Skelestruder for Prusa MMU2s and reverse Bowden

thingiverse

I moved specific parts for MMU2 and reverse Bowden support to here. See main source at Skelestruder on Thingiverse for details. Also check out Hairlock for MMU2 information. Pcover is designed for standard filament sensors and requires one brass heat set nut from Amazon. PM6cover is similar but has threads for PC4-M6 couplers. PI-lid is used with indirect filament sensors and needs a single brass heat set nut. PIM6-lid has the same design but includes threads for PC4-M6 couplers. Frame bracket helps clear wiring and I tilted it up more, which is helpful when using hanging spools. Recommended print settings are PETG at 0.2 layer with 20% gyroid infill. --- I updated parts so they can be printed correctly now. Fixed the idler's scaling issue and added a bit of thickness to the arm. Here's a beta release of MMU2S IR sensor support. My first test of it produced a complete, flawless multi-color print without assistance. This looks promising. I wanted to test more but some users are eager to try it out and I'm on vacation right now, so be aware that this is not final quality yet. I created this as a mostly bolt-on for testing purposes and it's quite hacky at this stage. I plan to revise and integrate it later. Why did I design it this way? When Prusa announced the MMU2, I decided I wanted it to require minimal changes and preserve other essential features. For example, I still want quick access to gears by simply opening the idler door without any tools, which is a hallmark of Skelestruder. This feature becomes even more valuable when printing with MMU. I also wanted to keep it compact while amplifying the mechanical swing to increase error tolerance and require no adjustments. So, I went with dual pivot, but that requires bearings for reliability. However, many users already have them from the indirect sensor solution. A plastic spring? Yes, but its flexibility is almost zero; it merely assists gravity, so I expect it to be reliable. Printing: Recommended settings are PLA or PETG at 0.15 layer height. IR_arm needs supports, and make sure you clean off well after removing. I recommend printing two each of pivot and arm in case you have installation issues. How to assemble (I don't have access to my printer right now, so this is from memory and some photos I found on my phone): See the nice photos by @panayiotis_3d in the comments for a better understanding. You'll need two 673 bearings, same as used in the indirect and hybrid sensor solutions I posted. Press one bearing into the pivot and screw the other into the idler side using an M3x10 screw. Also, you'll need a heat-set M5 nut; install it into the lid. Remove your current sensor cartridge and set aside. Use the M2 screw that came with the IR sensor to screw it into the IR cartridge with the slot toward the rear. Slide the cable connector onto the IR sensor with the spring-catch facing left (see Prusa's installation pictures). Insert the cartridge into Ecage and add the lid. Screw down using M3x12 or 14 in front, then use M3x12 for the rear and attach the cover first with the tab up. Don't tighten it fully so you can slide the cover open. Pull the IR cable up and snake it through the posts on the lid to secure it. Press the arm into the bearing on the pivot and make sure it's fully seated and swings parallel to the plane. Swing over top and insert the end into the cartridge, making sure it slips easily into the IR sensor slot. Swing the cover closed, ensuring the arm spring is underneath the cover. You might need to press it down slightly. Reinstall any removed parts of Skelestruder, plug the IR cable into Einsy following Prusa's instructions, and change your firmware variant to MK3s. Rebuild, flash the printer, go to the support menu/sensors, and make sure IR is zero. Lift the idler slightly and confirm it changes to 1. Run a small test print. Fine-tuning arm for this beta release: if you have to lift the idler more than a fraction of mm to trigger IR, wrap one or two pieces of scotch tape around the arm where the idler roller contacts it. Conversely, if you see triggering while unloaded, shave a tiny sliver off the arm where the roller hits (think thickness of tape). After getting it dialed in, it shouldn't need further adjustment.