Hi.
To close the issue, they are several way to do that:
- develop a "Gazebo plugin", which is a C++ calling Gazebo API (answer from iche033). The robot models do not need to be modified.
- use ROS and gazebo_ros_pkgs, in this case the URDF or SDF model should be adapted, w. <gazebo> tags and so on, as described in the gazebo-ROS tutorial
- player and do not know how the model should be modified
Thx all again.