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Running the Controller

Description: Explains how to download the action server and controller and how to run a force controlled trajectory.

Keywords: force, compliance, stiffness, controller, pr2 arms

Tutorial Level: INTERMEDIATE

Next Tutorial: Writing a Force Controller

If you have not already, you must first download the ee_cart_imped stack.

Updating the Controller and Action Files

Since the controller and action are not kept within the ROS stacks, you should update them manually to ensure you have the most recent version:

roscd ee_cart_imped_control
svn update
roscd ee_cart_imped_action
svn update

Compiling

First, open a new shell and change to the directory you created in the last tutorial:

roscd ee_cart_imped_tutorial

When you created the package, the default CMakeLists.txt was created. Open it up and add the following line at the bottom

rosbuild_add_executable(stiffness_control src/stiffness_control.cpp)

Now rosmake the package

rosmake ee_cart_imped_tutorial

This should also compile the ee_cart_imped_control and ee_cart_imped_action packages.

Starting the Controller and Action Server

If you are working in simulation, open a new shell and run

roslaunch pr2_gazebo pr2_empty_world.launch

If you are working on the PR2, restart the robot using the -e option

sudo robot start -e

This option assumes the environment is set and therefore does not overwrite your environment. It is essential when using a non-standard controller. If you fail to start the robot with the -e option, ROS will be unable to find the controller type.

Once the simulator is up or the robot is restarted, in a new shell type

roslaunch ee_cart_imped_action r_arm_cart_imped_action.launch

This stops the usual controller for the right arm and starts the ee_cart_imped controller and action server for the right arm. To use the controller for the left arm, look at the ee_cart_imped_action/launch/l_arm_cart_imped.launch file. To launch the controller for both arms, you can use the ee_cart_imped_action/launch/ee_cart_imped_action.launch file.

The ee_cart_imped controller is now running in the right arm. At present, the controller is attempting to hold the end effector at a constant Cartesian point. If you are working with the PR2, you can test if the new controller is indeed controlling the right arm by manipulating the arm joints without moving the end effector. Unlike under the standard controller (which should still be running on the left arm for comparison), so long as the end effector does not move, there should not be much resistance to moving the other joints:

Running the Trajectory

Now you can try running the example we created. In a new shell type

rosrun ee_cart_imped_tutorial stiffness_control

You should see the trajectory execute.

If you are working on the PR2, the last point will be held. This means there will still be a light stiffness in the x direction. This should be very noticeable if you attempt to move the PR2 gripper. It will be easy to move it in the x direction (towards or away from the robot), but hard to move in any other direction or to turn.

Force Control

Now that we have written and run a stiffness controller, we can use the ee_cart_imped_control package to also run a force-controlled trajectory.