MMU3 filament manipulation operations REALLY need a cancel button  

MMU3 filament manipulation operations REALLY need a cancel button

Printer: Core ONE

Printer Firmware: 6.5.3+12780

MMU3 Firmware: 3.0.4

Sometimes when I try to load filament into the MM3, things don't quite line up correctly. Sometimes the filament can't quite bridge the gap from tube to tube over the pulley gears in the right spot. Most commonly, the filament tip is bent and it misses the hole to the selector gets pushed out of the MMU entirely. I've also had it just catch on the hole to the selector and get ground away between the pulley gear and idler. Either way, the filament does not reach the sensor in the selector and so the pulley just keeps running and running and there is no button on the screen to stop it. I've had to pull out the PTFE tube from the selector and shove a piece of filament in to trigger the sensor. That works okay if I'm just loading new filament to the MMU, but I've had it happen in the middle of multi-material prints too and failed to get everything back in place before the MMU tried advancing the next filament, which forced me to scuttle the print.

Once I had an issue retracting a filament from the print head to the MMU, where it jammed in the extruder gear. The pulley gear just kept grinding it away until it broke while I scrambled to get it unjammed. 

I also had an intermittent issue for a long time that was caused by a poorly calibrated filament sensor on the MMU (my fault), which would occasionally cause the MMU to think it had finished retracting a filament when it had not, and then try to move the selector with filament still in it. That was a huge pain to clean up, in part because when I tried to retry retracting the filament, the selector carriage would try to re-home first while filament was still stuck in it.

The point is, sometimes shit happens. Right now, there is no software contingency for dealing with it. When the MMU is loading or unloading or switching filament (even when it's a user-initiated operation and not part of a print), there's no way to just tell it to stop from the printer screen. There's no button to cancel the operation, or to go back to the home screen so you can go to the Control menu and disable the motors. You have to do dumb hacky things like pull out PTFE tubes and jam filament into sensors, and then do more dumb hacky things to clean up the situation afterward. Or hit the reset button and kill whatever you were trying to accomplish at the time.

Please please please please please add cancel buttons to at least the MMU filament loading and unloading screens. Preferably they would be added to any MMU operation screen that doesn't have them. I don't know what kind of complexity that means adding to the state machine behind those operations. Maybe there isn't a good recovery path once the operation is paused in an unknown state. But something is still better than nothing.