A mechanical system is often at the heart of a complete mechatronic design (a vehicle, a robot, an actuator…). Therefore, a fine modeling of the system’s mechanics is essential. We rely on the multibody approach, in which we have a longstanding expertise of more than two decades. We developed the ROBOTRAN software which is based on a symbolic approach, owing to flexibly export kinematic and dynamic models to dedicated environments, e.g. for optimization, design, sensitivity analysis and control. On top of that, we believe that the mechatronic approach does not only concern design or prototyping, but also multiphysics modeling. That discipline requires a good knowledge of the models inherent to the diverse fields being involved (mechanics, electromagnetism, hydraulic…) in order to provide a reliable and efficient global numerical model. This requires juggling with the different models (discrete, continuous, discretized – FEM, etc.) and determining the most relevant numerical interface, depending on the application.