Erect Wheel-Legged Stair Climbing Robot for Indoor Service Applications Ren C. Luo, Ming Hsiao, Tsung-Wei Lin Abstract—In this paper, an automatic erect stair climbing mobile robot is developed for indoor service applications. The design of high center of mass, tilt axis near ground, and the triangular wheel-legged structure enable the robot to climb stairs in a dynamic and self-balancing way. The wheel-legged mechanism also keeps the advantages of differential-wheeled mobile platforms when moving on flat ground, such as easy to control, saving power, and zero turning radius. Moreover, the overall mechanical design fits the requirements for a service robot to have proper height and small footprint, which can make human-robot interaction more natural and comfortable in indoor environment. Since the perceptual and control system of the robot are both well integrated, we successfully demonstrate the stair-climbing function and prove that the design and implementation of our work are feasible and efficient. As a result, the robot is expected to be a prototype of universal platform for indoor mobile service robots in the future. I. I NTRODUCTION A. Motivation and Related Works Since stair climbing is always a hot topic in robotics, various stair-climbing mechanisms, such as track-based [1][2], wheel-leg [3][4], or humanoid [5][6][7] solutions, are developed. However, for indoor service robots to perform tasks across floors, there are some requirements or limitations that those existed robot platforms cannot match. For example, to interact with human naturally, it is better for a service robot to have similar height as humans. And to move around indoor environment smoothly, the robot should have small footprint and high mobility. Unfortunately, those track-based stair-climbing robots usually lie on the floor, and the wheel-leg stair-climbing robots do not have small footprint or good mobility comparing to basic differential-wheeled platforms. Humanoid robots may be good solutions, but they are too complicated and waste much power for daily usages. Moreover, people would not like a service robot that can scratch or wear the edge of the steps while climbing stairs. As a result, we design a mobile robot (see Fig. 1) with proper locomotion and control strategy to meet all the requirements for stair-climbing service robots. Ren C. Luo is with the Center for Intelligent Robotics and Automation Research, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan 106 (corresponding author to provide phone: +886-2-3366-9822; e- mail: renluo@ntu.edu.tw). Ming Hsiao is with the Center for Intelligent Robotics and Automation Research, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan 106 (e-mail: mhsiao@ira.ee.ntu.edu.tw). Tsung-Wei Lin is with the Center for Intelligent Robotics and Automation Research, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, Taiwan 106 (e-mail: cwlin@ira.ee.ntu.edu.tw). Fig. 1. The general structure of the erect stair-climbing robot and the robot with a human rider standing on it There are several advantages of our robot. First, the robot can rotate a pair of triangular-shaped structures, each with three power wheels, to ascend or descend stairs step-by-step. Second, the robot can travel on flat ground just like differential-wheeled platforms. Third, the robot is high enough to have natural interaction with people, while the footprint of the robot is also small enough to pass through normal doorways. Moreover, the robot is designed to either move around and climb stairs automatically, or carry a rider who can control the robot. This makes the robot not only an independent mobile platform but also an accessible vehicle that can help a person move around in indoor environment. B. Structure of the Paper In this paper, we focus on the design of the robot and the locomotion strategy to ascend stairs. Next section describes the basic ideas and analysis of the robot, which help us to design and implement the mechanism, electrical system, and control strategy of the robot in Section III. Section IV shows the experimental results of the robot ascending stairs with some discussions. Section V is conclusion and future works. II. LOCOMOTION OF ASCENDING STAIRS A. Concepts As shown in Fig. 2, the concept of the method of stair climbing locomotion is that the robot can rotate a pair of triangular module (cyan) to climb up stairs and keep balance at the same time. The active wheels (green) on the vertices 2013 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) November 3-7, 2013. Tokyo, Japan 978-1-4673-6357-0/13/$31.00 ©2013 IEEE 2731