My Educational Mechanical Examples Series

This model is one of my educational mechanical mechanism examples on 80mm x 80mm base plates.
You can find all models of the series in this collection => [Mechanical Mechanism Examples]

The present model

This is an educational model of the Double Cardan Universal Joint.

Brief Description

A double-Cardan joint is a type of universal joint used to transmit rotational motion between two shafts that are not aligned in a straight line.

It consists of two Cardan joints connected in series, each using a cross-shaped component, commonly called a spider, to couple two intersecting shafts. A Cardan joint allows rotational motion to be transmitted smoothly at a wide range of crossing angles, as long as the angle is not too large.

However, in a single Cardan universal joint, the output shaft does not rotate at a constant speed even if the input shaft does. Its angular velocity oscillates periodically depending on the rotational angle, and the effect becomes more significant as the intersecting angle increases. An educational model of the single Cardan joint has been provided to illustrate this behavior.

In a double-Cardan joint, the two Cardan joints are arranged with mirror symmetry. Thus, although the intermediate yoke does not rotate at constant velocity, its speed fluctuations cancel out. As a result, the input and output shafts rotate at constant velocity.

Double-Cardan joints are widely used in automotive driveline systems.

Related Models

Case

This model is compatible with the case included in my first set.

Printing

• Use the models named ???-printable.stl for printing.
  The models named ???-assembled.stl are provided just to show how they should be assembled.
   
• Use well-dried PETG to have better dimensional accuracy.
• Use 0.1 mm or 0.08 mm layer height to have smoother surfaces.
• Use slow printing speed for overhangs.
• Select “Random” seam position to have smoother rotation.
  Randomly distributed seam should be easily worn out after some wearing.Printing

Sanding and Filing

Note that, in this model, the rotation of the bases for bearings is intentionally made not too smooth.

Sometimes, the gears suffer from the stringing effect and/or elephant foot effect, resulting in a too tight fit to the shafts (they are designed with a 0.15 mm radial clearance). 

If you see rough surface on the shafts due to stringing, sand off the roughness with a small piece of sand paper.

If you feel the gears do not rotate smoothly due to an elephant effect, widen the hole slightly by using a thin round bar file.

Without those issues, the parts should rotate very smoothly with minimal friction.

Assembly

Just snap assemble the parts.

Note that the flat sides of the spiders should face outward when they are assembled into the intermediate yoke.

Mounting the two shafts on the bearings is sometimes a little tricky because the bearing might be printed fragile if your filament has absorbed moisture. So, be careful not to break them when pushing the shafts in.

If your print shows stringing, it is a sign of highly moisturized filament.

Other examples

You may also be interested in the models in my educational mechanical mechanism examples.

Find them in this collection:
[https://makerworld.com/collections/15048577-my-educational-mechanism-models](https://makerworld.com/collections/15048577-my-educational-mechanism-models)

Happy printing!

Acknowledgement

I got into gears thanks to K.$uzuki's amazing articles and YouTube videos. Many of the mechanisms shown in this series came from the introductions on his website. He also makes excellent gear models himself. This series wouldn’t have existed without his inspiration.

I learned a lot about technical detail of designing gear tooth profiles from Haguruma-No-Hanashi website. I’m truly grateful for that.

License (2026-03-13 updated)

• The 3D model(s) are licensed under Creative Commons Attribution 4.0 International. (unchanged)
• However, the text and images on this page are copyright reserved. (added on 2026-03-13)