This paper presents the process of modelling a mechatronic system using two modelling methods. One the well known Matlab/Simulation package the other, Dynast, uses a novel energy based approach. The system modelled is a single axis positioning system driven via an armature controlled DC motor. The model consists of the main items in the system; pulse width modulated amplifier, DC motor, pulley and belt drive, and ball screw thread. Effects of inertia of parts and also frictional effects are also accoU;nted for in the models. The problems of combing different disciplines within each method are shown. Simulation results are presented from the two methods. Dynast was found to have significant advantages over Matlab.