By request of Syvwlch ( http://www.thingiverse.com/syvwlch ) and WilliamAAdams ( http://www.thingiverse.com/WilliamAAdams ), here is a stand-alone public-domain OpenSCAD cycloidal speed reducer. As with the Wankel Engine and Roots Blower I recently posted, this is intended more as an example of an interesting mechanism than as a practical device. If you want a practical printable speed reducer, you might consider one of the other alternatives like
the worm drives on this Tank http://www.thingiverse.com/thing:8080 or
differential planetary gears http://www.thingiverse.com/thing:7390 or
cascaded spur gears http://www.thingiverse.com/thing:7379 or
this planetary gear reducer http://www.thingiverse.com/thing:8460
There are several cycloidal-type mechanisms already on Thingiverse, such as
http://www.thingiverse.com/thing:3617 and http://www.thingiverse.com/thing:3736
There are also several interesting external sites like:
http://www.zincland.com/hypocycloid/
http://fabricationsofthemind.com/2010/07/09/extruder-design-1-printable-1001-hypocycloidal-gearbox/
https://github.com/triffid/Differential_Hypocycloid
http://reprap.org/wiki/Differential_Hypocycloid
http://en.wikipedia.org/wiki/Gerotor
http://en.wikipedia.org/wiki/Gear_pump
and many many interesting youtube videos such as
http://www.youtube.com/watch?v=bRn1K2XeWVE
http://www.youtube.com/watch?v=3WvPF6uGCq4
http://www.youtube.com/watch?v=CG2sPuqEXBg
http://www.youtube.com/watch?v=AMtyFwMDL7w
http://www.youtube.com/watch?v=h236SP86nnQ
This present script is based on a design by M.F. Hill described in his 1928 patent "Internal Rotor", number 1,682,563:
http://www.google.com/patents/about?id=mdF5AAAAEBAJ&dq=1682563
Note that this design is based on an offset hypocycloid, similar to Figure I in Hill's patent. Most of the contemporary designs appear to be based on an offset epicycloid, more closely resembling Figure V in the patent.
The motivated student can modify the code so it generates epicycloidal-based profiles. Hint: start by making a module ``epitrochoidBandFast(n, r, thickness, r_off)". The motivated student could also probably clean up my train-wreck of code and/or figure out how to do arrays in OpenSCAD.
Note also that these rotors can be used for pumps - see the gifs in the comments for an example.
| cycloidalGear.scad | 17.5KB | |
| cycloid_cover_plate.dxf | 24.7KB | |
| cycloid_cover_plate.stl | 285.9KB | |
| cycloid_driven_shaft.stl | 129.5KB | |
| cycloid_driven_shaft_1.dxf | 17.6KB | |
| cycloid_driven_shaft_2.dxf | 11.4KB | |
| cycloid_eccentric.stl | 49.0KB | |
| cycloid_eccentric_1.dxf | 4.4KB | |
| cycloid_eccentric_2.dxf | 4.3KB | |
| cycloid_inside_rotor.dxf | 27.2KB | |
| cycloid_inside_rotor.stl | 311.0KB | |
| cycloid_outside_rotor.stl | 755.8KB | |
| cycloid_outside_rotor_1.dxf | 40.7KB | |
| cycloid_outside_rotor_2.dxf | 24.8KB |
