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Prusa MMU2S Door Sensor for Bear Extruder and MK3S Sensor

by vertigo235 Mar 6, 2019
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Will this IR sensor modification work with the stock Prusa i3 MK3s? I would like to replace the one that came sock and I do not have a bear extruder but would like to know If this would work with my stock Prusa. If not, what parts would I need to print along with IR sensor to make this work?

Any chance you would make a mosquito version of this?

The plug and wedge should work with this mosquito remix, https://www.thingiverse.com/thing:3733768

Prusa MK3s Bear X-Axis Mosquito Hotend Extruder (PINDA + BLTouch)

Hello vertigo235,

for the passthrough body i need a longer PTFE tube, right?

Yes that is advisable, I recommend 3mm ID PTFE.

Yes that is advisable, I recommend 3mm ID PTFE.

Ok, thanx for the Info.

I just tried with a little spare PTFE Tube. Looks like i need to set the Tube length via service menu. Can this be? I tougth with the new IR sensor the filament calibration is obsolete. :)


Yes you still use that to calibrate the distance if you have a tube that is longer, it allows the MMMU2S to feed the filament faster to the gears.


Do your recomend the PTFE with ID 3 only for the Bowden or also for the Tubes to the Spool Holders?

The tubes to the Spool Holders are too short for my setup so i need to buy some.

btw. Great Mod... your solution for the door sensor works out of the box. Had some testing with a door sensor for BMG and the prusa stock, they are a pain. Yours is the best! :) On my other bear i am using your LA1.5 FW... thanx for your great work vertigo235! :)

Thanks! I use regular 2mm id from spools to the mmu

Sorry to ask again a question, but where do I have to attach the 'plug' and 'plug wedge' to?


If you use the passthrough body you do not need the plug and the wedge. They are designed to plug the mk3s filament see sensor cavity, where the lever and ball bearing would go.

is your design also compatible to the MK2.5s mmu2s bear?

It should be yes, but the passthrough body is only compatible with the MK3S, I guess I need to make an mk2.5S passthrough option, thanks for reminding me.

It would be nice, if you would make the option.

But are you sure it is only compatible to mk3s? At github the passthrough/extruder_body is in the section of "common to all versions". Just from comparing these two in slicer they are completely identical besides the modification from you.

Hmm I think you might be right. Maybe it's the mk2 that needs a different body. For some reason I thought the pinda position was different.

I'm rebuilding bear + this mod for mk2.5s, and so far I didn't encounter issues. But I didn't put extruder together yet.

Any news? I'd love to do the Bear extruder and x axis mod on my MK2.5S MMU2S, but I want to make sure that this all works together nicely before diving in.

Sorry yes, I was mistaken the passthrough is compatible with the MK2.5S

Excellent! Thank you for the quick response!

Hi vertigo235. Now were you using a particular firmware mod with your design, of can stock be used. Weighing options for the reliability aspect. Thank you, it is a great design.

You can use stock FW

Can someone explain where the ball bearing plug is supposed to be installed? Thank you!

In your spare parts bin, you don't use it with this mod. There is a 3d printed plug and block to close up the hole and provide a closed path for the filament.

Great work! Can't wait to try it. Is there a filament sensor cover that will work with the festo that comes with the mmu? All these seem to be m10 size.

No plans to support this, the pass through is important to getting the PTFE as close to the gears as possible for best reliability.

Which brass insert or adaptor is needed to use with the cover?

no brass insert, the threads are 3d printed. You use a PC4-M10 coupler

Just wanted to clarify. Can I use this on my current MK3 and MMU2s that I am currently going to put together? I have the current Bear extruder from GitHub.


Yes that is the version I'm using, I will note that I installed a JST connector to give extra clearance of the top frame however.

I am working on my first Bear and ran across this. Wasn't aware of another extruder mix as well its very interesting. Is there a benefit to using this vs the MMU2s upgrade kits version? I see the arrangement is different and the pass through its a nice touch. Does it save space anywhere, guarantee a detection better, or other benefits? Just want to wrap my head around the goal. Thanks for your design and work its very polished.

I created this so I could use my bear extruder with the MMU2S door sensor, I consider the bear extruder to be superior to the MK3S extruder, and I already had it installed on my printer. I plan to redesign this mod once Greg finalizes his MK3S bear extruder updates as well.

Comments deleted.

Is this meant for the v0.6 Bear Extruder or the dev version?

For the .6 bear version at the moment until Greg finalizes his new MK3S design. After that I do plan to redesign this.

Hi, is your update from 6/7/2019 now compatible to the previous dev bear (latest from master on github) extruder?

I like this design even more then prusa's one!

Were you ever able to confirm whether the Molex connector will work with this?

Someone has tried and says that it will work but it's going to be super close. I might do a redesign but it's not a priority at the moment since it's working for me with the JST connector.

I'll try to get a photo with the molex attached to it later, have a long print going at the moment.