Abstract Design of remote manipulators and industrial robot/manipulators requires the derivation of the inertia forces. They determine the forces produced on the arm, and consequently, the actuator torque and arm structure. A technique is developed for the determination of the dynamical forces with the help of point mass models. To this end, a generalized arm structure is introduced. This structure is decomposable in typical units, which represent the elements of a modular design and assembly system for robots and manipulators. Suggestions are made by two examples to assist the designer in obtaining good results.