Most of them end up attaching a gearbox to an off-the-shelf brushless motor and call it a day. Not everyone goes that way, though, which is why this internal cycloidal drive actuator caught our eye.

We’ve seen similar drives recently in [Paul Gould]’s 3D Printed Robot Actuator which uses a cycloidal gearbox, as well as the incredibly smooth action of the cycloidal drive-inspired Abacus Drive.

Wren proved that the length of a cycloid arch is four times the diameter of the circle that generates it. Today, this is an easy problem in integral calculus but in 1658 it was a formidable ...