Load/Unload during MM prints ok. Unload end of single material fails  

RE: Load/Unload during MM prints ok. Unload end of single material fails

The filament settings for single and multi-material are different. In expert mode check the advanced options of the filament for multi-material and change those settings in single mode to match.

RE: Load/Unload during MM prints ok. Unload end of single material fails

I am dealing with the same problem. I've tried to customize the single mode filament settings according to the MMU mode settings but they seem to be ignored. At the end of print just some chaotic moves are made resulting in filament uload failure every third print. The printer just stalls with the nozzle heated up waiting for user intervention. Quite unpleasant behaivour especialy when you are not nearby the printer at the moment. The printer even doesn't react on remote commands at this state thus no posibility to turn off the heating remotely (e.g. Octoprint Anywhere).

RE: Load/Unload during MM prints ok. Unload end of single material fails

That's bizarre. Typically single mode can work fine while multi mode will have trouble. For it to be backwards seems weird and anything I can think of (FINDA, filament slipping in the gears, etc..) should be happening in multi mode too.

Does this happen from all the filament paths or just one? When you remove the filament, what does the tip look like compared to how a tip from a multi-tool job looks post extraction?

RE: Load/Unload during MM prints ok. Unload end of single material fails

It has nothing to do with sensors. I use modified variant of them (longer IR sensor arm and magnet below ball for FINDA) and they are very reliable now. The reason of this failure is obvious. It is an ugly filament tip which cannot go through that orange part below the entry of PTFE tube between the extruder and the MMU unit. Filament is unloaded from the extruder and the MMU tries to unload it further but cannot pull it through that narrow path. After the MMU stops dragging I am able to cut the filament in front of the MMU push it back towards the extruder and cut the tip. Then I have to pull some filament from the MMU to cut the ground part. Than after pushing the MMU middle button normal operation is restored and print is finished. 

In MMU mode I have nice cone-shaped filament tips.

So question is, why in MMU mode there are different moves which form nice filament tip while in single mode there are only several quick back and forward moves of an extruder motor which form ugly tips prone to unload error? I've tried to mimic the Filament unload settings from the MMU mode settings to the single mode settings without any effect to those before unload extruder motor moves.

RE: Load/Unload during MM prints ok. Unload end of single material fails

Hi,

I observed the same difficulties even when using S3D. A change of the user end gcode, incl. ramming sequence, was my solution for this issue.

; Filament-specific end gcode
M83 ; extruder relative mode
G92 E0 ; reset extrusion distance
G1 X0 Y210 F7200
; CP TOOLCHANGE UNLOAD
G1 F1600
G1 E0.3085
G1 F1687
G1 E0.3252
G1 F2261
G1 E0.4359
G1 F2904
G1 E0.5599
G1 E-15.0000 F9000
G1 E-24.5000 F5400
G1 E-7.0000 F2700
G1 E-3.5000 F1620
G1 E20.0000 F267
G1 E-20.0000 F283
G1 E20.0000 F299
G1 E-20.0000 F316
G1 E20.0000 F332
G1 E-20.0000 F348
G1 E20.0000 F364
G1 E-20.0000 F380
G1 E20.0000 F397
G1 E-20.0000 F413
G1 E-35.0000 F2000

M702 C

G4 ; wait

RE: Load/Unload during MM prints ok. Unload end of single material fails

I'm having the same issue when using "Original Prusa i3 MK3S MMU2S Single" - see attached picture.  I have to cut the filament at the MMU and pull it out from the extruder door for nearly every "Single" print.  I'd like to say I have great success with MMU2S printing, but that's a different issue.  Is manually changing the Gcode the only fix?

RE: Load/Unload during MM prints ok. Unload end of single material fails

Holger, that worked for me. Thank you for solving this. I guess there is no a way to modify the printing settings accordingly in Prusa Slicer?

RE: Load/Unload during MM prints ok. Unload end of single material fails

I had this problem sometimes but lately it is getting worse. Maybe because of the filament I use or some of the filament is getting old.

Multi color prints work perfect without any load or unload fails. But single filament prints end with the filament getting stuck during unload and the MMU grinding through the filament.

I have now tried the settings that @holger-2 posted and that works for unloading without getting stuck. But as soon as the filament is unloaded the printer loads the next filament to the nozzle and unloads it to load the next. This stops when it comes to an empty channel in the MMU. (I haven't tried it with all filament loaded to see if it goes on in a loop)

I looked it the end G-code but can't figure out why it is dong that.

This is what I have in the "End G-code" in the "Filament settings" in PS 2.4.2

Does anyone know what could be happening here and how fix it. The extra cooling moves seem to do the trick, but I can't see why it is loading the next filament.

; Filament-specific end gcode

M83 ; extruder relative mode
G92 E0 ; reset extrusion distance
G1 X0 Y210 F7200
; CP TOOLCHANGE UNLOAD
G1 F1600
G1 E0.3085
G1 F1687
G1 E0.3252
G1 F2261
G1 E0.4359
G1 F2904
G1 E0.5599
G1 E-15.0000 F9000
G1 E-24.5000 F5400
G1 E-7.0000 F2700
G1 E-3.5000 F1620
G1 E20.0000 F267
G1 E-20.0000 F283
G1 E20.0000 F299
G1 E-20.0000 F316
G1 E20.0000 F332
G1 E-20.0000 F348
G1 E20.0000 F364
G1 E-20.0000 F380
G1 E20.0000 F397
G1 E-20.0000 F413
G1 E-35.0000 F2000

M702 C

G4 ; wait

RE: Load/Unload during MM prints ok. Unload end of single material fails

Based on this thread, I put the following code into my printer's (not filament's) End G-code. I've only done one print, but the tip looked great. When I put the previously posted g-code into the filament's end g-code, I ended up in a loop of loading and unloading filament.

{if max_layer_z < max_print_height}G1 Z{z_offset+min(max_layer_z+10, max_print_height)}{endif} F720 ; Move print head up

; Start comment block of original g-code
;G1 X0 Y210 F7200
;G1 E2 F5000
;G1 E2 F5500
;G1 E2 F6000
;G1 E-15 F5800
;G1 E-20 F5500
;G1 E10 F3000
;G1 E-10 F3100
;G1 E10 F3150
;G1 E-10 F3250
;G1 E10 F3300
; End comment block

; Start custom g-code based on  https://forum.prusa3d.com/forum/original-prusa-i3-mmu2s-mmu2-assembly-and-first-prints-troubleshooting/load-unload-durign-print-fine-unload-at-end-fails/ 
M83 ; extruder relative mode
G92 E0 ; reset extrusion distance
G1 X0 Y210 F7200
; CP TOOLCHANGE UNLOAD
G1 F1600
G1 E0.3085
G1 F1687
G1 E0.3252
G1 F2261
G1 E0.4359
G1 F2904
G1 E0.5599
G1 E-15.0000 F9000
G1 E-24.5000 F5400
G1 E-7.0000 F2700
G1 E-3.5000 F1620
G1 E20.0000 F267
G1 E-20.0000 F283
G1 E20.0000 F299
G1 E-20.0000 F316
G1 E20.0000 F332
G1 E-20.0000 F348
G1 E20.0000 F364
G1 E-20.0000 F380
G1 E20.0000 F397
G1 E-20.0000 F413
G1 E-35.0000 F2000
; End custom g-code

M140 S0 ; turn off heatbed
M107 ; turn off fan
M702 C
G4 ; wait
M221 S100 ; reset flow
M900 K0 ; reset LA
{if print_settings_id=~/.*(DETAIL @MK3|QUALITY @MK3|@0.25 nozzle MK3).*/}M907 E538 ; reset extruder motor current{endif}
M104 S0 ; turn off temperature
M84 ; disable motors

RE: Load/Unload during MM prints ok. Unload end of single material fails

Thanks. I had a quick look at the generated gcode files before and it looked weird. But I didn't have time to test things.

I will try it again with modified printer end gcode and report back.

RE: Load/Unload during MM prints ok. Unload end of single material fails

Thank god I came across this thread! I am absolutely blown away. This thread was started 5 years ago. I just spent $350+ and a week of after-work evenings upgrading to the MK3.5 and the MMU3, and lo and behold, my Prusa setup is still an unwieldy, unreliable piece of crap!!!!!! HOW!?!? How is it possible that 5 years, multiple new printers, a new MMU model, and untold firmware and slicer versions later, this issue has still not been resolved by Prusa? An everyday user can get on the forums and solve everyone's problems with their own ingenious Gcode fix, but Prusa can't be bothered to fix this simple slicer issue? It's truly astonishing. Mind.....blown.

RE: Load/Unload during MM prints ok. Unload end of single material fails

Well, this is an old thread and a short one - which indicates that it is not a very commen issue beeing discussed here (look at the "I found a hardware issue with the MMU logic board" thread to see how a thread dealing with a common issue looks).

My MMU2 works pretty flawlessly without any custom g-code (but with an additional power supply) and mine is not the only one, so you might consider the possibility that you have a different problem or you are one of the very few that have the same issue discussed in this thread.

I would guess that the solution with the modified g-code is only a software work around for a rare hardware problem - like a damaged PTFE for example.