Dual Z axis steppers moving at different rates

Hi, I'm doing some testing with my printer and after a little while the z axis becomes askew, one side always ends up higher than the other. Is there anything I can do to fix this?

About the only way that can happen that I could think of is that one of the sides is binding causing motor stalling and lost steps. Try moving the axis up and down by large amounts (10 cm or more) manually and see if you can observe either motor stalling due to binding. Do it at various speeds.

The two sides of the axis need to be exactly parallel to one another - including both the smooth bars and the threaded rods. Also the motor shaft, threaded rod, and nut in your X end need have coincident centers; likewise your smooth bars and bearings.

It's also quite likely that you don't have enough current through your Z stepper motors. The two Z motor connectors are wired in parallel, which is the wrong choice - the motors used in most RepRaps are better connected in series (yet another limitation of the Arduino/RAMPS combo). The current provided by the drivers is split between the two motors. You could try turning up the Z motor current, as long as the driver chip stays cool enough.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

If he had a spare stepper driver, how difficult would it be to run it in parallel with the existing Z stepper? Would it be just a matter of running jumpers from the input of the Z stepper to the spare, or would he have to cut tracks? Or worse?

Quote
frankvdh
If he had a spare stepper driver, how difficult would it be to run it in parallel with the existing Z stepper? Would it be just a matter of running jumpers from the input of the Z stepper to the spare, or would he have to cut tracks? Or worse?

RAMPS has a socket for a 5th driver, and I think Marlin can be configured to drive it in parallel with the Z stepper. So no modifications needed. Or he can wire the 2 motors in series. But he should check for binding and see if the current can be turned up first.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].