped steps usually occur on travel moves. I calculate that with those motors and a 12V supply, for some moves the torque will start to drop when the speed exceeds about 105mm/sec. You have set the maximum speed to 200mm/sec in your M203 command. So I suggest you reduce the maximum speed.

    You could also try increasing the XYZ motor current to 1100 or 1200mA, if that doesn't make the motors run too hot.



  • @dc42 Thanks for the feedback.

    I will do some tests and see what happens.

    Do the settings for acceleration or "jerk" have any effect on layer shifting issues?

    Frederick


  • administrators

    @fcwilt said in Delta layer shift problems:

    Do the settings for acceleration or "jerk" have any effect on layer shifting issues?

    Yes they can do. But your acceleration and jerk settings are quite modest - unless the slicer you are using overrides them, as some slicers do.



  • @dc42 said in Delta layer shift problems:

    @fcwilt said in Delta layer shift problems:

    Do the settings for acceleration or "jerk" have any effect on layer shifting issues?

    Yes they can do. But your acceleration and jerk settings are quite modest - unless the slicer you are using overrides them, as some slicers do.

    Hi,

    Well I set my max speed in config.g to 100mm/s and that seems to have solved the problem - and I was able to restore the printing speed in the slicer to 90mm/s

    Can you direct me to a resource that would show me how to compute stepper motor torque?

    Thanks again.

    Frederick


  • administrators

    @fcwilt said in Delta layer shift problems:

    Can you direct me to a resource that would show me how to compute stepper motor torque?

    There is a motor EMF calculator at https://reprapfirmware.org/, however it's giving the wrong inductive back EMF for your motor. We will get that fixed. Meanwhile, use this spreadsheet.

    0_1551699368374_StepperMotor.ods



  • @dc42 Thanks much!

    Frederick


 

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