I. Introduction
IN the past several years, there are several literatures to study the topic “two-wheeled robot”. The main topic of this research is how to keep the robot's balance. This system would become a primary tool for studying balance in active balancing system. It is also to be an important precursor to the field of legged machines and locomotion studies for robotics. There are many researches in this filed. In [1], a trajectory tracking algorithm based on a linear state space model was proposed to control mobile robot. Graser et al. [2] used Newtonian approach and linearization method to get a dynamic model to design a controller for a mobile. In [3], a dynamic model was derived with respect to the wheel motor torques as input while taking the nonholonomic no-slip constrains into considerations. Furthermore, two controllers were proposed to stabilize the vehicle's pitch and position. Until now, at least one commercial product is available such as “Segway”.