We are continually amazed by the things people do with LEGO and Technics, especially those that require incredible engineering skill. There’s an entire community based around building Great Ball Contraptions, which are LEGO Rube Goldberg machines that move tiny basketballs and soccer balls from one place to another. Except for a few rules about the input and output, the GBC horizons are boundless.
Famed GBC creator [Akiyuki] recently built a GBC module that’s designed to show the movement of strain wave gear systems. These types of gear systems are used in industrial applications where precision is vital. Strain wave gears are capable of reducing gear ratios in a small footprint.
There are three parts to a strain wave gear: the wave generator, the flex spline, and the circular spline. [Akiyuki]’s wave generator is the elliptical gray disk in the center. It is attached to the input shaft. The flex spline is the piece around the gray disk that is transporting the little balls. It is called a flex spline because the wave generator forces it to flex into an ellipse. Industrial strain wave gears are of course made of metal, and the flex spline does not get quite as deformed by the wave generator as this one. The 1/8 reduction ratio also exaggerates the deformation.
We covered one of [Akiyuki]’s larger GBCs a few years ago. While that one is definitely impressive, this strain wave gearing module is quite the engineering marvel.