Add docs on ROS 2 controllers

docs/tutorials/ros2.rst

@@ -17,3 +17,4 @@ Trossen Robotics supports the following ROS 2 distributions:
     ros2/description.rst
     ros2/bringup.rst
     ros2/moveit.rst
+    ros2/controllers.rst

docs/tutorials/ros2/controllers.rst

@@ -0,0 +1,50 @@
+=================
+ROS 2 Controllers
+=================
+
+A few controllers specific to Trossen Arm are provided in the ``trossen_arm_controllers`` package.
+These controllers provide extended functionality on top of standard ROS 2 controllers to expose features specific to Trossen Arm hardware.
+
+GravityCompensationController
+=============================
+
+The ``GravityCompensationController`` claims the external efforts interface of the arm's joints and commands 0.0Nm to each joint to enable gravity compensation.
+This allows the arm to be easily moved and held in place by an operator by hand.
+
+This controller can be demonstrated using the ``gravity_compensation.launch.py`` launch file in the ``trossen_arm_bringup`` package.
+
+.. code-block:: bash
+
+    source ~/ros2_ws/install/setup.bash
+    ros2 launch trossen_arm_bringup gravity_compensation.launch.py
+
+Once launched, gravity compensation mode will be activated and the arm should be easily movable by hand and will hold its position when released.
+
+CartesianPoseController
+=======================
+
+The ``CartesianPoseController`` allows commanding the end-effector of the arm to a desired pose in Cartesian space using inverse kinematics.
+This controller uses the Trossen Arm driver's built-in IK solver to compute joint positions for a desired end-effector pose.
+
+This controller can be demonstrated using the ``cartesian.launch.py`` launch file in the ``trossen_arm_bringup`` package.
+
+.. code-block:: bash
+
+    source ~/ros2_ws/install/setup.bash
+    ros2 launch trossen_arm_bringup cartesian.launch.py
+
+Once launched, the controller can be commanded by publishing a `geometry_msgs/PoseStamped <https://docs.ros2.org/latest/api/geometry_msgs/msg/PoseStamped.html>`_ message to the ``/cartesian_pose_controller/target_pose`` topic.
+A demonstration script is also provided in the ``trossen_arm_bringup`` package that sends a series of target poses to the controller.
+With the ``CartesianPoseController`` activated, the script can be run with the following command:
+
+.. code-block:: bash
+
+    source ~/ros2_ws/install/setup.bash
+    ros2 run trossen_arm_bringup cartesian_demo.py
+
+The script will send a series of target poses to the controller, moving the arm's end-effector through a sequence of positions in Cartesian space.
+
+.. Note::
+
+    The ``CartesianPoseController`` expects commands to be streamed to the controller at a high rate, else the arm may experience jittery motion.
+    For reference provided script commands poses at a rate of 200Hz.