Skippy, the Balancing and Hopping Robot

Legged robots have gained popularity recently, with quadrupeds being sufficiently reliable to leave the research labs and be deployed in real-world environments. Humanoids, on the other hand, still need to be developed more, and extensive research in the field of legged robots is still required. This thesis presents Skippy, a highly athletic, underactuated balancing and hopping monopedal robot. Skippy is a simple robot with only one leg and two actuators, and although its design is simple, complex dynamics govern it. Due to its intrinsic instability, it is difficult to control, making it a suitable testing machine for novel balancing and hopping control algorithms. The beginning of this work focuses on the experimental validation of robotic hardware and software. It proposes a methodology to verify the correct behaviour of Skippy's sensorimotor system in all the possible scenarios it can encounter while operating (e.g. continuous hopping, crash landing after a wrong manoeuvre) through purpose-built testing apparatus. Furthermore, it presents the intermediate 2D balancing machines built before Skippy to validate the correct behaviour of the aforementioned sensorimotor system while balancing using Featherstone's balance controller. Then, the research described in this thesis extends Featherstone's balance controller to the case of a robot balancing on a rolling contact rather than on a single-contact point foot, and it validates it with an experiment on a purpose-built balancing machine. At last, this work shows Skippy in its 2D-constrained version, proving the robot's capability as a balancing and hopping machine.