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MMU2S/Idler Motor/Filament pressure issue  

New Member
MMU2S/Idler Motor/Filament pressure issue

Prusa i3 MK3 upgraded to MK3S with MMU2S (firmware 3.10.0-4481)

Multi-colour prints have been working fine, but I'm starting to have problems simply loading and unloading filaments to the FINDA "Load filament->Load filament 2". The issue appears to be related to the downwards pressure on the filament from the idler.  The FINDA sensor is fine but the filament is not being pressed on to the roller even though the idler is roughly in the right position. During the load I can feed the filament by hand in or out but it isn't gripped at all by the idler - the load ends happily (flashing green) once I push the filament far enough in - to the FINDA - the filament is still not being gripped so I retract a little by hand).

Normally when the machine is powered on the 8 stepper motors are powered up and hold their position very firmly. I notice my idler assembly has a lot of 'play' (backlash/slop) in it's rotational position (maybe 10-20 degrees of free-ish movement) and is not held firmly like all the other motors.

Could it be that the idler motor is damaged internally?

Maybe the play/backlash is coming from the idler assembly plastic components rather than inside the motor?  As the idler motor appears to move directly 1:1 without any backlash i.e fully 1:1 in sync with selector motor when it's moving from slot to slot.

Certainly the idler spring-bolts may have been overly tight at some point during the MMU's working life, and occasional sensor trim issues may have resulted in occasional fights between idler and extruder.

Posted : 16/03/2022 1:59 pm
Honorable Member
RE: MMU2S/Idler Motor/Filament pressure issue

I’m having what sounds like similar issues. Yours might be the standard issue of the screws destroying the attachement point to the motor spindle?

I think the inherent design the of the MMU2s is defective.

-It can’t be taken apart and repaired, repairing/replacing he spindle means breaking its holder

-The bottom bolt access with the special ended tool doesn’t really work very well.

-The springs on the idler adjuster I think are too tight and not easily tweaked.

-Once the idler is assembled, it too can’t be taken apart.

On top of all this as far as I saw, you can’t order replacement parts that you need.

Posted : 23/03/2022 6:56 pm