There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
I had an issue where for some reason the selector failed to unload, then moved between two positions while a filament was loaded. Instead of cutting it the filament got bent and lodged between the selector and the body, completely impossible to move. Since the FINDA detects that there is a filament in the tube it refuses to move with the buttons and in the end I had to unscrew the FINDA to lie to the MMU2S, move the selector with the buttons while pulling on the filament with pliers and finally managed to clear the blockage without failing my print.
I think this could have been avoided if there was a way to disable the steppers to safely move the selector by hand. I also almost snagged a finger on a bondtech gear setscrew while troubleshooting, holy moly there's a lot of power behind these motors! There's definitely potential to get yourself hurt by unexpectedly rotating parts.
Ideally I think for the next revision of the MMU2 there should be a interlock microswitch sensing if the lid is open or closed, forcing the steppers to power down when you open it and forcing a recalibration when you close it. It would improve both safety and user experience for not much extra cost in parts.
But I have to say the upgrade from the MMU2 to MMU2S and the latest firmware made a WORLD of difference in reliability. My prints still get interrupted from time to time but it is so much better at handling and recovering from the various error conditions now.
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
Hi Sverre,
The upgrade from MMU2 to MMU2s is definitely a huge step forward in regards to reliability. But it's still far away from being user friendly. What I miss is a clear indicator why something doesn't work. Some information like "Tried to load but no response from IR sensor". Or "FINDA is still engaged, please remove filament from path X" would be very helpful. But I think we are not so far yet. We are at the stage where basic functionality is being improved/stabilized.
In regards to safety features: Yes, sensor would be nice. But I would place this sensor around the box of the printer (which doesn't exist yet 🙂 ). There are many places where you can get hurt. So doing it only for MMU would be kind of half way backed solution.
Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
I think the brains in the MMU2s need a complete lobotomy and replacement. They're too dumb, they need to be able to communicate much more effectively with the RAMBo. The gears need an overhaul, they work against a lot of drag and with certain filaments they just grind the hell out of them and they fail to load. I'm just going over stuff that many people have said already.
I suspect Prusa will release an MMU3 soon. I think the MMU2s works fine in their own hands with their controlled environment, with their filament that is fresh and of certain properties. Out in the wild, the gamut different of filaments make a *huge* difference, with various additives, qualities, diameter uniformity, etc. etc.. Any MMU needs to be able to clever enough to deal with that.
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
I have previously read that the MMU2s feed disabled when the the hotend feed takes over? Wouldn't it be less stress on the filament if the two feeds worked together?
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
I have previously read that the MMU2s feed disabled when the the hotend feed takes over? Wouldn't it be less stress on the filament if the two feeds worked together?
That opens up a whole other can of worms. They must be travelling *perfectly* in sync for that to work; read into the problems with dual-capstan-drive tape decks for a real-world example of the sorts of issues you could expect.
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
Thank you for the response.
Depending on the type and quality of the filament I am using I get significant " slippage " as is. Would having two sets of drive gears be better or worse? It might be nice to have the option written into the gcode.
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
I strongly suspect it will complicate the system significantly and cause many more problems than it solves. If you're having issues with slipping, check your setup and minimize friction, and make sure your tensions for gears are set correctly and that the gears are free of filament dust.
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
You probably right but I might like the option.
Thank you again for your input 😊
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
Depending on the type and quality of the filament I am using I get significant " slippage " as is. Would having two sets of drive gears be better or worse? It might be nice to have the option written into the gcode.
Fix the root cause. Second motor would only make sense if you need to pre-pull from >~5kg roll but even for this case I would rather add a motor to the roll-holder instead of bite hard into the filament.
Current bondtech gears (from both sides) are more then enough for regular friction. If you get slippage right now than it's most likely because the filament is stuck in the extruder. In this case no additional gear will solve it.
Often linked posts:
Going small with MMU2
Real Multi Material
My prints on Instagram
RE: There should be a way to disable the stepper motors in the MMU2S for maintenance during a print
Agreed, there should be a way to disable motors during a print. Would have saved a number of prints I had fail over my use of the mmu2s.
I had an issue where for some reason the selector failed to unload, then moved between two positions while a filament was loaded. Instead of cutting it the filament got bent and lodged between the selector and the body, completely impossible to move. Since the FINDA detects that there is a filament in the tube it refuses to move with the buttons and in the end I had to unscrew the FINDA to lie to the MMU2S, move the selector with the buttons while pulling on the filament with pliers and finally managed to clear the blockage without failing my print.
I think this could have been avoided if there was a way to disable the steppers to safely move the selector by hand. I also almost snagged a finger on a bondtech gear setscrew while troubleshooting, holy moly there's a lot of power behind these motors! There's definitely potential to get yourself hurt by unexpectedly rotating parts.
Ideally I think for the next revision of the MMU2 there should be a interlock microswitch sensing if the lid is open or closed, forcing the steppers to power down when you open it and forcing a recalibration when you close it. It would improve both safety and user experience for not much extra cost in parts.
But I have to say the upgrade from the MMU2 to MMU2S and the latest firmware made a WORLD of difference in reliability. My prints still get interrupted from time to time but it is so much better at handling and recovering from the various error conditions now.