2nd Filament fails to reach extruder after bowden length calibration  

Re: 2nd Filament fails to reach extruder after bowden length calibration

Hi Yan Ling, check the diameter of the hobbed section of all five MMUv2 drive wheels, they may be different if filament 1 drive wheel is bigger than filament 2 drive wheel, you may have found your problem. if there are differences, re assemble your MMU with the smallest diameter drive wheel in position for filament one... with the larger drive wheels in the remaining 4 filament positions

then re do the calibration on filament 1 and the remaining filaments should feed slightly further, which should be resolved on the purge area

regards Joan

Re: 2nd Filament fails to reach extruder after bowden length calibration

Thanks Joan!

Just a clarification - would the drive wheels you are referring to be the big smooth ones that are held by individual shafts, or the toothed ones held by a long central shaft?

Re: 2nd Filament fails to reach extruder after bowden length calibration

Joan, thank you!

Your diagnosis was spot on, I have exactly the same problem as Yan Liang, and had the bad luck of installing one of the largest gears on position 1.

my gears measure 6.25, 5.89, 6.11, 6.26, 6.27 . which at 360mm travel to the extruder tube makes for a difference of 21mm (!) .

Does the system support per-gear calibration? I worry that such a big discrepancy will grind the filament if I calibrate for the smallest gear...

Need to ask support what are the tolerances for the gears...

Re: 2nd Filament fails to reach extruder after bowden length calibration

Good morning Bozo, I am pleased that this information helped.

Yan Ling,

I am talking about the drive wheels on the motor shaft

measure at the hobbed cut away point, and sort smallest diameter to largest diameter, then install with the smallest diameter in filament one, position, so that when you configure the feed distance on filament one, it will feed the correct distance, m and other filaments may feed more...mm the excess will be purged into the waste areas.
regards Joan

Re: 2nd Filament fails to reach extruder after bowden length calibration

Talked to the support, really nice chaps. My hobbed gears are out of spec, I'll be getting a new set.

The nominal diameter for the gears is about 6.2.

I'll try installing the three 'good' ones in positions 1, 2, 3 for now to have at least a PMMU (P for partial) 😛

I also created https://github.com/prusa3d/Prusa-Firmware/issues/1194 with an idea how to automate the calibration.

Re: 2nd Filament fails to reach extruder after bowden length calibration

I put a note on that paragraph in the online build manual suggesting folk measure and sort the hobbed wheels putting the smallest one on filament one!,
regards Joan

Re: 2nd Filament fails to reach extruder after bowden length calibration

Thanks Joan! Print seems to work fine now on 1st and 2nd filament after swapping. It also makes sense now that my 1st and 2nd wheel has a 0.4 mm diameter difference! 😯

My wheel diameters:

1: 6.30mm
2: 5.92mm
3: 6.27mm
4: 6.15mm
5: 6.25mm

Bozo - Does it mean I should approach support as well?

Re: 2nd Filament fails to reach extruder after bowden length calibration

Does it mean I should approach support as well?

If you can wait a few days, then there should be new firmware available which will allow you to calibrate each filament feed.

Peter

Re: 2nd Filament fails to reach extruder after bowden length calibration

that should be a good change

Re: 2nd Filament fails to reach extruder after bowden length calibration

Oh my word, I just found this... thankful that I’m not the only one with this issue. J spent the last 3 days checking everything and changing the placement of the spools.

@pjr do you know when the fix will be out? Is there an issue on github already for tracking?

Also if I were to do it the mechanical way, would that mean taking the whole MMU apart?

Re: 2nd Filament fails to reach extruder after bowden length calibration

think it's just getting the gears out, measuring them, putting them back smallest to biggest. that might be the whole thing just to get to them, not sure I don't have mine yet 🙁

kinda looks like, if you can get to the screws holding the gear motor your home free

Re: 2nd Filament fails to reach extruder after bowden length calibration

Also if I were to do it the mechanical way, would that mean taking the whole MMU apart?

It's quite easy to do, actually, you don't even have to take it off the printer.
[*] remove all filament from the mmu2
[*] cut more or less all the zipties on the mmu (you can keep the one on selector motor), unplug the gear feed motor, the safety latch is on the 'inside' so you'll probably need to unscrew the electronics
[*] unscrew the idler tensioner and open the idler
[*] unscrew all 4 bolts of the feed motor and pull the motor out
[*] shuffle pulleys and reverse the steps 🙂

The second time (sigh) went pretty fast. 🙂

Re: 2nd Filament fails to reach extruder after bowden length calibration

@pjr do you know when the fix will be out?

All I know is that it was requested back end of last week. But there is also some other stuff to be done at the same time and there's testing. I would hope this will be resolved soon.

Swapping the pulleys is not a great work-around; you end up pushing the filament into the Bondtech which caould cause skipping at the MMU and result in filament damage - which could lead to skipped layers later in the print 🙁

Peter

Re: 2nd Filament fails to reach extruder after bowden length calibration

All I know is that it was requested back end of last week. But there is also some other stuff to be done at the same time and there's testing. I would hope this will be resolved soon.

Would it create a lot of process/communication overhead if such requests would get recorded as an issue in the public repo. That would make such issues more easily discoverable...

Swapping the pulleys is not a great work-around; you end up pushing the filament into the Bondtech which caould cause skipping at the MMU and result in filament damage - which could lead to skipped layers later in the print 🙁

It's far from perfect. There is indeed some grinding going on, but I have already two sucessfull prints under my belt (gecko and sheep) whereas before the swap I could not get any color change to work (due to bad luck of randomly selecting the biggest pulley for no.1)
The gecko was flawless. the sheep I had exactly one retract issue (filament jammed when mmu was pulling it out, luckily it was the last retract at the end of print, I still need to learn how to resolve those)

Re: 2nd Filament fails to reach extruder after bowden length calibration

@pjr do you know when the fix will be out?

All I know is that it was requested back end of last week. But there is also some other stuff to be done at the same time and there's testing. I would hope this will be resolved soon.

Swapping the pulleys is not a great work-around; you end up pushing the filament into the Bondtech which caould cause skipping at the MMU and result in filament damage - which could lead to skipped layers later in the print 🙁

Peter

I picked the gear just smaller than average, so that I wouldn't ram TOO much, but still get most of them there. With ~40cm in the bowden tube, you can figure out how short you'll be, I'm something like 1 cm now, I was 2.5. I could get it lower but I'd start ramming 4 cm extra into the machine.

Re: 2nd Filament fails to reach extruder after bowden length calibration

Would it create a lot of process/communication overhead if such requests would get recorded as an issue in the public repo. That would make such issues more easily discoverable...

This is something that is being worked on in-house and in conjunction with beta-testing, but if you wish you can raise an issue on Github.

It's far from perfect. There is indeed some grinding going on...

And that's why I suggested moving the pulleys around - it's simply a temporary work-around; I could have released my fix for the problem, but then I would have become "responsible" for the problems we are experiencing. I would much rather wait for the official solution.

Peter

Re: 2nd Filament fails to reach extruder after bowden length calibration

I picked the gear just smaller than average, so that I wouldn't ram TOO much, but still get most of them there. With ~40cm in the bowden tube, you can figure out how short you'll be, I'm something like 1 cm now, I was 2.5. I could get it lower but I'd start ramming 4 cm extra into the machine.

Yeah, that should be OK. The MMU currently feeds 20mm with the Bondtechs turning at the same time, but the problem is the speed matching when the filament is late arriving. (actually, speed-matching is currently an issue at the moment anyways 🙁 )

Peter

Re: 2nd Filament fails to reach extruder after bowden length calibration

Ah, I'm glad I found this - this might be exactly the problem I'm having right now. I'll check the calibration and the hobbed wheels when I get home. Thank you!

And, this might be a dumb question, but...
Why is there a need for a bowden length calibration when we have a filament sensor in the extruder?

Re: 2nd Filament fails to reach extruder after bowden length calibration

Ah, I'm glad I found this - this might be exactly the problem I'm having right now. I'll check the calibration and the hobbed wheels when I get home. Thank you!

And, this might be a dumb question, but...
Why is there a need for a bowden length calibration when we have a filament sensor in the extruder?

As it is, in its current implementation, I understand that it is not closed loop between the filament sensor and the pulley