AbstractThis study aims to develop a methodology for parametric estimation of flexible manipulators considering an equivalent underactuated manipulator with passive joints, which should allow better possibilities to control flexible systems when addressing challenging problems to reach a satisfactory tracking motion. Theoretically, this is achieved by a minimum number of internal dynamics variables needed for representing almost all dynamics of the system. The parametric estimation approach is based on the optimal control theory considering a robust, stable method. This methodology requires only measured/computed data that are system output. Validation occurs through a virtual plant of the flexible manipulator observing a numerical perspective. The systems studied have serial and parallel kinematics and are mounted on carts for more diverse applications and general possibilities of the methodology.