Stucked selector, homing keeps failing without any mechanical reason

[KarlZeilhofer]

My selector got stuck during a 2-filament print, and I couldn't find any reason for that.

I tried these without any luck:

• removed cutter blade (even though it looked to sit on the right place)
• filed the selector body a bit, since it rubbed a bit on the MMU body
• greased the spindle and the guiding rods (bad English???)
• Power on reset
• MMU reset

What helped:

• Power Off
• move the selector to the very right end
• Power On

Now the selector is homing correctly again.

Perhaps this is related to https://github.com/prusa3d/Prusa-Firmware/issues/1181

[KarlZeilhofer]

Since the discoveries in #52 it‘s not a real surprise.

[fnordsh]

I noticed that the selector on my MMU2 would not move as easily on the left side. (Most of the time I didn't notice, but especially when homing, it sometimes caused problems.) As it turned out, the steel rods were not 100% parallel. After widening one of the mounting holes, everything works fine, now. I agree the motion control needs to be improved, but maybe this helps until then. YMMV.

[KarlZeilhofer]

@fnordsh Thanks for your hint. Interestingly if I remove the motor spindle, interestingly the selector is moving a bit easier in the left part. So it is exactly the opposite as in your case.