Auto-home does not work for Y-Axis - firmware 3.7.1
Hello,
I assembled my first Prusa i3 MKS yesterday and I'm really happy with it. I upgraded firmware to the latest and I launched Wizard 2 times, each time I got a successfull result, everything is good: perpendicular axis.
I loaded PLA and calibrated the nozzle height, getting best result with filament, running First Layer Calibration many times.
I also printend batrang and prusa logo nicely.
But I noticed sometimes the "Crash detected" error message just before starting to print. (the cycle is always start, crash detected, auto-recalibration of 9 points, starts printing - crash detected produces much noise and i fear that printer will get damage long term because the Y Axis is trying to move beyond its end).
I studied this issue and I found the origin of it, I already google it but I did not find any post so I'm asking help here.
Basically, auto-home is not working for the Y-Axis. Before any print starts (or when I select auto-home from the menu), the X Axis goes to the left, the Z Axis goes down but the Y Axis just moves a little in both directions and sits there. The Y Axis is completely free to move, I oiled the bars too, I can move it nicely from the display (Setting => Move Y Axis - it moves without any problem), and if I manualli move the Y Axis to home (switching off the printer and pushing the bed all over manually) I can print nicely without any crash error. This is just an issue with auto home and it seems to be a software issue, I'm surprised I'm the only one writing about this.
For better undestanding this is an example of what happens:
(1) let's say I start the first layer calibration and stop the printer in the middle, aborting the print.
(2) the X-Y-Z readings are X:139, Y:140, Z:0.2
(3) I push Auto-Home - X Axis moves all to the left, Z goes max down but Y Axis does not move (it moves a little front and back).
(4) next readings are X:0, Y:0, Z:0
so it seems that the software does not move the Y axis but resets axis position to zero, anyway.
This will cause crash errors next time the print starts, because the Y Axis is not aligned.
Thanks
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
If Y is not moving under high acceleration (manual moves use a slower accel) your gear is likely slipping. It's a common build error.
Flat First: Drive gears must be tightened flat-first.
1) Start with both set screws fully loosened so the pulley is free to spin on the motor shaft.
2) Align one set screw dead center with the flat on the motor shaft, slowly tighten the screw until it fully contacts the flat surface.
3) Torque the flat set screw to spec.
4) Now tighten the jam set screw, and torque it to spec.
Once tightened, never touch the flat set screw unless the jam screw is first fully loosened.
Why Flat First? Set screws have flat ends. If you tighten the jam screw first the set screw on the shaft flat doesn't fully contact the shaft, only one small edge of the screw surface is biting. Reversing torques can easily shift the shaft to a position the flat screw no longer contacts the shaft. This lets the jam screw wriggle loose. And after a while, vibration loosens the screws until the gear is free to rotate.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
your gear is likely slipping.
Thanks, I surely will give a try but I do not think this is the case. I printed a full batman helmet perfectly, the Y-Axis moves perfectly during print (under slow and high acceleration). It moves perfectly during the 9-points calibration too, which has the same acceleration of auto-home. It's just Y-Axis that does not want to come home before printing. That's why I suspect a software issue.
I found a similar issue: https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/auto-home-not-returning-correctly/#post-141386
but i do not understand why it should be a mechanical problem (belt too tight, which is not my case anyway). Why, under the same mechanical asset, Y Axis moves for printing and calibration and does not move for auto-home? still a software issue for me.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
When the mechanicals bind, the software detects over current in the motors and records a crash, then it stops movement.
If the same happens in stealth mode, the over current is NOT detected, and you end up with a layer shift in that axis.
And then there's the simple fact AUTOHOME does NOT actually home the printer. It appears to place the PINDA over a heat bed test point. I'm not really sure why Prusa calls it autohome. And it is a rather useless command. I've only used to to see what it does. I have never used it in practice.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
Oh - and if all else fails, and you think your firmware is messed up, try doing a full FACTORY RESET with DATA CLEAR; then run the wizard to recalibrate everything. Glitches have been know to corrupt EEPRON data and cause odd things to happen.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
Thank you, during weekend I will give a try and let you know!
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
I managed to solve the problem adjusting the Y-belt tension, that was too tight.
Apparently the auto-home function tries to home the printer (it tries to find the 0,0,0 coordinates i.e. bottom left down corner), but if belt tensions are too tight (or too loose) it fails.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
I've ran my belt tensions way over the top at 30 lbf when the motor is only rated for 11 lbf and the belt is only rated to 25 lbf ... and it never caused a homing issue. Unless you were bending the motor shaft, there is probably something else going on.
That said, hopefully it won't come back in the middle of the night.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
I also oiled the Y Axis bars, it moves much more smoothly now. I think the firmware was detecting some sort of resistance during the homing function, and now it's gone.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
That resistance is exactly what the TMC drivers are designed to detect as a nozzle crash. Great you found the problem and it's fixed.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
Search for how to do maintenance , clean rods, oil rods with the right oil.
Tighten every bold,
check belts,
Wiggle the extruder, if this is to loose, wiggle bed, etc
etc
Do this every month, if you print a lot.
RE: Auto-home does not work for Y-Axis - firmware 3.7.1
Peter - did you even read the OP post? This is a BRAND NEW PRINTER.