Core One MMU3 Filament unloading getting stuck  

RE: Core One MMU3 Filament unloading getting stuck

Everyone who has the problem that the filament is sucked into the gears, read this post until the end. 

Posted by: @alienbliep

I have the same issues.
I think the problem lies in to long unloading of the extruder.
When filament is unloaded i hear the extruder ticking (and possible fipping) the tip of the filament.
The unload is to long and not triggering the filament sensor in nextruder.
I think the cooling tube length setting is the right thing to change if the unload time is based on this.
But i assume mmu rewinding/unloading is only triggered when nextruder filament sensor is deactivated.

Mmu unload should be triggered after the 80mm cooling tube retraction is passed and not look into nextruder filament sensor.

I had the same "fipping" / clicking of the filament tip when the extruder gears hit it during unload. If the ramming before the unloads happens, it does not work correctly, you are left with a string that is then pulled into the gears. I also did not manage to reduce this. However, if you're playing around with the tension, be sure to recalibrate the sensor, which is important.  

I guess the more important thing here is that the ramming phase does what it is designed to do: shape the filament tip. If the tip has no string that can be sucked into the gears, the flipping of the tip is an annoying sound, but can be ignored (at least I currently have no problems with it).

But it would be good to get this fixed as well, since it prevents the filament from being sucked in during stringing. I am curious whether other people, where the C1 works flawlessly, have also experienced these clicks.  Since the hardware is the same, so is the unloading length; this should happen to all users or to none if there is no hardware problem. 

Posted by: @gbmaryland

 

Posted by: @74ck

@gbmaryland, do you use the correct filament profile / add a custom one for filaments with special needs? The blob typically occurs when printing too hot.  For example, I have some PLA that prints best at 195 °C, which is way outside the typical default PLA range around 215 °C --- so when I used the generic profile for that PLA, I also got a blob due to the high temperatures. Try decreasing the nozzle temperature in the slicer by 10 °C for that filament or better, print a temperature tower to find the optimal nozzle temperature. 

I've been sticking with the temp that works best with the print tower for that filament (in this case it was Elegoo Rapid PETG, but I've had issues with PLA and other PETGs too...)

 

I'm really tempted to use explosives at this point. I've got a request to use the high-speed camera...

I know how extremely annoying this problem  😀

When your temperatures are correct, I can recommend running tests as I did to find the problem: I created a minimal G-code file, loaded it into the printer, and started tinkering.

First of all, I would recommend cleaning the extruder gear by disassembling the PG if you have had many unload errors and removing any filament leftovers from the gear.

I appended the G-code here. The g-code does the following:

• It skips all the stuff like bed leveling or homing (because that takes to much time to do various tests)
  • If you want to be on the safe side, uncomment (remove ";")

    ;G28 ; home all without mesh bed level
    

• Heats up the nozzle. Please set the correct temperature for your filament here:

  ; prepare for purge
  M104 S200

• then it loads the filament, purges a bit and then unloads it
• finally it lowers the nozzle temp to 170C to be ready for the next round of testing

During the tests, I adjusted the idler tension, played with the PTFE tube length settings, and checked whether the filament path was frictionless. 
The major problem on my side was my custom filament path (before the MMU) and the wrong-sized PTFE tubes, which caused excessive friction. So I would recommend testing this first. To do so, use a piece of filament ---not directly from a roll---, insert it into the MMU and print my provided gcode. When I've done this, the unload was fine and the filament tip was just perfect. If that's the case, you might have too much friction between the filament roll and the MMU, I would recommend repeating this 3-4 times to make sure it wasn't a lucky one.

If you have an alternative filament path, make sure you use the same PTFE tube size as Prusa does (2.5mm inner diameter) -- I used 2.0mm, which was part of the problem. 

If your hardware setup is fine, then you should not need custom end-gcodes --- this might reduce the symptoms, but does not solve the problem.