For self-controlled endoscopes, many kinds of systems have been proposed. Among these, pneumatic actuators show significant potential. However, existing actuators, such as those used in endoscopes, have many weak points. In particular, free movement inside the human intestine is difficult because the diameter of the intestine varies dramatically along its length. We design and test a new method of locomotion of robotic endoscopes which allows safe manoeuverability in the human intestine. The actuating mechanism is composed of a solenoid at each end of the actuator and a single permanent magnet in the centre guide. If current is supplied to the two solenoids, attractive and repulsive forces occur between the permanent magnet and solenoid at each end. The permanent magnet moves by controlling the current supply period. When the current direction for operation is reversed, repulsive and attractive forces at each side are changed and the permanent magnet moves in the opposite direction. The collision at each period transfers momentum from the moving magnet to the actuator body. Furthermore, the moving speed of the actuator can be changed by the control of the impact force. Modelling and simulation are carried out to predict the performance of the actuator. The results of simulations are verified by comparison with experimental results. Finally, the momentum is measured by attaching an accelerometer to the solenoid head to define moving characteristics.