This is a remix of Michael Fanta's original Gravity Spoolholder for MMU2S, which rolls the spool up a ramp while filament is being dispensed and takes up the slack when the filament is retracted by letting it roll back down the ramp. This works amazingly well except for a fairly loud “clunk” noise each time the gear teeth slip at the top of the ramp.

There are already several remixes of this spoolholder that aim to get rid of the clunking sound. I tried many of them and they either weren't quiet enough or they had a tendency to get “stuck” at the top of the ramp and not rewind. I tried several modifications of these, but could never get them to be 100% reliable.

The Smooth Gravity Spoolholder (by @StayAtHomeBob) is a near-perfect solution for this problem, being both silent and reliable. I prefer the open hexagonal mesh of the original frame sides, and I had some problems with printing some of the parts that had deep notches in them (the wheel hub, in particular) without supports. So, I modified Michael Fanta's original design, drawing heavy inspiration from @StayAtHomeBob's design.

This design uses rubber Lego tires to get enough grip to roll up the ramp. I tried making textured ramp/wheel alternatives out of normal PLA/PETG and even flexible materials like TPU, but they wouldn't reliably roll up the ramp without slipping or they re-introduced some noise. The Lego tire material is perfect for this application. This model is designed to match Lego part #58090, which can be ordered from BrickLink for only a few cents each.

This model is designed to fit the original filament spoolholder bases that come with the MMU2S/MMU3. If desired, a replacement base may be printed from the included model. I found the hexagonal nut that clamps the spool onto the axle to be too small for the hub of any of my filaments, so I would recommend instead using the 42-68mm nut by @ryan3d (not included in this model to give the original designer credit). I would also recommend using the PC4-M10 Clip for Gravity Spoolholder by @volker_puttma_101952 in place of this filament guide to keep the PTFE tube from slipping (also not included in this model). This goes well with the Prusa MMU2 PTFE Holder M10 Passthrough Adapter modification by @vertigo235_33 that also uses PC4-M10 fittings.

Here is a quick video featuring this filament spoolholder (with the above modifications added) so you can see how it works:

Print Instructions

What to print:

1 left frame
1 right frame
1 threaded axle
2 threaded wheel hubs
2 spool nuts
1 filament guide
1 base (Optional, if not using the ones that came with the MMU2S/MMU3)

What to acquire:

2 Lego tires (#58090)

Any print material is fine. I used PLA. For most parts, there are no special instructions for print settings. I used a 0.4mm nozzle and printed at 0.2mm layer height with mostly-default PrusaSlicer settings. No supports are needed anywhere, and I did not need a brim for the axle or wheel hubs.

I doubled the number of perimeters from 2 to 4 for the wheel hubs since you need to tighten them down pretty hard to keep them from unscrewing, and the print layers may try to shear off or separate. Perhaps a drop of glue or a piece of tape on the threads would help to keep them from slipping. For the frame sides, I found that a manual color change at a height of 4.2mm (layer 21) is easy in PrusaSlicer and looks very good.