Inverse Stability Analysis of a Biped Robot

This paper addresses the design and programming of a biped robot. Simple kinematics will be employed to carry out an analysis of biped stability and control. Center of mass and angular position are key components of successful motion. These variables are monitored throughout each process gait. The motion is simulated using COSMOSMotion. Different software packages found in the market are analyzed to show their capabilities to facilitate learning. MOTIVATION Understanding stability control for successful biped motion is a key component of robot design. Undergraduate programs in Mechanical Engineering emphasize the need to obtain continuous motion of the robot’s limbs. The analysis of dynamic motion of a biped robot is an arduous task usually expected from graduate students. Simple static analysis of the biped motion can be achieved by employing center of mass and force balance. The following paper is intended to assist future work in the University’s effort to improve its undergraduate robotics program as well as to facilitate future learning. BACKGROUND Perhaps one of the major discoveries in the 20 century has been robot locomotion. From automated production lines to simple daily use of electronics, robotics has helped revolutionize our daily lives. Recent attention has been diverted towards creating smart motion of smart human-like robots such as the robot THBIP-2, the second-generation biped of Tsinghua University [1]. Human-like robots are better known as humanoids. The bottom section of a humanoid, the biped, is one of the key components in achieving successful human-like motion. The fast advance in computer technology over the past decade has facilitated the development of biped robots. Different methods are used to design motion and stability of a biped. The two main areas of analysis are dynamic analysis and static analysis. Dynamic analysis employs the use of advanced system dynamic techniques; the Lagrange method could be considered a dynamic analysis [2]. Static analysis employs easier mathematics, mainly derived from geometrical and static relations. The use of dynamic models as well as static models has been enhanced by the increase in computational speed. Static analysis of biped stability is more practical for beginners in the area of robot design. One of the key challenges in using the method of static analysis is maintaining stability throughout the progress of each gait. BIPED DESCRIPTION Biped BRAT (Bipedal Robotic Articulating Transport) which is used in the project is a six Hitec HS-422 servo biped walker featuring three degrees of freedom (DOF) per leg. The biped is made from brushed aluminum servo brackets and includes an electronics carrier made from ultra-tough laser-cut Lexan. The robot is powered by a 6.0vdc Ni-MH 1600mAh battery pack. KINEMATIC ANALYSIS Optimal mass distribution is achieved by understanding the location of the center of mass [3]. According to the results presented, a cluster region of solutions is found when the function of (c, rgyr) approaches (l,0). The value c represents the distance of the center of mass measured from the floor. We can expect the system to reach a more balance position when this distance approaches the “l” length of the biped leg. We must also consider that the radius of gyration must also approach zero to obtain these desired conditions.