MMU2s Filament Loading Issue  

Re: MMU2s Filament Loading Issue

Can you provide some more details on exactly what you observe? Do you hear the MMU2S grinding the filament when it's feeding? How far down the tube does it make it? Does it consistently stop feeding at the same point?

Some things that come to mind:

1. Did you upgrade the MMU2 firmware to the MMU2S firmware? This is the first thing that comes to mind because (I believe) the MMU2S just feeds filament until the IR sensor sees it. Where as on the MMU2, it relied on exact tube length calibration.
2. Have you pulled the orange tube off and confirmed there is no debris blocking the pathway?
3. On your MMU2S, do the idler bearings spin freely?
4. Have you tried feeding filament by hand down the orange tube to see if there is any resistance?

Re: MMU2s Filament Loading Issue

Can you provide some more details on exactly what you observe? Do you hear the MMU2S grinding the filament when it's feeding? How far down the tube does it make it? Does it consistently stop feeding at the same point?

Some things that come to mind:

1. Did you upgrade the MMU2 firmware to the MMU2S firmware? This is the first thing that comes to mind because (I believe) the MMU2S just feeds filament until the IR sensor sees it. Where as on the MMU2, it relied on exact tube length calibration.
2. Have you pulled the orange tube off and confirmed there is no debris blocking the pathway?
3. On your MMU2S, do the idler bearings spin freely?
4. Have you tried feeding filament by hand down the orange tube to see if there is any resistance?

Thanks for the response.
1. Yes, upgraded the firmware to the MMU2s version (I think 3.6.0) and I upgraded the printer firmware to the MK3s version 3.6.0
2. Checked for debris multiple times.
3. Yes, checked them when I opened it to make sure the gears were aligned correctly.
4. I have not, but I was able to print with a single filament with no errors.

As near as I can tell there has to be more to the firmware change than just telling the mmu2 to feed until the sensor trips on the extruder. I spent half an hour one night turning the idler tension screws a half turn at a time and attempting to load test all 5 filaments via the buttons. After half an hour I was only able to load all 5 once this way and the idler screws could not be turned more than a quarter turn in either direction without causing it to fail.

Re: MMU2s Filament Loading Issue

I've heard others say that their tension screws were extremely particular as well. I personally haven't found that to be the case. I usually aim for having the bolts line up just below the surface. But even if I go tighter or looser, it generally seems to make very little difference for me. And I even have extra drag on my filament because of my custom mounting for my spools. It runs through several segments of short PTFE tube before even getting to my MMU2.

I'm really not sure what else to try. It seems like it could only be a couple of things. Either the the filament doesn't have a low friction path. Or the MMU2 isn't getting a good grip on the filament. I'm sure stating the obvious isn't much help or consolation to you, but it's got to be something that simple, right? What else could it possibly be?

Re: MMU2s Filament Loading Issue

I've heard others say that their tension screws were extremely particular as well. I personally haven't found that to be the case. I usually aim for having the bolts line up just below the surface. But even if I go tighter or looser, it generally seems to make very little difference for me. And I even have extra drag on my filament because of my custom mounting for my spools. It runs through several segments of short PTFE tube before even getting to my MMU2.

I'm really not sure what else to try. It seems like it could only be a couple of things. Either the the filament doesn't have a low friction path. Or the MMU2 isn't getting a good grip on the filament. I'm sure stating the obvious isn't much help or consolation to you, but it's got to be something that simple, right? What else could it possibly be?

What's annoying is that prior to flashing the upgrade firmware, mine weren't. It would only a couple of minutes to get the filaments loaded. It's even all filament that I've run through before prior to the upgrade. Since the start of the year I've been using the MMU2 as just a quick load system and usually have 4 or 5 different filaments loaded depending on what my next planned print is.

I guess I'll have to take and read the two different firmware's codes side by side and see if I can figure out all the changes.

I'll also maybe do a run of the 3.7.0 firmware that's up on github right now.

Re: MMU2s Filament Loading Issue

The latest firmware for MMU2S is 1.0.5. Have you done a memory reset after the upgrade? If not, try that.

Re: MMU2s Filament Loading Issue

The latest firmware for MMU2S is 1.0.5. Have you done a memory reset after the upgrade? If not, try that.

I miss-typed and left the 1.0.5 part out. That's the one that I used.

Re: MMU2s Filament Loading Issue

I upped to the 3.7.0 RC on github. It did better with 2 filaments. Gonna do some more tests this weekend.

Re: MMU2s Filament Loading Issue

Several days and tests later there is nothing good to report. The update to the Prusa firmware with 3.7.0 helped at least make it so I can print one color. Multi color is just not happening with whatever the mmu2s firmware did to the mmu2.

MMU2s Filament Loading Issue

I have the same exact issue filaments not loading from MMU2S I have MK3S 3.7.0 and MMU2S 1.0.5 firmware any help will be appreciated

Re: MMU2s Filament Loading Issue

I just did the "S" and I found I had the tighten the extruder screw about all the way tight. seems crazy but so far so good. extruder motor is getting hot, but I have a fan I can pop on and that seems to help.

RE: MMU2s Filament Loading Issue

I am having difficulty as well. I made a post here Struggling with FINDA and filament loading on my MMU2S upgrade   which details what I am seeing. The short of it is when I try to load filament to the extruder it pulls a little filament and then ejects it and then acts like there is filament at the extruder and asks if anything is coming out. After saying no a few times to gives up and forces me to select yes. Then if I go to the sensor info page it indicates the FINDA sensor is always seeing filament even when there is none. The LED on the FINDA is working. And before you say it's a bad FINDA sensor, the status page indicates proper operation of the FINDA sensor before I attempt to load the filament. 

I think it's a firmware bug, but I don't see how there could be one so glaring. Please let me know if you managed to resolve your issue.

Thanks,

-Pete

RE: MMU2s Filament Loading Issue

Hi,

I've also had big filament load issues since the Mk3s/MMU2s upgrade and spent much time on it.

My biggest issue was the MMU unit sometimes not disengaging even after the IR sensor triggered during loading procedure.

At the end, I solved it by doing both MMU2 and printer factory reset. I just ran the calibration wizard as it popped up after the reset, nothing more.

Of course, the IR calibration has to be OK.

Also, you should pay attention that the MMU2 selector properly aligns itself to the filament positions. You can remove the PTFE coupler and insert an 1.5mm allen key to check it.

On my last print I had to manually turn the MMU2 selector lead screw of 4 steps to realign the selector. Before that, I was having random load issues.

Hope it can help some of you.

Guillaume

RE: MMU2s Filament Loading Issue

Hi,

The same loading issue came back after approx 3h30 and 130 tool changes.

I think I will now wait for Prusa to find the root cause of it cause I don't have any other idea.

RE: MMU2s Filament Loading Issue

Add my name to the list. Mostly the same problems but I have noticed:

1: It takes 2 attempts for the filament to load most times.

2: Most fails on the second try have some of the previous filament on the end.

3: There are some fails where the extruder stops turning and then the mmu tries to unload the filament. All this does is grind down the filament   under the bearing because the filament is trapped in the extruder.

4: There are some times when there is a grinding noise that sounds like it is coming from the extruder. Print fails at this time.

5: The nozzle oozes a large blob when it gets stuck and I have to cut it off the wipe block.

I have all the latest firmware and all gears are lined up.

The filament is a bit hard to pull through the whole system, but not overly so. I have ordered larger id tubes to replace the old ones.

It would be great to know if Prusa is doing anything about this. This is such a great idea but I just can't get it to work.

RE: MMU2s Filament Loading Issue

Verify that the IR sensor is functioning properly by navigating to the Support, Sensor Info screen while something is printing.  It should display a constant value of 1, not alternate between 0 and 1. 

Several of us had an issue where the static IR filament sensor calibration looked just fine but the sensor didn't reliably detect filament during actual operation because the extruder idler door "flag" doesn't extend far enough into the chimney.  The vibration from loading/unloading/printing is enough to produce intermittent indications, causing unreliable loading and unloading.

The solution is to print a door with a larger flag that can be filed down to exactly the right size.  See https://www.thingiverse.com/thing:3572252.   You can also use a bit of masking tape to enlarge the flag.

RE: MMU2s Filament Loading Issue

Thanks for that @jim-l5. I may give that a shot before taking apart the whole extruder to convert to the Butterwork indirect filament sensor (MK3) variant.

RE: MMU2s Filament Loading Issue

@jim-l5 thanks indeed for that door update. I ran it off this evening and after some sanding I was able to make my first successful (non mmu) print with the IR sensor enabled. 

The door in general also seems to fit better as I can now manually feed filament past the gears like I used to be able to do before I upgraded to the 3S. So double thanks!

RE: MMU2s Filament Loading Issue

After much trial and error with settings, chimney adjusting, tension adjusting and crying, I decided I would give it a try by just feeding filament through a 6 inch tube directly in to the mmu. Well imagine my surprise when it worked perfectly! 

Even though with the buffer on it didn't seem like much effort to pull the filament through, it was hard enough to make it fail. 

I now have the spools above the printer with the filament routed through 5 pulleys  mounted on the wall behind the printer at mmu level. It looks like a spaghetti junction, but it works without fail and doesn't get tangled.

RE: MMU2s Filament Loading Issue

Posted by: robert.f16

After much trial and error with settings, chimney adjusting, tension adjusting and crying, I decided I would give it a try by just feeding filament through a 6 inch tube directly in to the mmu. Well imagine my surprise when it worked perfectly! 

Even though with the buffer on it didn't seem like much effort to pull the filament through, it was hard enough to make it fail. 

I now have the spools above the printer with the filament routed through 5 pulleys  mounted on the wall behind the printer at mmu level. It looks like a spaghetti junction, but it works without fail and doesn't get tangled.

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Agree with you about the MMU being very sensitive to friction.  This was one of multiple issues I needed to resolve to eliminate frequent load/unload and missed layer issues.  I have a very compact setup, with the spools below the printer.  What worked very well for me was to upgrade the input side of the filament buffer to 6mm PTFE tubing and leave the output side of the MMU with the stock 4mm tube. 

You don't want too little resistance either or the filament sometimes unloads too much.