Cycloid Gear Library

This is a minimal library for the generation of cycloidical gears.
Some demo functions are included.

Required: OpenSCAD version >= 2015.03 !! MOST CURRENT VERSION HERE: https://github.com/mechadense/scad-lib-cyclogearprofiles
(old link) https://github.com/lsuess/scad-lib-cyclogearprofiles
usage: ... use // include would execute the demo modules

To get a cross-section of the desired gear invoke: cyclogearprofile(rtooth,nteeth,vpt,verbouse);

parameters:
– rtooth ... radius of gear teeth
– nteeth ... number of gear teeth
– vtp ... optional parameter -- vertices per tooth -- if left 0 (this is default) OpenSCADs resolution parameters $fa $fs or $fn will be applied.
– verbouse ... optional parameter -- If this is set bigger than zero then info about that gear will be reported under the choosen number.

To get a cross section of a rack invoke: cyclorackprofile(trackmin,rtooth,nteeth,teethshift0,vpt=0)

– trackmin ... thickness of rack at the thinnest points
– rtooth ... "radius" of gear teeth
– nteeth ... numbers of teeth of rack (smallest allowed unit is a quater of a full tooth cycle)
– teethshift0 ... at which quater to begin with the first tooth sensible are valued from the list: {-0.75,-0.5,0,+0.5,+0.75} all others have same effect
– vpt ...same as for cyclogearprofile

Alignment helper functions:

There are two helper functions to align gears. One for normal meshing an one for the case that one gear has the teeth inside (a concave gear) such that both gears turn in the same direction. alpha2(n1,n2,alpha1,beta12) // for normal meshing alpha2inroll(n1,n2,alpha1,beta12) // for gears rolling inside concave gears

parameters:
– _1 ... gear in origin; _2 ... meshed gear
– beta12 ... angle at which the meshed gear is located
– nX ... number of teeth of gear X
– alphaX ... rotation angle of gear X around its own origin

Extrusion helper functions:

If you want to make herringbone gears use this helper function. twistextrudegear(rtooth,nteeth,slant,nteethtwist) your_modified_cyclogearprofile(...);

The generated extrusion height (for nteethtwist=1) can be obtained with this helper function: extrudeheight1tooth(r,n,slantangle)

To twist over the angle of multiple teeth use nteethtwist > 1 & multiply nteethtwist to the return value of extrudeheight1tooth.

Further notes:

• The rolling radius of a cycloidical gear is two times the tooth number times the tooth radius. A helper function can be used to make code more self explanatory:

rollingradius(rtooth,nteeth)

• for cycloidical gears to mesh they need equal tooth radius
• I'd recommend to make herringbone gears instead of straight ones since staight cycloidical gears have varying axial force due to an osillating attack angle which can lead to bad vibrations under load.

Known issues

This library was written when OpenSCAD still had no support for higher order functions HOFs
(That is: Partially evaluated functions could not yet be handed over as function arguments)
This changed. OpenSCAD by now (since before 2023) supports HOFs and a new library with more features is in the works.

As a teaser: Expect:
– parametricity over tooth profiles
– addenda and dedenda of different cycloid rolling radii
– breakable edges
– projectability to various gemoetries (including bevel gears)
– generalization to cover both gears and screws

Category: Other