A half-revolution mechanism is the one that can imitate the animal organs to generate asymmetry motion.It can be designed as a new type of propeller or turbine by high-speed fluid.A new type of transmission mechanism with internal cams and roller gear followers for the half-revolution device is discovered to overcome the disadvantage of the general transmission such as belts

chains or planet gears.Its construction and working principle are investigated.The parameters of the internal cam with roller gear followers are synthesized according to the requirement of the half-revolution mechanism.It can be modeled as a particular application of the parallel indexing cam mechanisms

where the internal cam is fixed and the frame is rotated and the roller gear follower moves in planet motion.The composition of the cam profile is proposed and the formula of the mechanism parameters is established by synthesis of its configuration and size.The equations for working profile and pressure angle of the cam are derived based on the inverse model and the derivative of pitch curve of cams.A visual prototype of the half-revolution mechanism is developed based on the determined parameters and derived equations by ADAMS.An example is given and demonstrates that it is available to design the new mechanism using the derived expressions.