Power Failure recovery mess
So I screwed up and had an automation timer kill the power to my printer during 10 hour print - one of my first with an MMU2 (at least of this length). Worst, it was less than 2 hours from completion - let's not cry over spilled filament.
When I got my MK3 (original) back in the days, one of the features I really wanted was the recovery feature from a power failure. Not that it happened that often, it had happened and in 99% of the cases it's due to my stupidity so "important feature". I use OctoPrint but I have the Pi on the same power as the printer sooo - it too lost all tracks. So here I was, with a printer stuck on the model on the bed, as the plastic stiffed around the cooling nozzle. I realized resuming the print was not an option - I saw nothing that indicated what layer/position it was on when the power went out - so reheating the nozzle, removing all "trash" from the bed, cleaning that up, done and I thought "I just need to start the print over", not liking the idea of another 10 hour wait, but it happens. I then did something entirely STUPID - at the time I thought it was what I needed to do. Because the filament was in the extruder when the power was cut, I know the edge of the filament wasn't a nice cut. So I picked the "cut filament" on the printer, and a few lights blinked on the MMU and I thought "that's it, it worked!" (didn't see where the cut filament came out though - first sign of being stupid). After that, all I got was red flashing lights.
Now 6 hours in, I barely got the MMU running again. I had to take it apart, put it back together, pull all the filament out of the MMU, cut off about 30cm of filament and remake the "angle cut" on each filament. I had to take the cartridge off where the filament comes out, where the FINDA sensor is, lost the darn ball doing so (found a spare), double and tripple checked the cutting feature (someone need to post how the filament gets cut in that position - not sure how that's actually supposed to work.
Turns out several things never really got reset after the power-out:
- Filament was still in the MMU cartridge. This prevents the cartridge from moving, but the MMU firmware still THINKS it's move and will happily grab filament and pass it through some space. Figuring out how to release the hold on the filament so you can pull it back out was quite the challenge.
- Soft Reset doesn't seem to do much particular when it's mechanical issues. No feedback at all to what's causing the issues - hence "take it all apart".
- On https://help.prusa3d.com/article/mmu2s-selector-not-moving_1997 the guide completely forgets you cannot remove the wires from the motor. It just sits there hanging! Most of my steppers for other projects/printers have plugs that CAN be removed (not easily but they can). These are fully soldered inside the motor and once broken you need to take the whole motor apart to replace the wires - or as this case shows, letting the motor hang in the wire MAY cause other issues.
- I could hit the right bottom for 2 seconds, the leds would go all the way to position 5, then 4 then go crazy with sounds and then "error lights". I only have filaments in position 1, 4, 5 - the buttons really aren't easy to use. When to long push, when not to, and how to control manual filament selection with NO MARKINGS on the bottoms is a bit of a mystery. Particular to those of us who are just starting down this avenue.
One big question - how do you load filament? I cannot find a way to make this work consistently. And it takes a LONG time to get the filament loaded - particular if you're starting a new roll. The guide says to use a pair of pliers but that must be said in jest - not effective moving a few cm at a time while marking the filament. I use my fingers, still not a lot of room behind the printer but it's easier to get the filament into the tube this way. This doesn't talk about finding new filaments inside the buffer initially - even when you push a few meters in and it comes out on the wrong side, getting it to the right side will bend/crack the filament and that's if you catch it. But most important, getting the filament to catch in the MMU is not easy. Right now I try to do a manual load while pushing the filament and when I feel it being grabbed I know it works. If not it just passes through and I get all kinds of errors (red flashes that means nothing). It's still try-and-error - takes many attempts and in my power-failure case, I removed all filament from the MMU, cut a clean edge and inserted it again.
I've noticed the MMU3 was created partly to deal with some of "my" problems - this may be my option because this will drive me nuts and just cause me to remove the MMU entirely. I hope not, I really have big plans for that thing 😀