autohome fail - z motor thinks 0 is up high, bumps into top
 
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[Solved] autohome fail - z motor thinks 0 is up high, bumps into top  

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Pepe le Vamp
(@pepe-le-vamp)
Trusted Member
autohome fail - z motor thinks 0 is up high, bumps into top

i3 mk3 printer:

Hello. I had a failed print originally from printing too fast (PPE shields), then subsequent errors which indicate Z axis problems, however during my troubleshooting I reflashed the firmware to thew newest version, and now my printer is failing its calibration stuff when it comes to the Z height.

When it goes to auto home, the carriage moves upwards and then just keeps trying to go up and up and up and up. I have to turn it off to avoid damage.
Now if I skip the calibration when i turn it on, it thinks that Z height 0 is actually way way up in the air.

While powered off, I moved the carriage down to the print bed, then turned on & did the wizard calibration: Bed,nozzle,fans, X,Y all pass, but the Z calibration fails and it says to 'check axis'. It doesn't even move.

I know that I can indeed move the Z height up and down a bit using the knob - so physical motor wiring is ok in that regard. I'm just stumped. It thinks 0 is way up in the air.

Posted : 05/04/2020 4:06 am
RH_Dreambox
(@rh_dreambox)
Prominent Member
RE: autohome fail - z motor thinks 0 is up high, bumps into top

Check again that you have used the correct firmware, there are different firmware for MK3 and MK3S.
You may also need to reset the printer before performing a new calibration.

Bear MK3 with Bondtech extruder

Posted : 05/04/2020 1:02 pm
Pepe le Vamp
(@pepe-le-vamp)
Trusted Member
Topic starter answered:
RE: autohome fail - z motor thinks 0 is up high, bumps into top

thanks boss i have done as you said. believe it or not - i initially loaded the mk3s firmware before writing this post - just as you suspected - but the printer is smart enough to warn me it has the wrong firmware loaded. these printers are smart!

ive power cycled this thing many times :/ when it turns on it says in a nice tone that it has not been calibrated. i feel like its in somewhat of a virgin state.

when i do the wizard it is swell until it tries the Z direction. i'm stumped. i feel really guilty because i have this PLA shipped to my house by a supplier at reduced price because of our PPE printing effort, and its just sitting there idle because my printer broke down. i feel bad.

Posted : 06/04/2020 12:59 am
RH_Dreambox
(@rh_dreambox)
Prominent Member
RE: autohome fail - z motor thinks 0 is up high, bumps into top

When it goes to auto home, the carriage moves upwards and then just keeps trying to go up and up and up and up. I have to turn it off to avoid damage.

ive power cycled this thing many times :/ when it turns on it says in a nice tone that it has not been calibrated. i feel like its in somewhat of a virgin state.

No, your printer does not appear to be ready-calibrated. When calibrating the Z axis, the X unit should be transported all the way to the top of the Z axis.
When it reaches the top, you should hear a distinctly noise from the Z motors. That noise indicates that the Z-level upper limit is calibrated. Then the X-unit should be transported down to the bed and the PINDA sensor will then look up the four corner points and calibrate the rectangular shape of the bed. Have you succeeded in this?

Bear MK3 with Bondtech extruder

Posted : 06/04/2020 7:06 am
Pepe le Vamp
(@pepe-le-vamp)
Trusted Member
Topic starter answered:
RE: autohome fail - z motor thinks 0 is up high, bumps into top
Posted by: @rhdreambox
No, your printer does not appear to be ready-calibrated. When calibrating the Z axis, the X unit should be transported all the way to the top of the Z axis.

When it reaches the top, you should hear a distinctly noise from the Z motors. That noise indicates that the Z-level upper limit is calibrated. Then the X-unit should be transported down to the bed and the PINDA sensor will then look up the four corner points and calibrate the rectangular shape of the bed. Have you succeeded in this?

Excellent, we are on the same page now. I appreciate your help.
When calibrating the Z axis, the carriage goes up to the top, and yes it goes BZzzZzzzt as it determines that its at the top. However after some buzzing it will halt at this point, and the display tells me to check the axies.

What do ya make of this?

Posted : 07/04/2020 7:48 am
Pepe le Vamp
(@pepe-le-vamp)
Trusted Member
Topic starter answered:
RE: autohome fail - z motor thinks 0 is up high, bumps into top

Bahaha hey I found a video which explains the fault. He shows how to test the pinda probe by placing metal underneath the pinda probe. He selects in the menu the screen which simply shows you the 0/1 binary output of the pinda probe, and puts the metal underneath it to show its behavior.
You can wiggle the cable & see the pinda probe's malfunction.

I tried the technique here and sure enough, that is exactly my problem. Cable fatigue of the pinda probe. I'm going to repair this & go through all my steps again. Thank you for your help in all this, it is appreciated.

Posted : 07/04/2020 8:23 am
RH_Dreambox
(@rh_dreambox)
Prominent Member
RE: autohome fail - z motor thinks 0 is up high, bumps into top

Good thing you found the error. Cable breakage problems are not always easy to find because the error only occurs in certain situations.
You may report again when you have soldered a new cable.

Bear MK3 with Bondtech extruder

Posted : 07/04/2020 8:53 am
Pepe le Vamp
(@pepe-le-vamp)
Trusted Member
Topic starter answered:
RE: autohome fail - z motor thinks 0 is up high, bumps into top

After repairing the cables I found the true cause of the random pauses, and I would like to put this into the thread for the people from the future.

The machine would simply pause, and the display would go back to the regular idle screen. The PC (printing from USB in Slic3r PE) didn't even know anything had changed. Sometimes I saw a 'rx buffer full' error, but that wasn't always the case. What was it?

There was no serial port errors reported in linux's dmesg. But there was, oddly, messages of my keyboard disconnecting and then reconnecting. I checked what USB hub device it was on, and sure enough - my keyboard shares the same USB hub as my 3d printer.

I do not know if the keyboard is faulty & pulling down the USB port, or the USB port is faulty & pulling down the keyboard & printer - but moving the printer to a different USB controller (not just a different port) has resolved the random pausing issue.

I tried the following things which were not the cause of the random pauses:
Slowing down the printer using the speed knob: in case of serial port buffer full problems. I also sped it up.
It was not the USB cable. Its fine.
It was not the geometry being too sophisticated. I had reduced the model resolution (0.1mm resolution) to simplify geometry-  had no effect.
It was not that I was simply printing from USB & USB is unreliable. It's normally super stable. Something recent had changed.
It was not silent mode. It still randomly paused in normal mode. Nor was it a combination of slient mode & too fast etc. I tried all combinations.
It was not cable fatigue (OK it was also this, but the USB hub problem was real too).

So now my printer is working fine. I hope that whoever has this problem in the future knows to check for errors with their USB hub device. The method I used was seeing the keyboard errors in dmesg, and then using lsusb and lsusb -v to check which port my printer and keyboard were on.

Fin.

Posted : 12/04/2020 6:19 pm
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