In this study an elastodynamic control system consisting of servomotor, elastic shaft, disc and elastic beam, which is attached to the disc, is considered. Non-dimensional parametric equations of motions are obtained. The control system damping ratio, the frequency ratio of the torsional natural frequency to the beam natural frequency and also the frequency ratio of the beam natural frequency to the control system frequency are used as parameters. Simulation results are obtained for the step response of the disc rotation and for the beam tip vibration for different frequency ratios. Results show that even for highly flexible systems the effect of flexibility on the control system behaviour can be substantially reduced by proper selection of the control system frequency. © IMechE 2004.