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MMU2 Gets Confused About Selector Bearing Position #1181

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pleppik opened this Issue Sep 20, 2018 · 10 comments

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@pleppik
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pleppik commented Sep 20, 2018

Occasionally my MMU2 selector bearing will get confused about its position.

When loading or unloading a filament, the bearing moves to a position which does not engage the correct filament. Sometimes the bearing will engage the wrong filament, causing it to be ejected out the front of the MMU. Other times the bearing will only partially engage or not engage on any filament, causing a load or unload failure.

This happens maybe once every 1000-2000 material changes. When it happens, resetting both the MMU and the MK3 using the reset buttons next to the USB ports will correct the problem. Cycling the power or resetting the MK3 with the front panel button does not reliably fix the issue.

The selector bearing can travel freely to both stops.

@ojrik

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ojrik commented Sep 20, 2018

The screws with the string should be aligned or as shown in the picture without a filament.
pulley body

@pleppik

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pleppik commented Sep 20, 2018

The MMU is properly tensioned. The problem is that the selector bearing is not being positioned properly.

For example, I select "Load Filament 2", and the selector moves to the position to accept filament 2, but the idler body moves to engage a different filament (for example, 4). The result is that filament 4 is ejected out the front of the MMU.

This happens only rarely, but when it happens the only reliable way I've found to clear the problem is to reset the MMU and MK3 using the reset buttons near the USB ports. If I simply cycle the power and allow it to rehome, the MMU will continue mispositioning the idler body.

@B3D-P

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B3D-P commented Sep 23, 2018

Like this? (actually in this case the selector did not move into the correct place) Mine does all kinds of crazy stuff, its driving me nuts. I'm starting to think the drivers or board might be bad.

20180923_090522

@chrissearle

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chrissearle commented Sep 23, 2018

I've had this twice today (first day with the MMU). First time I gave up and powered down.

Second time - I got support involved.

It happened the second time after a filament load/unload issue. This turned out to be a stringing filament under the finda.

The print was a two colour print using 1 and 5. After I cleared the finda - it suddenly gave me a filament load flashing LED on position 5 when trying to load filament 5 - with the selector on position 5 - but with the idler body positioned for filament 1.

We tried a fair number of things - but it insisted on pushing the filament in position one out just like @Blanchard3d pic in comment above.

So - we decided to try one last thing - while the printer was still showing "MMU needs user attention" - I hit the reset of the MMU only.

It reset, selector moved to position 1, and the MK3 suddenly changed back to heating nozzle.

Once the heating was complete - it then pushed the filament out of position 5 with the selector in position 1 and started to beep. But this time the LCD asked me to remove the old filament and then press the knob on the mk3.

I did this - and the unit then did the proper reload of filament 5 (moved the selector to the right place) and the print continued. Still printing now - just hoping it'll complete.

So - I have also seen this, it's definitely that the MMU idler and selector are in disagreement on position - one is one place - the other a different place.

Seems like a definite bug in the MMU firmware.

But - it does seem - as a last resort - that resetting the MMU alone while the printer holds the progress is worth at try - am guessing only as a last resort as I have no idea how reliable this is - but if the print is going to fail anyway - worth a try :)

@AbeFM

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AbeFM commented Sep 30, 2018

This happens to me.

It could be solved, I feel, by just homing the drum more often. Maybe every layer?

Similarly, it can lose track of the output selector, and print with the wrong filament. I have this once in a while, though less since I cleaned up the filament paths. Nonetheless, the wrong sized bondtech gears with a single calibration eventually fill the printer with plastic scrap, and causes any number of jams.

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AbeFM commented Oct 18, 2018

The drum commonly gets lost if it skips, and it skips too easily. Monitoring it is likely a better solution than turning up the current.

@infomagichand

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infomagichand commented Nov 1, 2018

Im gettins the same problem!
every 1 to 3º filament change it get lost

@dikodahan

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dikodahan commented Nov 1, 2018

Saw the same thing. Usually 1-3 moves without an issue, but over to 4 and 5 it sometimes has an issue.
I have to say that if I manually press to move one position at a time, I did not see this issue. However, If I hold the move position to move all the way from 1 to 4 (for example) it gets confused.

@michalxfanta michalxfanta added the MMU2 label Dec 15, 2018

@jlmyra

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jlmyra commented Dec 28, 2018

I have experienced this (pulley barrel getting out of sync with the selector) as well twice in the last 24 hours. I was unable to clear it either time. I have the latest firmware installed- 3.5.1 and 1.0.3. Very frustrating to lose prints after a huge time and filament investment. Support suggested downgrading to the previous firmware release . I think that's the standard solution when they are clueless.

@YoungR0se

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YoungR0se commented Jan 1, 2019

My first multi-colour print (2 colours per layer) was 9 layers in when the drum misalligned. Has been unable to align properly for filament change since then. Tried power cycling, resetting, re-flashing. Nothing makes it work any better :(

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