How to change how the MMU2S reacts to the sensor near the idler at the printhead
 
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How to change how the MMU2S reacts to the sensor near the idler at the printhead  

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David R
(@david-r)
Active Member
How to change how the MMU2S reacts to the sensor near the idler at the printhead

Hi All, here is what I need:

Problem: I have the MMU2S and MK3S. The filaments make it to the sensor at the direct drive, but then the idler never grabs them. I have run all the checks and all the tutorials. I have figured out that the issue is that the MMU2S stops pushing the filament the instant the filament touches the Sensor by the idler at the print head. it should push about 1/4 to 1/2 inch more past that point. That way the idler can grab the filament and begin printing.  Manually, I have removed the feeder tube allowed the MMU2S to feed about 1/2 inch more of material then sent it down to the idler and it prints flawlessly. so I need a way to get the MMU2S to push just a bit more material past the moment the sensor at the printhead idler switches to 1 form 0. 

Possible solution: increase the amount of filament the MMU2S pushes after the sensor tells it that it reached the print head.

How? : No idea. Maybe custom snippet added to the machine via the prusa slicer? maybe right after the gcode tells it to wait for the sensor input, i could add a feed gcode for a few additional mm of material? but it would have to be included on every material change as well.  There has got to be a better way.

Best Answer by Baklin:

The MK3s has the right sensor, but it has to be moved to the chimney that you need to install (and remove the steel ball and the parts that holds the ball)

The extruder has to look like the picture you posted and with the filament sensor at the top of the chimney.

 

No need to disconnect all the connectors, but you need to pull the sensor cable out a bit more to reach the chimney. I didn't need to loosen all the screws at the back of mine to pull out the cable. But maybe you will if the cables can be a bit tight.

https://help.prusa3d.com/en/guide/2b-mk3s-mk2-5s-extruder-disassembly_38120

 

After that you need to up grade the extruder like shown here: https://help.prusa3d.com/en/guide/3b-mk3s-mk2-5s-extruder-upgrade_41560

 

Better read the full instructions to make sure you understand it all and do all the steps needed.

Also have a look at the handbook when you are done. It has a lot of useful info.

https://cdn.prusa3d.com/downloads/manual/prusa3d_manual_mmu2s_en.pdf

 

I'm going to spam this video here again. This has helped me a lot in understanding how the MMU works.

Posted : 28/07/2021 4:19 pm
Nikolai
(@nikolai)
Noble Member
Fix the root cause

My guess would be wrong firmware on MMU or MK3. Double check you have the correct one flashed. There are different versions for different type of sensors. The combination MK3/MMU firmware should also match. If you're building from scratch, I would recommend to download the most recent one (for your printer version)

Often linked posts:
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Posted : 29/07/2021 8:31 am
David R
(@david-r)
Active Member
Topic starter answered:
More info

For the MMU2S the firmware is 1.0.6-372 and for the MK3S its 3.10.0-4481 As far as I can tell its the latest firmware. The MK3S was built at the factory, the MMU2S I built from the kit. I dont think its behaving wrong. I think its responding to quickly. like I stated, the filament makes it to the sensor at the hot end, but it stops the second it interacts with the sensor. It still needs about 1/4 to 1/2 more of travel to reach the idler gear. In the image attached the first side shows how much filament is pushed and how it stops as soon as it hits the sensor. the second picture is how much it actually needs to reach the idler gear.

 

Posted : 29/07/2021 11:13 am
Baklin
(@baklin)
Reputable Member
title

The filament sensor on the extruder for the MMU is triggered by the filament that gets between the bondtech gears. If the sensor is triggered the filament should be between the gears and the extruder should be able to grab it.

 

Do you use the modified extruder for the MMU. The MK3s and MK3s/MMU use different extruders with the filament sensor placed in a different location.

 

https://help.prusa3d.com/en/guide/3a-mk3s-extruder-upgrade_188808

 

Just want to make sure as the triggers points between the 2 extruder versions is about a 1/2 inch.

Posted : 29/07/2021 5:43 pm
David R
(@david-r)
Active Member
Topic starter answered:
Followup

The manual, if I understood it correctly, said that for the MK3S the sensor was already in place. Am i supposed to put the new chimney ? If you look at the pictures I posted above, the top of my print head does not look like the one i posted with this reply. Did i misunderstand the manual? Did I miss some build portions?

Posted : 29/07/2021 6:24 pm
Baklin
(@baklin)
Reputable Member
title

The MK3s has the right sensor, but it has to be moved to the chimney that you need to install (and remove the steel ball and the parts that holds the ball)

The extruder has to look like the picture you posted and with the filament sensor at the top of the chimney.

 

No need to disconnect all the connectors, but you need to pull the sensor cable out a bit more to reach the chimney. I didn't need to loosen all the screws at the back of mine to pull out the cable. But maybe you will if the cables can be a bit tight.

https://help.prusa3d.com/en/guide/2b-mk3s-mk2-5s-extruder-disassembly_38120

 

After that you need to up grade the extruder like shown here: https://help.prusa3d.com/en/guide/3b-mk3s-mk2-5s-extruder-upgrade_41560

 

Better read the full instructions to make sure you understand it all and do all the steps needed.

Also have a look at the handbook when you are done. It has a lot of useful info.

https://cdn.prusa3d.com/downloads/manual/prusa3d_manual_mmu2s_en.pdf

 

I'm going to spam this video here again. This has helped me a lot in understanding how the MMU works.

Posted : 29/07/2021 6:43 pm
David R
(@david-r)
Active Member
Topic starter answered:
Balkin does it again

This was the fix. Thank you so much. The manual was a bit confusing so I missed the change on the chimney and the change of the sensor. I just completed the changes and did a "Load to Nozzle" and it worked beautifully 🙂 Thank you once again. Now I don't Have to sit there watching the filament load and change 

Posted : 30/07/2021 2:04 pm
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