In this research, we study on posture control of a rotating link system with a torque unit under the condition of viscous friction. The torque unit is a module which consists of an electric motor and a reaction wheel. The friction arising from the presence of a viscous environment can not be ignored in the real system. We consider the influence of the viscous friction on the posture control of a one-link system. Then, we propose a control scheme that utilizes the viscous friction to achieve the posture control of the one-link system and the reaction wheel unloading. As a case study, we deal with a posture control problem of a water floating robot under the condition of viscous friction between the floating robot and the surrounding water. Then the effect of the proposed scheme is evaluated through several experiments.
