In this paper a new approach based on the generalized momentum is used to obtain the dynamic model of a six degrees-of-freedom (dof) parallel manipulator. First, the system dynamic equations are obtained supposing the manipulator base platform is fixed. Afterwards, the dynamic model is extended to the case of a moving base platform. This could be important in a macro/micro robotic application, where a small manipulator is attached in series to a big manipulator. Simulation results of a macro/micro robotic system are presented and the contribution of the base platform motion to the total actuating forces is shown.