As the use of robotic mechanisms in various fields increases, the dynamics of many kinds of mechanism have to be thoroughly understood and analysed for safe and stable operation. This study is concerned with the enhancement of floor-driving ability for a two-wheeled inverted-pendulum-type autonomous vehicle. This type of robotic mechanism is innately unstable, therefore stabilization of the robot's body posture is primarily needed. For more stable driving at high speeds, the exact dynamics of this robotic mechanism was investigated using Kane's dynamic modelling. By analysing the dynamics and the system as a whole, the vehicle's stability at higher speeds was improved. The experimental results with various types of motion confirmed the enhancement of the robot's driving ability.