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Layer Shift in Y axis - raising Y axis current

Posted by benkitesurfs 
Layer Shift in Y axis - raising Y axis current
January 10, 2021 09:46PM
I am running RRF 3.2_1 on an SKR 1.4 Turbo

My stepper drivers are TMC2208 - set up in spreadcycle mode

I am consistently getting layer shifts in the Y direction. I have reduced my acceleration in the Y direction, and I can continue to do so, but I want to make sure that I am getting maximum torque out of my motor first. The motor is a plain NEMA 17, I don't know anything else about it as it came with my printer long before I modded it beyond recognition.

I started with my amperage set to 1A (M906 Y1000), and wrote a program that just runs the Y back and forth at full rapid for 10 minutes, and I check the temperature of the motor with an IR heat gun right when the program ends. I have now raised the amperage up to 1300 mA, and the temp has not risen over 37˚ C, which seems reasonable to me.

Is it safe to say that the more I raise the amperage, the more torque the motor will generate? I was thinking the motor can tolerate at least 40˚ C - should I keep raising the amperage until I get there?

Any other ideas?

Re: Layer Shift in Y axis - raising Y axis current
January 11, 2021 03:34AM
Motor torque is approximately proportional to current, until the current gets so high that the iron saturates. Most stepper motors are rated to at least 80C. Does the motor have a label on it? If so then you may be able to look up its data online and find its rated current.

Check that you really are running in spreadCycle mode. Layer shifts are far more common in stealthChop mode, because stealthChop reduces torque to the minimum required for normal motion, making the motor unable to handle the sudden increased load when the nozzle hits a blob or overhang.

Another cause of layer shift is setting the corresponding axis acceleration or maximum travel speed too high.

Edited 1 time(s). Last edit at 01/11/2021 03:35AM by dc42.

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].
Re: Layer Shift in Y axis - raising Y axis current
January 11, 2021 11:41PM
Thanks for your reply!

I had previously turned my acceleration and speed down, but that alone didn't solve the problem.

I kept cranking up the current last night, and I settled on 1.45 amps which resulted in a max temp during my test of 52˚ C

I went on to do an 8 hour print with no problems at all! I did measure the motor temp a few hours into the print, and it was 61˚, but it sounds like that's not a big deal. I started another print this morning that has been running for 13 hours now with no issues. Hopefully this issue is solved!
Re: Layer Shift in Y axis - raising Y axis current
January 11, 2021 11:47PM
I am running in spread cycle as well.

My printer is in the garage, so I couldn't give 2 sh!ts about the noise spinning smiley sticking its tongue out Still way quieter than my DRV8825s that I was running
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