I. Introduction
Self-balancing personal mobility (SBPM), a battery-powered eco-friendly personal transportation means, is steadily expanding in the market [1]. Although SBPM market growth is predicted, relevant safety regulations and safety requirements are not yet clearly established. Under this circumstance, related accidents are increasing every year. Most of the research related to the SBPM so far have been mainly concerned with the controller design to improve driving performance [2], [3], [4], [5], while the development of test methods and indices necessary for the evaluation of safety/stability [6], [7], [8], [9] are limited. Some related research has been reported [10], [11], [12], [13]. However, they approached with qualitative assessment, such as rider questionnaire and interviews, rather than measuring physical data. Therefore, it was difficult to identify physical causality of the accidents, and objectivity of the results could not be guaranteed. Castro [14] modeled a human rider as a rigid body but human rider’s behavior that affects the safety of the SBPM directly could not be realized correctly with it.