Cerberus the Humanoid Robot: Part I - Design

ABSTRACT The motive behind building humanoids is to design a robot that can duplicate the complexities of human motion, decision making, be able to help people and even accomplish tasks that cannot be carried out by humans. Building humanoids has always attracted scientists throughout the world but although the aim is seemingly simple, the task is never easy. In this series of articles, we are going to present the concept of a humanoid robot, named Cerberus, that walks like a biped and then switches its mode to a quadruped walker/crawler. In Part I, desirable system criteria, design alternatives, final design selection and kinematics of the robot are presented along with the humanoid robot’s simulations. Keywords Humanoid Robot, Cerberus Robot, Biped, Quadruped. 1. INTRODUCTION The motive behind building humanoids is simply to design a robot that can duplicate the complexities of human motion and genuinely help people. Although the motive is this simple, the task is never easy. For example it took Honda’s ASIMO more than 18 years of persistent study, research, and trial and error before Honda engineers achieved their dream of creating an advanced humanoid robot [1]. Walking process can be branched into two main groups as static and dynamic walking. Static walking in bipedal humanoids involves the complete shifting of the COG of the body over to the base foot area when the other is lifted to move forward. Such robots are designed and controlled from a kinematic standpoint (trajectory, or displacement-controlled), and as a consequence, they have relatively large feet and walk at a slow speed. A static-walking biped, such as the Honda P3 Humanoid, “does not move quite like people do and is energetically inefficient… it moves with a nonpendular appearance and uses about 2 kW during walking (Honda 2000), more than 20 times the muscle work rate of a walking human of the same size” [1]. Dynamic stability is needed to walk quickly and over varied terrains. The center of gravity lies outside the supporting leg base area during walking; the robot tumbles forward to its next step in dynamic equilibrium. Passive-dynamic walking can be a third group added to different type of walking process. Un-powered toy soldier or penguins were constructed as early as a century ago that would walk down a gentle incline without any motor control. Through the careful selection of the lengths and masses of their arms and legs, these toys maintain their balance while consuming very little energy (from gravity) when walking. Such models walk in a rigid manner, but their constructions are simple. Using this as the starting point, more DOF’s can be added, these being powered and controlled, a more fluid walking motion can be achieved. The aim for this study is toward the simple design that can do more functions. For this reason we selected a static walker with the capability of changing its mode from a biped to quadruped walker. The following section gives a brief history of the humanoid studies up to now. In the next section, various conceptual designs are introduced. Lastly, the final design concept selection procedure, detailed explanation of the final design and the preliminary gait definitions are presented.