Intermittent Rear Z-Motor Failure at Startup - Core One+
Hi everyone,
We're experiencing an intermittent issue with our Prusa Core One+ and could really use some ideas on what to check next.
Problem Description
The rear Z-axis motor occasionally fails to "wake up" correctly during startup, causing the bed to tilt dramatically as the two front motors move normally while the rear stays locked.
(see video ).
Symptoms & Pattern
- Timing: Only occurs immediately after powering on the printer, only first use of the day
- Intermittent: Doesn't happen every time, but when it does, it's always at startup
- Once past startup: If the printer starts successfully, it runs flawlessly all day without issues
- Temperature: Printer is in an unheated room (~15°C ambient)
What We've Checked
- Cable routing and connections - everything appears secure
- Physical obstructions - nothing seems to be blocking movement
- The dust cover is visible in photos, but we verified it's not interfering (plus the issue occurred frequently before installation)
Any known cold-start issues with Core One+ motors?
We're running out of ideas and would really appreciate any suggestions from the community.
Thanks in advance!
RE: Intermittent Rear Z-Motor Failure at Startup - Core One+
The common suggestion here is to do the following:
Lower the bed to the bottom.
Loosen the screws holding the trapezoid nuts on those z-axis screws.
Move the bed up and then back down.
Tighten the screws on the trapezoid nuts - not too tight, as you don't want to deform the nuts.
Also consider lightly lubing the z-axis screws using the Prusa lube.
RE: Intermittent Rear Z-Motor Failure at Startup - Core One+
I have similar but it's always the back and right that doesn't work.
Always happens on power up the same as you.
Happens even when selecting Preheat, only the left side of the bed goes down.
If using the control to move the access it seems to continue to do it until you move the axis back to 0mm then they all start working in sync again (see video)
If I know others are experiencing this I'll raise an issue on GitHub. I thought I was the only one.
RE: Intermittent Rear Z-Motor Failure at Startup - Core One+
The Z-axis motors are connected in parallel. It is impossible for them to move independently, which means that something is inhibiting the motors that aren't working. The common cause is that there's too much friction. That can happen because the trapezoid nuts are overtightened, they're improperly aligned, they're mis-shaped and adding too much friction, etc. That's why the earlier suggestion to loosen the screws holding those then gently retighten them.
I'd get onto a chat with Prusa support if that doesn't help you.
RE: Intermittent Rear Z-Motor Failure at Startup - Core One+
Thanks, I will try these steps today.
I can't work out why there is no stalling type noises on the other two motors? Once the working motors gets to a certain point it stalls and makes a very loud not happy noise.
I feel like I can replicate the issue, so I will report back in the next days if this fixes the issue for me.
RE: Intermittent Rear Z-Motor Failure at Startup - Core One+
Many users have reported very tight trapezoidal nuts due to poor manufacturing tolerances. I think this is most likely to be your problem. Lubrication might help, but it won't solve this problem.