The efforts in robotic devices simulation are constantly increasing in the latest years. A reliable and accurate dynamic simulator could improve the quality of the mechanical and controller design, while reducing the cost of development. Moreover, this tool should be independent from the specific robotic device and quite flexible and advanced to support the recent research on complex biologically inspired systems. Based on these considerations we evaluated the possibility to use OpenSim, a simulation tool for the biomechanical community, to implement robot dynamic simulations. OpenSim is a free software that provides a platform on which the biomechanics community can build and share libraries of human movement dynamic simulation. Currently, OpenSim is still not largely used in robotic. Nevertheless, it would have several advantages for the large libraries of tools and model of biological bodies. The tools to simulate the human movement could be used also in the simulation of the new generation of robots with variable stiffness and impedance actuators. So this work reports our first examples of robotic devices dynamic simulation using OpenSim. The obtained results and the interest of the OpenSim developers on our work encourage to follow this research direction.