UPDATE 13/10/2019: I've released a new E2 version, wich addresses some issues found when unloading filament after runout (see DonKarnage comment on Sep 29, 2019). However this new version has not been tested by me. Please leave a comment if you are using it. Thank you.
This version of the Prusa MK3 MMU 2.0 selector combines three interesting ideas from Thingiverse users:
"MMU2 Filament Selector w/ Mag FINDA Sensor fix 6mm" by TimGold (https://www.thingiverse.com/thing:3264138). Adding a small magnet under the FINDA ball chamber, to help keep the ball down and to prevent it from remaining lifted up when the tip of the filament ends with a string or there are some debris left in the chamber. When the ball stays up, the MMU detects an incorrect filament length, thus causing problems during loading and unloading.
"Prusa MMU2 selector mod" by jltx (https://www.thingiverse.com/thing:3199061). Partially opening the FINDA canal and chamber, to monitor filament loading, observe the ball status, set the FINDA height visually and extract debris mid-print.
- "PRUSA MMU2 Selector Improvements" by kmccon (https://www.thingiverse.com/thing:3157550). Chamfers and fillets were added in a few places to smoothen filament path.
Moreover, I've made some little modifications:
- Smoother holes and passages (some more fillets and chamfers)
- Simpler insert for the magnet. Instead of inserting it from bottom, I opted to push it from one side, reducing the hole needed.
I'm using a 6x2 mm round neodymium magnet (real thickness is 1,73mm, I bought these: https://www.aliexpress.com/item/6x2mm-round-Neodymium-magnet-N50-N52/32872232504.html), but you can easily change it using Fusion 360 sources included.
You will need a longer M3 bolt to hold the POM nut. The original is 10mm, but you will need at least a 15mm-16mm.
Warning: there are some bridges in the model, so I suggest to configure proper cooling. In Slic3r, I checked the option "Detect bridging perimeters" in the Print Settings tab. As to filaments settings, I decreased extruder temperature to 225 °C (used Prusa PETG) and increased fan speed (min 50%, max 100% and bridge 100%).
Unmounting the selector
To install just follow the directions for changing the blade (see MMU2 Handbook) which requires removal of the selector. Tip: remove first zip tie on finda/selector motor wires. It’s not needed and prevents you from backing out the motor for selector maintenance. As you back it out, rotate body so wires point to back for more slack to clear the selector.