NEW – v2: Better planetary gear (more planets, deeper teeth) and better shape (so the rope doesn't jump off the pulley). Also using my own planetary gear code now.
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A quite strong pulley / snatch block utilizing a planetary gear as bearing for lower friction. The snatch block/swing cheek pulley can open up to be attached mid-line, i.e. without pulling all the rope though. It is based on my pulley system (block and tackle).
WARNING: NOT FOR CLIMBING! The strength of this model is not tested and depends on a lot of factors. Do not use in any circumstances where failure endangers life or health or valuable objects.
Printing: Use more walls/perimeters, e.g. 5. I actually printed mine with 100% infill.
I used a 0.4mm nozzle and 0.2mm layer height, but that's probably not critical. I also used PLA, but stronger filament would be, well, stronger.
The tolerance is quite tight; for my printer (Prusa Mini) and filament (recyled PLA) the bolts need some forceful persuasion to go in for the first time, but it gets better (and quite perfect for me) after some breaking in. The same applies for the planetary gear bearing: it might be difficult to free up (I mounted it in the snatch block to get grip on the sun gear), but after quite some breaking in it runs quite nicely without much play.
Since printers and filament vary, I also added parts (bolts and bearing) with more tolerance.
The author remixed this model.
Better planetary gear (more planets, deeper teeth,
better shape (so the rope doesn't jump off the pulley)