mmu2s mk3s ir-sensors, differences between the two types?
 

mmu2s mk3s ir-sensors, differences between the two types?  

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John Svensk
(@john-svensk)
Eminent Member

I have taken up an old project - building an extruder for the "Mk3s/MMU2s" with a Flexion HT sitting on top of the default V6 hotend and heat sink. Then a thought struck me: what is the difference between the Mk3s IR sensor and the MMU2s (with the longer lever)?

-- Will it matter which sensor variant I choose?

And: is the printer firmware sensitive to changes in distances, e.g. from the FINDA in the MMU2s to the IR sensor and then to the nozzle?

Best Answer by Dave Avery:

the MMU2 needs a sensor that detects the filament being captured by the extruder bondtech gears. thats why the door and chimney. or the various schemes that the bear/bondtech/BNBSX extruders use to replace the chimney. the key is the MMU needs some machanical sensing that is tied to the position of the bondtech idler door position

Posted : 13/10/2019 9:02 am
ACE
 ACE
(@ace-2)
Trusted Member

On mine there was none. I think they packed the IR sensor with the MMU2S kit for those users with an older model upgrading to an MMU2S. So if yours is the same there won't be a difference.

Yes you will need to adjust for those changes in length. The distance between MMU2s and extruder can be adapted without changes to the firmware by calibrating MMU2S tube length for each filament (1 to 5) via the MMU2s service mode. I think the procedure is in the manual.

The distance between nozzle and extruder gears needs to be adapted in firmware.

This post was modified 2 years ago by ACE
Posted : 13/10/2019 1:48 pm
John Svensk
(@john-svensk)
Eminent Member
 
 
Posted by: @christoph-e5

On mine there was none. I think they packed the IR sensor with the MMU2S kit for those users with an older model upgrading to an MMU2S. So if yours is the same there won't be a difference.

That's a bit weird, because the IR sensor is the same in the two kits. The difference is in the mechanical construction that breaks the light beam... The Mk3S has a short (20mm/0.8in?) lever, but the MMU2S type is 2-3 times longer and I guess more sensitive? It is highly probable that I'm exaggerating the differences, I just want to understand and make an educated guess as to which type will be best for my build... Right now I'm leaning towards the simpler Mk3S sensor build. 

Mk3 to Mk3S kit:

MMU2S:

Thanks for the input, yes the "bowden tube" calibration is available among the FAQ:s, I think.

This post was modified 2 years ago 2 times by John Svensk
Posted : 14/10/2019 7:43 am
Sembazuru
(@sembazuru)
Prominent Member

The differences you are seeing is where (and how) the sensor is tripped between the MK3S and MK3S+MMU2.

With the MK3S there is a ball bearing in the filament feed path. This ball bearing moves the arm to break the beam. Here the filament is sensed slightly before it is engaged with the bondtech gears. Not a problem when hand-feeding the filament, but it would signal the MMU2 to stop feeding the filament before it is engaged with the bondtech gears.

With the MK3S+MMU2 the arm to break the beam is part of the bondtech idler door. With this one, the filament needs to actually push the bondtech gears apart to break the beam. Here the filament is sensed when it is engaged with the bondtech gears.

I don't know why they didn't keep the MK3S design for the MK3S+MMU2 and have the MMU2 stop feeding the filament a known distance between the trigger point and the bondtech gears. Maybe because that distance could be slightly different between builds? That is just a guess though.

See my (limited) designs on:
PrusaPrinters - https://www.prusaprinters.org/social/1448-sembazuru/prints
Thingiverse - https://www.thingiverse.com/Sembazuru/designs...
Posted : 14/10/2019 7:56 am
ACE
 ACE
(@ace-2)
Trusted Member

sorry johnsvensk, I misunderstood your question and thought you were literally refering to the sensor - not the triggering mechanics.

I do feel the mmu2 chimney is really a bad design choice - not only looks but also serviceability. I cannot comment on using the mk3s style sensor mechanics with an mmu2 - never tried that. I‘ve switched to a different extruder and have no need for the chimney thingie for reliable filament sensing.

Posted : 14/10/2019 8:05 pm
John Svensk
(@john-svensk)
Eminent Member
Posted by: @christoph-e5

sorry johnsvensk, I misunderstood your question and thought you were literally refering to the sensor - not the triggering mechanics.

Understandable, I had problems finding the correct words... The joys of having English as your second language! 😋 

I do feel the mmu2 chimney is really a bad design choice - not only looks but also serviceability. I cannot comment on using the mk3s style sensor mechanics with an mmu2 - never tried that. I‘ve switched to a different extruder and have no need for the chimney thingie for reliable filament sensing.

Yeah, that chimney is really not my favourite... Too sensitive.

A compact version of the Mk3S sensor

Posted : 16/10/2019 6:57 am
Dave Avery
(@dave-avery)
Honorable Member

the MMU2 needs a sensor that detects the filament being captured by the extruder bondtech gears. thats why the door and chimney. or the various schemes that the bear/bondtech/BNBSX extruders use to replace the chimney. the key is the MMU needs some machanical sensing that is tied to the position of the bondtech idler door position

Posted : 16/10/2019 4:32 pm
ben_r_
(@ben_r_)
Trusted Member

Yea I was a bit surprised by how many redundant parts came with the MMU2S kit that I already had from my i3 MK3S build. The IR sensor was probably the biggest surprise. Now Im waiting for the support documents to show up for the new Original Prusa Mini to find out if it uses the same IR sensor. If it does thatll save the $20 they are charging to add it to a Original Prusa Mini order. Eh, if something right? And of course that is IF I decide to order a Mini. I think Id rather wait for the MK4 upgrade kit and put the money towards that though. Gotta see how much the XL printer is going to cost too! Soo many decisions!

If at first you don't succeed, redefine success!...
Posted : 16/10/2019 7:25 pm
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