Walking robots are a lot of fun, and the idea of a walker that extends appendages on command from a basic shape — like a sphere — is an entertaining though mostly science fiction idea. The concept presents a variety of mechanical challenges in a restricted space, and while it certainly wasn’t easy, Gregory Leveque decided to make his own spheical quadruped.
The device uses a parallelogram servo-linkage system that enables each of the four legs to extend out of its shell and move up and down. A second servo for each leg is used to make them move forwards and backwards, producing a crawling motion seen in the video below. These legs not only fold up nicely when not being used, but another servo helps slide panels into place to cover the resulting gaps in the bottom for a very slick appearance. Notably, a flat area on the bottom keeps the sphere in an upright position when closed, so it likely won't be rolling into action before deploying its legs.
The build is controlled by an Arduino Nano along with a 16-channel servo driver. For navigation, it’s able to move the top part of the shell around, aiming an ultrasonic sensor to get readings about the surrounding environment. The root also features four addressable LEDs arranged around the middle of its circumference, creating an effect that is not essential to its operation, but “indispensable” according to Leveque. It’s a brilliantly executed idea, with a simple exterior that belies its intricate internals.