Z motors wont move together



  • Hi guys. Im a new Duet Wifi user and have to say, the learning curve for me is becoming a struggle. Its not overly difficult, but I consider myself more of a hardware guy than a software guy.

    I have designed a beautiful printer and am currently working on getting the beast moving. On the Z, I have 2 Nema 23, turning 2 leadscrews each. They are connected to the same stepper driver on the Duet labeled Z. When I calculate the required ma for the motors (80% max of their rating), I get 2240ma. When I tell the Z to move, it will move one side of the printer, and the other just stutters into oblivion. If I dont reset the board, this would wreck my printer.

    Steppers I am using on the Z axis are the PKP268D28A2 from Oriental Motors. Perhaps, with this basic information, you may be able to tell me if im already wrong with my ma calculations?

    Lastly, as per my intro, I am struggling with the learning curve of the software. I am willing to work with someone and pay for help with firmware configurations so that I can start getting my machine moving. Father of 3 and a full time job does not leave me a load a free time to learn. I can learn well off of a working configuration and make changes to it from there.



  • That seems like a lot of power needed for the Z motors. Well, I guess that if they're NEMA 23s, that's going to need more than the NEMA 17s that most of these printers use.

    The 2 Z motor connectors are set up in series. It is literally impossible to send current to one motor without sending it to both. With the 2 motors in series like this, you calculate your required current for one motor, since the same current goes through both. For that high a current requirement, you may require a 24V power supply. 12V might not be capable of driving enough current to both motors. If the motor coils are higher resistance, 24V might not drive them well either, do you know the rated voltage for the motors? (Lower is fine, since the driver will adjust voltage out to get the required current.)

    If you are using a single extruder, you might be able to use the extra driver to run the second motor. This is the way that I have my printer configured for 2 Z motors. This also allows the software to adjust the motors independently to even them out.

    There's lots of good help available here, I'm sure that you'll be able to get past your learning curve.



  • Im using a 24v power supply for starters. 350W 24V Mean Well for now until final electronics have been figured out.

    Motor details as such:
    Current per Phase - 2.8 A/phase
    Voltage (VDC) - 3.4
    Resistance (Ω/phase) - 1.2
    Inductance (mH/phase) - 4.6

    I thought I had spec'd these motors to the correct size for the board capabilities. Beyond reassigning the 2nd motor to its own driver, should these not work wired in series? For a future config, yes, I would love to drive these seperately. For now, I just want to have the machine move to tweak my hardware.

    Here is a photo of my configuration. IDEX system with the entire print gantry on the Z. I will be getting a Duex5 as soon as I can prove this all works, which it should. Just getting over these firmware hurdles.

    0_1541434319442_IMG_20181016_180518.jpg



  • Motors in series get the same current but half the voltage. That means the maximum speed is lower but at low speed you should get identical torque and with 3.4V motors on 24V you should have plenty of speed.

    Are you sure one axis isn't binding mechanically? Can you turn each motor by hand and feel the same resistance?

    If you are trying to move too fast then one motor will tend to stall and the other run when in series. Have you tried moving very slowly?



  • If I switch the port the motors plug in, the opposite motor will work. Its as if there is a drop in power from one motor to the next. So the first one works well, the next doesnt have enough power. Its not isolated to any particular motor, but the order in which the power cycles through them.

    1 question. If the Duet can handle running at 80% of 2.8A, why does the configurator say the maximum is 2000ma. Am I missing something? Can I put a value of 2240ma? Cause thats what I did.



  • @xandrel said in Z motors wont move together:
    ..............

    1 question. If the Duet can handle running at 80% of 2.8A, why does the configurator say the maximum is 2000ma. Am I missing something? Can I put a value of 2240ma? Cause thats what I did.

    The maximum motor current that the Duet boards used to be able to handle was 2.0 Amps but that specification has fairly recently been increased to 2.4 Amps. https://duet3d.dozuki.com/Wiki/Choosing_and_connecting_stepper_motors

    I'd say that the configuration tool just hasn't been updated.



  • @xandrel said in Z motors wont move together:

    So the first one works well, the next doesnt have enough power. Its not isolated to any particular motor, but the order in which the power cycles through them.

    Sorry but that makes no sense electronically. I think you must have an error in the wiring to the motors. Are you sure each motor is wired to just one of the plugs and you haven't mixed them up somehow?



  • It is actually behaving like one of the sockets is shorted. The motor plugged into that one would not spin but the other would.


  • administrators

    @nophead said in Z motors wont move together:

    It is actually behaving like one of the sockets is shorted. The motor plugged into that one would not spin but the other would.

    I agree. Check that there are no solder bridges between pins of the Z motor connectors on the underside of the Duet. I recall seeing a report of a board with this fault recently. It didn't get picked up during testing because the boards are tested with the 2 jumpers in the Zb position, just as they are shipped.



  • @nophead said in Z motors wont move together:

    It is actually behaving like one of the sockets is shorted. The motor plugged into that one would not spin but the other would.

    @dc42 said in Z motors wont move together:

    I agree. Check that there are no solder bridges between pins of the Z motor connectors on the underside of the Duet. I recall seeing a report of a board with this fault recently. It didn't get picked up during testing because the boards are tested with the 2 jumpers in the Zb position, just as they are shipped.

    I took a quick look at the board this morning, front to back, and cant see anything visual. I inspected the motor wires and connectors and cant see anything wrong. I trust the next step would be to check the pin headers with a meter for shorts?

    Should I be running the motors off their own driver anyways at this point? There seem to be more benefits that way anyway?



  • I have been having a slightly different issue with my z motors, but perhaps it could be related so I'll post here too.

    I have had many a successful print of the printer I built, however sometimes at the end of a print, or after a print has finished and upon starting up a new print, the z-axis motors decide to move out of sync. This seems very weird to me. As I understand it, this should not be possible since both motors are run from the same driver. I have had this issue across 3 different models of the printer shown in this video. All using the Duet Wifi, and two .4A steppers with integrated lead screws fro the z axis. The hardware and duet configuration is identical across all 3 printers. Power cycling the printer always resolves the issue.

    Perhaps the motors are been driven too fast? I know the z motors are in series so this greatly reduces torque over a certain speed.

    Another thought I had was maybe this has something to do with how RRF handles idle currents.

    I also have a single motor with the same specs as the z motor running of another driver on the board, which is used for a multilateral system. I have had no issues with this motor at all.

    [0_1541572296923_IMG_1315.MOV](Uploading 100%)



  • @jckray Video link

    I realized I shared that video for my earlier post incorrectly. This link should work.


  • administrators

    @xandrel said in Z motors wont move together:

    Should I be running the motors off their own driver anyways at this point? There seem to be more benefits that way anyway?

    As they are large motors (Nema 23), I would recommend that. But they should work in series if don't ask for high Z speeds.


 

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