Yamagata University developed the so-called “Cross Spherical Gear”, which is known for its unusual range of motion. It is a spatially curved gear that enables movement in several axes and is suitable for simulating complex joint movements. British YouTuber Robert Murray-Smith has now constructed a functional replica of this gearbox that can be produced using standard 3D printers. He has made the corresponding 3D model available for free on Thingiverse.
The gearbox consists of three parts: an upper and a lower half-shell and a connecting element. It was produced in Tinkercad by rotating a basic gearwheel in two axes step by step. Repeated copying and rotation of the gearwheel by one degree at a time creates a spherical structure with offset tooth flanks. This allows the typical sliding and rotating movement.
After cutting the structure on one side, the model is further processed and divided into several segments. Additional dowel pins and rotationally symmetrical recesses ensure precise alignment of the individual parts during subsequent assembly. Robert Murray-Smith also developed a simple drive solution. A slightly helical gear rim engages via another gear wheel and transmits the movement to the curved gear wheels.
Commercially available 22 mm skateboard ball bearings are used for the bearings, which are pressed into the recesses provided. The entire construction is modular and allows easy assembly and disassembly.
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