Adding ros integrated contact sensors

Hello everyone! I'm building a biped model and I want to add a sensor that detects a collision between its foot and the ground and sends a message to a ROS topic. The 'Bumper controller' described [here](http://gazebosim.org/wiki/Tutorials/1.9/ROS_Motor_and_Sensor_Plugins) sounds pretty much like what I want. But when I try to put the following tag in the .gazebo file: true100test_bumperworld As suggested in the tutorial, I get the following error:> Error [Model.cc:761] Model[bumper_bot]> is attempting to load a plugin, but> detected an incorrect plugin type.> Plugin> filename[libgazebo_ros_bumper.so]> name[gazebo_ros_bumper_controller] I ftought it was because I did not specify any link for the sensor, so I tried using: This time I got the message: Error [parser.cc:697] XML Element[plugin], child of element[link] not defined in SDF. Ignoring.[link] Error [parser.cc:688] Error reading element Error [parser.cc:688] Error reading element Error [parser.cc:348] Unable to read element Error [parser.cc:299] parse as old deprecated model file failed. Error [World.cc:1469] Unable to read sdf string I also tried to follow [this](http://answers.ros.org/question/29158/how-do-i-use-force-sensor-bumper-sensor-in-gazebo/) answer, which suggested using a tag like this: base_link_geom20.0true20.0bumper This time the xml couldn't even be parsed. I did manage to add the gazebo contact sensor 100.000000base_link_collision/contact But it publishes to a gazebo topic, not a ROS topic. Does anyone know what am I doing wrong? I'm using gazebo 1.9.3 and ros-hydro. P.S: I've noticed the turtlebot has a sensor that does exactly what I want, but I couldn't figure out where to find the plugin which is used there or how to add it to my model. Thanks in advance!