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DarkKnight
(@darkknight)
Eminent Member
Z axis motors warm when idle

My printer has been plugged in and turned on for a few days while I've been doing other projects. I've noticed that the 2 z axis motors are both noticeably warm, while the extruder, X, and Y axis motors are roughly room temperature. They aren't hot, and it doesn't seem to be an operational problem beyond the fact that they seem to be consuming power unnecessarily. The printer isn't moving at all, and hasn't printed in several days. They feel roughly the same temp that they do when they have been printing a while. 

 

Is this expected behavior?

Posted : 07/01/2021 4:29 am
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Z axis motors warm when idle
Posted by: @darkknight

My printer has been plugged in and turned on for a few days while I've been doing other projects. I've noticed that the 2 z axis motors are both noticeably warm, while the extruder, X, and Y axis motors are roughly room temperature. They aren't hot, and it doesn't seem to be an operational problem beyond the fact that they seem to be consuming power unnecessarily. The printer isn't moving at all, and hasn't printed in several days. They feel roughly the same temp that they do when they have been printing a while. 

 

Is this expected behavior?

When the printer is switched on and the steppers are activated, current also flows due to the necessary holding torque. The steppers naturally get warm after prolonged use. But they shouldn't get so warm that you can no longer touch them.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 07/01/2021 10:28 pm
DarkKnight
(@darkknight)
Eminent Member
Topic starter answered:
RE: Z axis motors warm when idle

@karl-herbert

What holding current is necessary for motors that are not moving? No current is required for stepper motors to maintain their position when not in use. The Z axis motors are the least likely axis to move in any given situation where the printer is completely idle. 

Basically, I do not think these should be getting any current at all if you aren’t printing anything or calling for the extruder to move up/down.

The fact that they are warm when idle, indicates they are receiving some amount of power, while also remaining motionless. This is not typically a good thing for the durability of motors, and should be explored if it can’t be explained.

Understand, this isn’t residual warmth after using them. From a completely cold state, if you turn on the printer and do nothing else, they will warm up. They are not hot to the touch, but obviously warmer than ambient. 

Posted : 08/01/2021 12:51 am
JoanTabb
(@joantabb)
Moderator
RE: Z axis motors warm when idle

I believe the Z axis motors are kept powered whilst the printer is turned on, due to the expectation that someone is working on the printer.
It is believed to be possible that the application of effort to the extruder, for instance could cause one side, or the other side of the Z axis to sag and put the X axis out of calibration relative to the z axis,   (in My experience, this was discussed when the Mk1 printer had 5mm/ 0.8mm pitch leadscrew set up (About six years ago), Now that the Mk3 has an 8mm pitch, mis alignment of the X axis is even more likely if the motors are not powered).
an alternative option would be to drive the Z axis to the top, at the beginning of every print to ensure that the X axis was perpendicular to the  Z axis. I understand Prusa's experience showed that leaving the Z motors powered at a low holding level was found to be preferable to the driving of the z motors until they stalled against the Z end stops, before every print. 

this issue has been explored by the Prusa developers and the decision made, that by design intent the Z motors will remain powered whilst the printer is ready for service in the powered on status. 

there is nothing to stop the user turning the power off to achieve a lower idle status current consumption, such an action would also remove the quiescent current caused by the power supply idling for extended periods.

Yes I know the x axis may sag whilst the power is turned off....   this is one of the reasons why the later firmwares monitor the variance of bed levelling offset at the beginning of every print during the Mesh Bed levelling process and if more variance than expected, is monitored, Z axis calibration is enforced.  

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 08/01/2021 2:34 am
karl-herbert
(@karl-herbert)
Illustrious Member
RE: Z axis motors warm when idle

@darkknight

A machine operated with stepper motors must always supply the steppers with power in the initialized state (holding torque) so that they do not lose their position. It is not relevant whether the CNC machine processes a gcode or not. If, for example, the motors were de-energized after referencing the axes, they could lose their position due to external forces. Of course you can influence this holding current (firmware), or switch it off after a certain time (#define STEPPER_INACTIVE_TIME). Marlin also provides a gcode to disable the steppers (M84).
But how Prusa has solved this exactly, you can find out best at Prusa itself.

Statt zu klagen, dass wir nicht alles haben, was wir wollen, sollten wir lieber dankbar sein, dass wir nicht alles bekommen, was wir verdienen.

Posted : 08/01/2021 8:01 am
muddymaker
(@muddymaker)
Trusted Member
RE: Z axis motors warm when idle

Unless you are using the LCD screen for a night light and you are not printing with it, I would suggest you turn it off. It's a rocker switch on the side of the PSU if it's the silver PSU and if you have the black PSU it's on the rear.

Posted : 08/01/2021 10:30 am
DarkKnight
(@darkknight)
Eminent Member
Topic starter answered:
RE: Z axis motors warm when idle

Thank you everyone, particularly @joantabb, for the informed responses. I’m not sure ramming the Z axis to the very top would consistently produce a reliable result due to assembly & part errors. Another approach would be to create fixed points on each side of the frame that the top of the extruder itself can forcibly contact, then have the firmware use those as detectable end stops for fixing alignment. Probably more reliable than depending on the axis screws to not dig into the top mounts over time.

After looking at how else it might be done more elegantly, it’s clear it would require some kind of hardware support which isn’t present in the current motherboard. This seems like a good area for improvement in later models. Dual accelerometers, one each in the frame and the extruder detecting level relative to each other would probably get it done inexpensively & reliably after some initial calibration. An extruder mounted accelerometer seems like a useful innovation for proving jitter feedback and detecting print errors when the actual extruder movement doesn’t match expected movement. Maybe some more advanced development here can provide a higher level of calibration using the accelerometer to make small adjustments in realtime to where the extruder is to correct for slop in the X & Z axis, improving accuracy on fine details. Klipper if I understand it correctly, I think does something like this, but just using mathematical models instead of realtime measurements. Seems like a cool development if you ask me, though it’s all just daydreaming at this point I suppose. 

 

@muddymaker

I do keep it off most of the time, but as it’s a relatively new build, I’ve been spending a lot of time working on Octoprint, and doing research while working out problems with printing PETG. Since the RPI with octoprint is powered from the printers 24v supply, I keep the entire assembly on when working on the OS and camera. Will probably eventually setup a system to allow octoprint to power on and off the printer without needing to switch the supply manually. 

 

Posted : 08/01/2021 7:12 pm
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