Problem with Gazebo's built-in PID controller.

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Hi, I using ROS fuerte version with Gazebo 1.0.2, my questions are:

1. When opening the Gazebo, there is some controller (PID) that is initialized automatically by default?
2. When creating a prismatic joint or the revolution Gazebo, is automatically added a controller (PID) in the joint?
3. Why the gains are limited at most 99,990 in "Control Joints"?
4. How to calculate the action applied to the joint using this controller's internal Gazebo?
5. In "Control Joints", the force, position and velocity are applied separately or is a summation?
6. There is documentation on this internal controller to the Gazebo?
7. What happens to the internal controller Gazebo when added a new controller?

My code URDF: https://gist.github.com/anonymous/6300846 and Image "Joint Control": http://postimg.org/image/a0dvyrsl7/

Thanks, best regards.