edited by: Bruno Siciliano, Oussama Khatib
In this chapter, we introduce legged robots. After introducing the history of legged robot research in Sect. 16.1, we start to discuss hopping robots and analyze a simple passive walker as a typical cycling walking robot in Sect. 16.2; the Poincaré map is one of the most important tools to analyze its dynamics and stability. In Sect. 16.3, the dynamics and control of general biped robots are discussed. The key is the forward dynamics subject to the unilateral constraint between the feet and the ground. Its formal treatment leads to walking trajectory generation and various control methods. As a practical scheme to control biped robots, we discuss the zero-moment point (ZMP) in Sect. 16.4, including its definition, physical meaning, measurement, calculation, and usage. In Sect. 16.5, we move to multilegged robots. In this field, the most important subject is the relationship between gaits and stability. We also introduce the landmark robots in this field. In Sect. 16.6, we overview the divergence of the legged robots. We see leg–wheel hybrid robots, leg–arm hybrid robots, tethered walking robots, and wall-climbing robots. To compare these legged robots with different configurations, we use some useful performance indices such as the Froude number and the specific resistance, which are introduced in Sect. 16.7. We conclude the chapter and address future trends in Sect. 16.8.