PR2_wrench_estimation

This ROS node uses the motor efforts in the arm and the error in
joint velocities to estimate the wrench (force/torque) applied to
the robot's end effector.

To run it:

 - Compile:
    rosmake pr2_wrench_estimation

 - Start it:
    roslaunch pr2_wrench_estimation launch/right_arm_wrench_estimation.launch
    roslaunch pr2_wrench_estimation launch/left_arm_wrench_estimation.launch

 - Check the scripts/ directory for examples of plotting functions, for example:
    rosrun pr2_wrench_estimation  plot_r_estimated_wrench.sh

   That shows a realtime graph of the estimated wrench. Pull the arm upwards,
   and you should see a big swing in the third graph (corresponding to the z
   coordinate) going up.

 
 - Important topics:
   /r_arm_wrench_estimation/estimated_wrench   <- 6DOF wrench estimation
   /r_arm_wrench_estimation/filtered_wrench  <- Filtered version of the previous topic

   /r_arm_wrench_estimation/twist_error <- 6DOF indication of the wrench based on joint velocity errors
   /r_arm_wrench_estimation/filtered_twist_error <- Filtered version of the prev. topic