Wheeled mobile robots able to inspect pipe interior are usually used in industry. One of the major evaluations of these robots performance is mobility in limited spaces and special environments. Unanticipated area and obstacles along the robot path is one of the major challenges of robot success in missions. In this paper a novel module for increasing the robot traction when encountered small obstacles, paddle or large deposit is introduced. In addition, the mechanism increases the robot traction when move in high inclination pipes. The mechanism consists of two links mounted beside the four wheel drive robot. When the robot faces with an obstacle or a paddle and cannot move further, although robot wheels rotate, contacting the module’s links to pipe surface change the balance of normal forces applies between pipe and wheels. Further, when the links extend to contact upper part of pipe, it increases the wheels normal forces and provides a higher traction force consequently. Length of links may change in addition to its rotation. So, a two DOFs mechanism is provided which one motor is used as actuator. For switching active DOF, a locking mechanism is utilized using shape memory alloys actuators. The analysis and simulations show the capability of mechanism in increasing the robot traction. The mechanism performance is validated through ADAMS dynamic modeling software.