Hey! This thing is still a Work in Progress. Files, instructions, and other stuff might change!

Nema17 Differential Planetary Gear

by SimCity Mar 9, 2013
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While this would be no use for the axes on your 3D printer (due to minimum extrusion speed), it would be amazingly useful for the main spindle on an eggbot. The torque multiplication may even add enough strength to use it as a lathe. I only have an old 3 deg/step motor on hand to build one for my hackerspace and have been putting it off since the resolution would be too poor. If this prints decently it'll be worth making now.

Do you think this homeprinted gears would be precise enough to make the z-axis steps on a reprap type printer smaller?

depends on how low you can get with the tolerance. Honestly though my rep rap is currently at 3200 steps per mm without any gearing, using this to gear it down further would be 185600. it would take forever to move the z axis... that and its so fine you would never use it, cause you cant drop the flow rate of the extruder beyond a certain point

This looks great -- I was looking for a way to achieve gear reduction in a small package for a stepper (trying to build an improved bowden extruder). One thing I noticed -- I don't think this is going to work without a fixed planet carrier, as the planets will simply spin around instead of rotating the output shaft. That said, it should be quite simple to make one.
That said i'm printing one right now and I'll try a few things with it once it's done.