Filament unloading and other issues....like the dangerous blade that catches on the assembly.  

Filament unloading and other issues....like the dangerous blade that catches on the assembly.

So this MMU has been a nightmare....for starters  What happens is...when it goes to unload.  The extruder pushes out the filament...but there remains loose string inside the extruder gears.  ..you konw from it instantly pulling out 220 degree filament...the IR sensor goes off , because the main body of the filament is no longer in the extruder....and the light stringy stuff....isn't thick enough to set the extruder IR sensor off but is still in the gears of the extruder.  And so the MMU continues to try to pull the filament....causing it to grind down the filament in the MMU. And if it manages to pull the filament free....it's not like you've solved a problem...because not that lighty stringy stuff....is now clogging your extruder.  And if it doesn't pull it free.... you still have a clogged extruder....and now a clogged mmu.  I've not got a successful print from this yet.

In the end....all I end up with is extruder clogs and mmu clogs.  Every time.

I couldn't have designed a better machine to clog my machine if I've tried.

And that is not the only issue I've had.  Let's talk about the 'cutter'.  When even when you clean up the channel that it slides back and forth in, which I did with every part of this mmu...made sure all lose strings were cut off...all sides and corners had nothing that could catch...I spent time cleaning this up before I started anything.......it still catches.  And the first time i cut on, and caught.  I didn't realize what was catching.  Only that the filament selecter kept getting stuck.  So I put some umph behind it to make it move.  And the razor...digging into the idler body frame....Stayed right where it was.  While the filament selector and my hand...moved fully to the side of the stepper mottor. 

I'm not even mad about the emergency room visit.  Which I do consider to be caused by the design flaws in this MMU.  (When sharing this story I heard other similar stories and a chorus from everyone to remove the cutter blade as it's only function is to get stuck apparantly.)   But I'll take that as my own personal loss.  I was more careless than I should have been and I know better.  Even after cleaning the channel up further and reinstalling the blade.  It didn't catch for a little while...until it did again.

BUT....the rest of this is a design problem.  All it would take is for the firmware to tell the extruder to continue to rotate the filament out for an extra 2 - 3 seconds when unloading and this wouldn't be happening.

And you're telling me in their rounds and rounds and round of testing....that they've never had this happen?  Even though here are two people a week apart who have this occuring in this forum alone., and I've spoken to others who have experience the same problem in the past.

Prusa.  I love your printers.  I absolutely love your printers.  But the fact that you let these MMU's leave your facility in this design shape....   is upsetting to me.  I've not had one successful print.  It's turned my favorite thing in the world, my prusa mk3s+ into junk.  I've literally had clogs happen on every entrance of each filament section.  Every exit of each filament section, and it clogs my extruder every single time it tries to unload filament.

I'm not a coder/programmer.  But how hard could it be to simply say...on unloading filament....have extruder continue to spin for 3 seconds after IR sensor is no longer engaged in order to clear the extruder of all long stringy material you get from pulling out 220 degree filament.

And that's not getting into the fact that every time you unload filament.....the filament is now in horrible shape.  Which i'm assuming is what the cutter, that doesn't function right, was originally designed for.....becaues now that end of the filament thats in horrible shape....on the few amazing times i've had it leave my extruder without jamming.  Now it just gets jammed in the mmu system the next time it goes to load....because its a mushed up janky end to filament.

What am I supposed to do with this?  And yes...I've played with the IR sensor and moved it every single which way.  I've spent tons of time trying to troubleshoot this...which is why i know exactly what's occuring.  I am very experienced not just in 3d printing...but in building electronics, building in general... I've been a maker for decades and I literally own a construction contracting company.  So...this isn't just some new guy in over his head.  I've built 3d printers from scratch...and no not kit systems...or systems designed by someone else who's instructions i followed...i'm talking about from scratch with just me and my own hand picked ordered parts.

If this was from another company i would just kinda shrug my shoulders...it's expected from some 3d printer companies.

And yeah...I had heard the horror stories before I bought this....but I never would have thought that prusa would have let a device leave their facility with this kind of basic design flaws.

Come on man.  Really...come on man.  

But now I've told you what would fix it.  Add 3 seconds to extruder rotation time on every unload command after IR sensor is no longer tripped.  There would be no negative association for you doing that either.  No bad consequences...if someonmes not having this problem...then their extruder motor just spins an extra 2 times, big deal.

But at the moment, I have a hand I won't be able to use for 3 weeks, which will probably cost me thousands of dollars in income.  I have a worthless MMU....and I can't stand to look at my favorite 3d printer, which is honestly the one hobby I enjoy in a world full of crap.