Struggling with FINDA and filament loading on my MMU2S upgrade  

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

Have you done the IR sensor calibration? You need to make sure the IR sensor is working properly on top of the extruder or it'll get stuck in a loading/unloading loop until it gives up (2 or 3 tries, I think).

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

Both the FINDA sensor and the IR sensor need to work robustly and give the correct sensor readings everytime.

It sounds like you attempted the FINDA calibration. You need to get the probe height just right. If it's too low it can easily read '1' all the time and you might sometimes feel lots of resistance when you push the filament in to test it (using the sensor reading as you said). Conversely if it's too high you might get '0' all the time. Test it over and over again to make sure it's robust and friction-less. As I understand it the green LED means the filament is 'loaded' (i.e in the right position in the MMU2S gears and tube - not that the FINDA has detected it).

The IR sensor calibration is detailed in section 7.1 of the MMU2S user manual. As it says inserting the 1.5mm Allen key into the filament path must give clear 1 (in) and 0 (out) readings every time. It it's right only 90% of the time you'll have problem on 10% of your loads. So again test over and over.

I'm not sure about your nozzle crashes.

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

Hi peter-j16,

I had this issue when I reinstalled my MMU2 unit after I had disconnected it for some single material prints.

In my case, doing the individual filament calibration for filament 1 solved the problem.

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

I have calibrated the FINDA sensor and the IR sensor. I think this might be related to the IR sensor though. What I don't understand though is that the FINDA sensor is clearly reading no filament present yet the printer is thinking that material should be coming out the extruder. The only way that could be is if there is a firmware bug. The main CPU is thinking the FINDA sensor sees filament but it does not. It is not asking the MMU processor and just believes there is filament there. It should not be doing this since it was the one that backed out the filament.

I will try to do an individual filament calibration. 

Thanks

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

I also noticed that the FINDA status in the support menu is either very late or not updated at all, so I don't rely on it. Better check its led.

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

I upgraded to the latest firmware and did the filament calibration all with no luck. 

There must be something simple that is wrong. Unfortunately, it is clear that the firmware is very dumb and only looks at sensor values at particular moments in time. The FINDA sensor is checked when loading the filament but then is assumed to indicate filament from then on. Even if some other part of the firmware decides to back the filament all the way out. This is obviously a side effect of having such a basic microcontroller for all of this. No way to support more complex code or multi-threading. 

I would love to get the MMU2S working, but at this point I would settle for just a printer that works.

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

The first is that I can't get the printer to load any filament. If I run the first layer calibration, it just starts the run without loading filament. Also when this runs the adjustment for the Z axis seems to have no effect. It just jams the nozzle into the print bed (ruining one side) and never lets me raise the Z axis. The know reads a new value, but the nozzle does not seem to raise and continually drags across the print bed.

Every time you do such a large change it is recommended to re-calibrate basicly everything. I allways start by manually calibrating Z, then mesh-bedleveling. If you here remove the steel-plate, use a paper, and you're on guard; the plate should not get damaged.

The other issue is that the printer does not load any filament for this procedure. It is even worse than that. If I try to load filament to the nozzle, it actually unloads the filament. Then asks me which filament I want to load. I tell it, and then it immediately asks if there is filament coming out of the nozzle. But it hasn't even loaded any filament through the MMU2S.

Had the same issue. In the handbook it says how to calibrate the filament sensor, but from what i read you have alreaddy solved this

[...] Unfortunately, it is clear that the firmware is very dumb and only looks at sensor values at particular moments in time. The FINDA sensor is checked when loading the filament but then is assumed to indicate filament from then on. Even if some other part of the firmware decides to back the filament all the way out. This is obviously a side effect of having such a basic microcontroller for all of this. No way to support more complex code or multi-threading. 

The finda does "continuously" read the value, which is needed to detect filament runout during printing. If this is not in place the printer would require humen intervention even if in "spooljoin" mode as the extruder would not notice utill it is too late. 

The 8-bit board is still about as complex(but faster) as what got us to the moon. Now given how insanely fast things actually happen, one would think concurrency is not needed, but the ATmega2560 processor is acutally capable of running multiple threads.

So finally:

Calibrate all sensors, and make sure you have not damaged the F.I.N.D.A. sensor. And if the nozzle crashes into the bed, then 1. there should be a paper there during test, and 2. try changing the P.I.N.D.A. height, as it might be too high

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

So implemented the LED on the filament IR sensor. I highly recommend doing this. It is very helpful to know if the filament sensor is actually seeing the filament. 

I think I may have found the problem thanks to the post here https://forum.prusa3d.com/forum/original-prusa-i3-mmu2s-mmu2-assembly-and-first-prints-troubleshooting/i-am-at-a-complete-loss-mmu2s-fails-to-even-fail-consistently/.

Increasing the extruder idler tension a lot seemed to fix things. The LED let me know the could load to the extruder even with the tighter idler tension. I think that Prusa really needs to look at the firmware and how it responds to this issue. 

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

Posted by: karl.w2

Have you done the IR sensor calibration? You need to make sure the IR sensor is working properly on top of the extruder or it'll get stuck in a loading/unloading loop until it gives up (2 or 3 tries, I think).

Interesting... I have this exact problem, but the IR sensor calibration is ok!
I have spent six hours on this problem with Prusa Support, and I haven't come a millimeter closer to a solution...

I hope to publish a condensed version of my chat transcripts in this forum today, hoping that one of you big-brained people will find what Support didn't. 😊 

RE: Struggling with FINDA and filament loading on my MMU2S upgrade

Hi everyone,

I had similar problems. After a few days of trying fixing testing...and failing in many different ways I found out that the cable of the FINDA probe did not have proper connection.

When I tested the probe it usually worked but after a while of printing caused different filament retractions, blockings a.s.f.

Finally the FINDA value was stuck on '1' even when completely removed. Only when I wiggled and kinked the cable with a bit of force it would eventually work again.

I now had to bend the cable at a 90 degree angle and fix it with a cable binder to the sensor as a workaround. This is Abit of a drag when the selector moves to the right end.

So eventually I'll ha e to order a new FINDA probe I guess.