Modeling results are presented for a RALF (robotic arm, large and flexible) consisting of two ten-foot-long links and an actuator link that is parallel to the first link and drives the second link. A reduced-order model of the RALF system, which consists of the first two component modes of each link, was derived using the modal cost analysis approach. The original models are based on the first five component modes of each link. Two sets of mode shapes, which result from different boundary conditions on the components (links) are considered. The reduced-order model is optimal from the control point of view. The reduced-order model is evaluated by a comparison between the frequency responses and the modal cost analysis results. From the component cost calculation results, the modeling error ratio was found to have little variation, in spite of the change in angles of the joints.>