144:1 Differential Cycloid Gearbox

This is a differential cyclodial gearbox which achieves a large ratio by a similar mechanism to the "split planetary" gearbox, but with far fewer and much less delicate parts.

With this large a gear reduction ratio, small & light "tin can" or "pancake" stepper motors, usually considered useless, may be useful for things like extruders. This one is designed to fit a PF-35T-48L4 motor I got from salvage. (Very similar one on SparkFun )

I did not want to put four little, fragile pins on the inside of the gear as pictured in most cycloidal solutions. It is designed so that the output is co-axial with the input, letting everything load-bearing easily sit on ball bearings.

It requires a few vitamins:

• 1 X 625 ball-bearing. (in diagram, pink)
• 2 X 12mm M3 screws and 2x M3 nuts to attach the input motor.
• 1 X M5 hex-head screw to fit in the output gear.
• 4 X 25mm M3 screws and nuts to attach the output to something

The "lemon shaped" mount fits only the pancake motor. The "turtle shaped" mount which sits atop fits the pancake motor with the two side screws and a NEMA17 flange with the other four. It is pictured attached to my Kossack extruder.

Differential Cycloid Gear Ratio

• a1, a2: Number of teeth on the lower gears
• b2, b2: Number of teeth on the upper gears

Not certain this formula is perfect, though it works for the situations I use it.

My design has 13 and 12 teeth on the lower gears, 12 and 11 teeth on the upper, which works out to 144:1.

 Name                           Last modified      Size  Description
 Parent Directory                                    -   
 hypo35.scad                    2017-01-09 20:24   12K  Complete Source Code
 hypo35.jpg                     2016-01-19 10:59   49K  144:1 Hypocycloid Gearbox
 hypo35-turtle.stl              2016-02-23 09:10  288K  Midsection fitting NEMA17
 hypo35-shaftpin.stl            2016-02-23 09:10   15K  Eccentric pin driven by motor
 hypo35-out.stl                 2016-02-23 09:10  241K  Output Gear
 hypo35-ecc.stl                 2016-02-23 09:10  394K  Eccentric driven by bearing
 hypo35-base.stl                2016-02-23 09:10  258K  Base which fits PM35 motor
 hypo35-assembled.jpg           2016-01-19 10:56   54K  144:1 Hypocycloid Gearbox
 dual-cycloid-ratio.gif         2016-02-04 10:18  941   Gear Ratio Formula
 cyclo.pl                       2017-01-10 16:41  274   Perl code to calculate ratio

Attribution

• Cycloid code is derived from mattmoses' Cyclodial Speed Reducer.
• Inspired by emmett's Differential Planetary Gearset