[DIY] Split-Ring Dual Joined-Cycloids gear train - 3D Print

Unlike the Single Joined-Cycloids gear, a Dual Joined-Cycloids gear presents balanced centrifugal forces, and symmetrical forces on the stator and output rings, making it potentially more suited for high load torque and higher speed.

So I made this simple model to get familiar with its principle. It has a 105:1 reduction ratio, 3mm of eccentricity, and is 120mm wide.

The Fusion360 CAD model (very messy), STL, STEP and 3MF files are on Github and MakerWorld

Feel free to copy, remix, whatever (non-commercially) 

Happy printing to all !

 

  ______________________________________________


Sections:

  • Printing
  • Assembly
  • CAD
  • Diagram
  • Principle 
  • Resources  



Printing

 

Settings

  • 0.4mm nozzle, 0.24 layer height
  • 2 walls, 3 top, 2 bottom
  • 20% Support Cubic infill
  • Normal Auto support, 10° Threshold Angle
  • 0.5mm Support/object XY distance (easier to break supports free)




Assembly

 

Glue the shaft end on:


 Install the cycloidal pin-disc, dimple up, and the partial shaft:


Install the joined-cycloids, dimples up:

 

Glue the front pin-disc onto the pins, and glue on the front part of the shaft, ensuring that the dimples are all aligned: 


Glue the output hub to the wheel:


Install the output wheel and the front of the casing:



CAD


The cycloidal profiles were generated via a Fusion360 script from woodenCaliper on Github and with the help of this video from Howey 

Note that due to the usual Fusion360 Export bug when handling cycloidal surfaces, the discs had to be saved as STL files instead of the more desirable STEP format. 

 

Once again, shoutout to the extremely useful ME Virtuoso website where one can parametrically simulate their own planetary / wolfrom / cycloidal / harmonic / wave drives, and then download the STEP / DXF files. Some of which he also CNC'd or 3D printed, and tested on the ProMakina Youtube channel

 


Diagram

Note: showing a smaller output ring diameter, but can be = stator's
if the nb of pins is ≠ between the stator and output rings (like in this model)



Principle

 

The Dual Joined Cycloids is centrifugally balanced thanks to having 2 sets of discs 180° out of phase. When, say, one moves to the left, the other moves to the right. So their combined inertia, as experienced by the shaft, is zero (so long as their assembly weights are the same). Similar principle to a traditional Dual Cycloidal Disc drive.

 

Of note, the holes for the pins must have a diameter of Dpin + 4 x eccentricity, when a dual cycloidal disc drive only requires Dpin + 2 x eccentricity. Indeed, instead of just rotating concentrically on the shaft, the pin-disc is now one of the cycloidal discs. So it also has a 2_x_eccentricity wobble, thus requiring larger holes in the other disc for the pins. Consequently, it can be a challenge to add bearings in the holes and still have enough material left for disc and pin integrity.

 

 
Another design difficulty, is that the front or the back eccentric must be removable, to make installing the middle disc possible. To do that this model simply has a split shaft, but on an actual load-bearing drive this would likely be achieved via a removable eccentric or by using an eccentric bearing:
 
As for the other mechanical principles (direction, ratios, etc), they are the same as in the Single Joined-Cycloids gear train
 
Here Ns = 16 and No = 14. So, per the (Ns - 1) x No / (Ns - No) formula, it should result in a reduction ratio of 15 x 14 / 2 = 105:1, and a same-direction rotation. And, to my surprise, these predictions match the printed model. Hip hip hip hourra pour la science du dimanche 🥂 
 
 


Resources


I have not been able to find any research paper or documentation on this type of gear train. If anybody knows of any, could you drop a comment ?

 

This said, Paul Gould published a video on this drive, which he calls Dual Linked Two stage Cycloidal Gearbox

 

That's all folks !


   ______________________________________________
  
Posts in the Gear Train series:


Comments

Post a Comment