Losing steps with Nema 23 and 24V in a Duet wifi



  • Hello

    I am building a large format Cartesian printer controlled by a WiFi duet at 12V input and in my initial design the Y axis was driven in the middle of the axis by a Nema 17 of 1.7A, the problem was that it had too much vibration since the ends were not held. Then I decided to remove the Nema 17 and attach a Nema 23 of 2.8A (57STH56-2804A8) at each end to gain more speed and decrease the vibration, additionally I changed the 12V (20A) source to one of 24V (15A) because in theory it is better 24V.

    When I had the Nema 17 installed I could reach 3600 mm / min to 1200 (mA) without problem and without losing steps, although with enough vibration, the problem now is that with the Nema 23 I can not exceed 2100 mm / min because during the print start to lose steps, I have tried more than 2000 mA but both engines are heated considerably and continue to lose steps. I have tried connecting them in series to the same driver and also with independent drivers without any improvement.

    I am truly worried and surprised because I do not understand how a single Nema 17 works better than two Nema 23 at the same time and moving the same load. Finally I tried changing the two Nema 23 for two Nema 17 and finally I was able to print without losing steps, but with maximum speed of 1600 mm / min and maximum acceleration of 50mm / s ^ 2, I investigated and saw that the tb6600 driver can be used , But I'm not sure.

    Mechanically I do not think I have any problem since I am using ball screws, so the system is very smooth, although with a bit of inertia.

    0_1551929266865_image.jpg

    I appreciate that someone can help me, regards



  • There is a stepper motor calculator that can be found at https://daycounter.com/Calculators/Stepper-Motor-Calculator.phtml if you fill in all the information you will get a theoretical max speed that you can drive the motor. I did a simple check using information provided for stepper motors from (stepperonline.com) using the following motors (nema 17 17HS16-2004D 45Ncm) and (nema 23 23HS20-2004S 90Ncm) you will see that the calculator outputs the results Nema 17 max speed max speed 11.6rev sec and the nema 23 max speed 6 rev sec. It is not just the inertia but also the induction that plays with the max speed a stepper can move. If for example you were to change the induction on the Nema 17 motor from 2.6mh to 5mh you will see that the Nema 17 motor would now only have a max speed of 6 rev sec. I hope this helps a bit


  • administrators

    That stepper motor calculator only tells half the story. It calculates the effect of inductance, but not the effect of back emf due to rotation of the motor. The calculator we provide at https://reprapfirmware.org/ calculates both.



  • You might find this calculator useful as well. https://forum.duet3d.com/topic/6853/maximum-acceleration-calculator


 

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