Advanced Robotics, Vol. 21, No. 3–4, pp. 461–484 (2007)  VSP and Robotics Society of Japan 2007. Also available online - www.brill.nl/ar Full paper Experimental realization of dynamic walking for a human-riding biped robot, HUBO FX-1 JUNG-YUP KIM, JUNGHO LEE and JUN-HO OH ∗ HUBO Laboratory, Humanoid Robot Research Center, Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 373-1 Guseong-dong Yuseong-gu, Daejeon 305-701, South Korea Received 2 May 2006; accepted 2 August 2006 Abstract—This paper describes a control strategy of the stable walking for the human-riding biped robot, HUBO FX-1. HUBO FX-1 largely consists of two legs with 12 d.o.f., a pelvis and a cockpit. A normal adult can easily ride on HUBO FX-1 by means of a foothold, and can change the walking direction and speed continuously through the use of a joystick. Principally, this kind of robot must be able to carry a payload of at least 100 kg in order to carry a person easily. A sufficient payload can be accomplished by two ways. The first is through the choice of a highly efficient actuator. The second is through weight reduction of the robot body frames. As an efficient actuator, a high-power AC servo motor and a backlash-free harmonic drive reduction gear were utilized. Furthermore, the thickness and the size of the aluminum body frames were sufficiently reduced so that the weight of HUBO FX-1 is light enough. The disadvantage of the weight reduction is that HUBO FX-1 was not able to walk stably due to structural vibrations, as the body structures become more flexible due to this procedure. This problem was solved through the use of a simple theoretical model and a vibration reduction controller based on sensory feedback. In order to endow the robot with a stable biped walking capability, a standard walking pattern and online controllers based on the real-time sensory feedback were designed. Finally, the performance of the real-time balance control strategy was experimentally verified and stable dynamic walking of the human-riding biped robot, HUBO FX-1, carrying one passenger was realized. Keywords: Human-riding biped robot; real-time balance control; HUBO FX-1. 1. INTRODUCTION Research concerning biped walking robots has been conducted largely in Japan since the 1970s. Biped walking robots have since grown into biped humanoid robots due to breakthroughs in the fundamentals and in related areas of high technology in the late 20th century. The biped humanoid robot has been recognized as a ∗ To whom correspondence should be addressed. E-mail: jhoh@kaist.ac.kr