Design uses geometry and operating principle borrowed from this model:
https://www.thingiverse.com/thing:170320
I transposed its dimensions into new bodies, scaled it, adapted the crank to fit the extruder and modified the crankcase to fit the extruder housing.
Will require glue - I attempted many a crankshaft variant only using magnets but with the weight of the rotor and the minor amount of force required to move it around the teeth inside the crank case, it rarely, if ever, moved appropriately. I attached mine using a 4mm x 1.5mm thick magnet and a drop of super glue and it works marvelously that way. Files are provided with and without the relief for the magnet.
The crankcase is a light press fit - no real force required, and has stood up to several hours of heavy gyroid infill pattern. Makes for convenient removal if you want to change up your rotor and crankcase covers. It's also relieved on the lower right to clear the Delta P style fan duct mod.
Print parts as pictured - the crankshaft will require a bit of support, I prefer snug. 3 perimeters is sufficient and fairly light infill will be fine, 15-20% range of your preferred pattern.
Glue the crankshaft to the end of the extruder motor shaft. Let dry.
Slip the rotor over the crankshaft with the teeth facing out. Gently guide the crankcase over the two, manipulating the rotor into position on the ‘sprocket’ of the inside crankcase. A pocket sized or similarly small screwdriver works well here.
The author remixed this model.