This common toy actually demonstrates one of the biggest flaws of a well-known piece of modern machinery.
The cycloidal gearbox– whose most significant limitation is well-demonstrated by the beautiful patterns that the Spirograph creates.
Did you grow up using the Spirograph? It’s a tool for creating geometric art, pictured below. I remember being really impressed by how easy it is to create awesome, very mathematical-looking designs. 😊
The Spirograph and the cycloidal gearbox are very similar mechanisms. Each one has an external gear inside of an internal gear. The external gear (which is on the inside) moves, and the internal gear stays stationary. But the moving gear of the Spirograph highlights the eccentric motion, which causes the cycloidal gearbox to exhibit strong vibrations at high speed.
This is often mitigated by adding a second gear to cancel out the vibrations, but it’s not fully effective because it introduces rotational vibration instead of linear vibration.
Cycloidal gear boxes are very common, but they are not used for high speed applications for this reason. However, they have one of the best gear reduction to size ratios, making them a great compact option for gear motors in low speed applications.
Just an interesting observation I had this week and wanted to share, as a lot of us probably grew up using the Spirograph. It’s a great engineering lesson, in an everyday object, to show the young people in your life!
The Spirograph & The Cycloidal Gearbox
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