Toward efficient, fast, and versatile running robots based on free vibration

Despite the impressive demonstrations of energy efficient legged robots in the past, there are still a number of challenges remained to compete with legged locomotion of biological systems. In order to optimize energy efficiency of a legged robot, we typically need to sacrifice versatility: our robots have usually limited locomotion speed, lack of behavioral diversity, complex mechanical designs, and limited scalability in terms of weights and sizes [1, 2, 3]. From this perspective, we have been exploring an alternative design strategy of hopping/running robots that are not only simple and efficient, but also capable of exhibiting variations of locomotion behaviors.