Abstract
To make a walking machine more active and practical, reducing its weight without reducing its working ability is the key issue of design. A robot with many actuators that produce a function of a real animal's joint-base kinematics tends to be too heavy for a light-step animal-like walking. In this paper we propose the concept of reducing the number of actuators, which is extremely effective for reducing the weight of a walker. Considering the essence of walking locomotion, absolutely indispensable functions are an arbitrary movement of a swinging leg and some translation of the center of gravity to maintain balance. Seven actuators for a biped, four for a quadruped, six for a hexapod are the minimum numbers for essential functions. A six-actuator hexapod is realized by trial manufacturing. Furthermore, as a practical solution, more reduction is available by restricting walking functions. A five-actuator biped and a three-actuator quadruped are introduced in the experiments.