Random missed steps

  • Hoping this is the right category to post this thread,

    To all,

    I finally got my Kossel Mini printing!

    Well…sort of...

    Back in August I purchased this cheap kit: https://www.3dprintersonlinestore.com/flsun-3d-kossel-delta-diy-kit

    Not necessarily from that site, not necessarily from the same site, however the same kit all the same.

    I am an Electrical Engineering and Computer Science student, but motors; controllers; robotics; programming; and 3D printing is all relatively new to me (within the past year). I have learned a lot, by no means am I proficient with any of it. If anything, I try to do my research before I spend my money.

    Failure after failure, I have replaced what did not meet my standards, starting with a $200 delta, I've been through a lot of failures.

    The carbon rods are new, the effector is a an aluminum effector from Robotdigg, the extruder is an E3D V6 Hot end with a (nickel plated) copper heater block and (nickel plated) copper nozzle with a 0.4 mm bore with a PT100 Thermocouple and the daughterboard. The controller is the Duet Wifi with dc42's 1.17d firmware. I also have the ir sensor for it. The printer is powered by 12v through my previous computer's ThermalTake 600W power supply with the green and ground wire shorted with a jumper.

    At, what seems to be, random times the motors begin to skip, then skip some more…then go haywire and the printer goes nuts. Whatever my programmed travel speed is, it goes full speed in a different direction each time. This has happened while homing the printer, during calibrations, at the beginning of a print, and has even been fine until an hour and a half into a print then goes haywire.

    My first thought was a bug in the firmware (my thought was that I fiddled with something and accidentally corrupted the firmware), and even after (completely erasing and) re-flashing multiple different versions, it still is unpredictable.

    It is not until today that I have come up with a new theory about the issue. The nema 17 motors are from the cheap kit, probably about 30-40 mm motors. I have rather high speeds because I know everything is tight, and low enough friction to work perfectly and could probably speed it up as it still being developed.

    I have put off running it at 24v because I know I know nothing about power supplies, and procrastination is a curse. I do have fans and a hot end heater designed for 24v, unsure if I must rewire the heated bed.

    Is my problem most likely the lack of torque in the motors? Is it possible the jump to 24v could solve my problems? Or is the problem more likely the quality of the motors themselves???

    What should I do?

    Thank you in advance,

  • administrators

    Is there a model number attached to the motors, that would allow you to look up the motor data? If not, measure the size of the motor and the resistance of one of the windings. We can then compare it with data for similar motors.

    What motor current do you have selected in your M906 command?

  • Thank you David, I greatly appreciate such a quick response.

    The motors are all SL42STH40-1684A with a link to the datasheet here:

    Resistance/Phase: 1.65Ω
    Current/Phase: 1.68A
    (both phases^)
    Inductance/Phase: 3.2mH
    Rated Voltage: 2.8V

    This is the whole line from my config.g
    M906 X1000 Y1000 Z1000 E500 I20 ; Set motor currents (mA) and increase idle current to 60%
    ….Which looks like I20 should be I60.

    It just dawned on me that I never did that calculation. Is it really that simple?

  • administrators

    Your motor currents look ok to me.

    Next time it gets into that state, please try moving the motors individually like this. Send G91 to select relative mode. Then send G1 S2 X10 F1000. That should move the X carriage up 10mm. You can replace X10 in that command by X-10 to move the X carriage down 10mm, or Y10 to move the Y carriage up, and so on.

  • What I mistook for missed steps was actually just a loss of torque. It turns out my travel speeds and acceleration speeds were a bit ambitious! Thank you for the help!

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