Controllers are unable to fight gravity in Gazebo simulation
I am currently trying to simulate a robot in Gazebo using the ROS framework. I used this (www.gazebosim.org/wiki/Tutorials/1.9/ROS_Control_with_Gazebo) Tutorial to get an existing robot model running with the controller from the ros_control package. Everything works fine, the controller for each joints are up and running. I can use the corresponding ROS topics to send commands to each controller.
There is one slight problem: The controllers are even unable to fight the robots own weight. No mather what combination of PID gains I set for the controller, the robot is always pulled down by its own weight.
I am using a UR5 robot for simulation, the URDF file can be found here (www.github.com/ros-industrial/universal_robot/tree/groovy-devel/ur_description).
Here are two screenshots of the simulation, one with gravity enabled:
www.s14.directupload.net/images/131214/u6f4585l.jpg
and one with gravity disabled:
www.s1.directupload.net/images/131214/oya39ubp.jpg
Can anyone help me here?