Z-axis suddenly going nuts

Knocking sounds and pauses in motion are usually a sign that the driver it overheating and momentarily shutting down. Is the chip hot? It will burn your finger if it is hot enough to shut down.

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[www.hydraraptor.blogspot.com]

Fairly hot, but I can keep my finger on it for 2 seconds or so. This was immediately after powering up, though, so it shouldn't have had much time to heat up. Strangely, it happened less the longer it was running, not more.

Perhaps there is a bad connection in the motor and one coil briefly loses continuity. The only way I can think it can move or vibrate when stationary is if the current changes.

If it isn't the driver and it is specific to one motor, the only thing that can change inside the motor is the continuity of the coils. If it loses contact that would judder the rotor and the vibration could conceivably cause it to make contact again, so it could self oscillate. An intermittent short in one of the coils would make a more subtle torque change, which perhaps fits your symptoms better. Really grasping at straws here.

Try wiggling the wires where they enter the motor while it is stationary and see if you can get it to twitch.

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[www.hydraraptor.blogspot.com]

That's my thought too.. wiggling didn't change anything, but placing the motor in a different spot caused the knocking to disappear (I just moved it over next to the other motor to check if they run in sync).
Unfortunately, my new motors didn't arrive yesterday, but once they do, that will show if it was the motor all along.

I'm so damn DONE with this crap.

I just replaced the stepper motors on Z with the new ones. Wired in serial. All fresh wires, too.
Printed a few tests. Steppers lost some steps and layers shifted, so I adjusted the current etc. Got an okayish print of the Z- cube, some deforming of the X and slight Z-wobble, but the cube is there.
After the print, Z lifts a bit and goes "Wheeee". Literally.
I home okay, try to start another print.. Z goes "WHEEEE" and barely moves, then starts printing at the very top instead of moving down.
Video: [youtu.be]

I replaced the entirety of the Z-axis electronics and the related hardware as well, and it STILL messes up, just in a different way now (sounding different, anyways).

Edit: Ooookay.. apparently that is a seperate issue caused by Cura setting "M203 Z299792458000" at the end of a print for no reason at all.

So, to clarify and conclude: It was a bad stepper motor.

Edited 2 time(s). Last edit at 08/05/2020 06:18PM by Arakon.

Good to hear you got it working in the end.

I don't like the idea of the slicer overriding firmware limits. I prefer the firmware to set the limits to protect the hardware from errant slicer settings.

I still don't understand how it could home correctly at 4mm/s but not jog at the same speed. And a motor that can self oscillate is spooky. I don't think it is easy to see what the fault is as the connections are buried in glue inside.

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[www.hydraraptor.blogspot.com]