Simplicity in the dynamics model of a serial robot manipulator greatly enhances the speed of its control and the associated hardware implementation. Since the motion of one link influences the torque or force required at the other joints, the control becomes difficult. This is referred as dynamic coupling. In this paper, it is proposed to simplify the robot's dynamic coupling by suitably choosing the manipulator’s kinematic and dynamic parameters. The intention is to make the Generalized Inertia Matrix (GIM) of the serial manipulator associated with its dynamic equations of motion diagonal and/or constant. Such choice automatically ensures the associated convective inertia terms vanish. Such simplifications are carried out by investigating the expression of each element of the GIM. The concepts of the twist propagation matrices and the jointmotion propagation vectors are used to obtain the analytical expressions of the GIM elements that allow one to investigate the elements for simplifications. The methodology is illustrated with a 3-link spatial manipulator arm.