Controllers

Install dependencies

In your home folder run the following command to install dependencies for ros controllers

sudo apt install ros-galactic-ros2-control ros-galactic-ros2-controllers ros-galactic-gazebo-ros2-control
sudo apt-get install ros-galactic-controller-manager

CMakeLists and Package XML

Add dependencies to CMakeLists

find_package(ros2_control REQUIRED)

Add dependencies to Package xml

<depend>ros2_control</depend>

URDF

Add the controllers for your joints.

 <ros2_control name="GazeboSystem" type="system">
 <hardware>
     <plugin>gazebo_ros2_control/GazeboSystem</plugin>
 </hardware>
 # Velocity Controllers

 <joint name="back_right_wheel_joint">
     <command_interface name="velocity">
         <param name="min">-1000.0</param>
         <param name="max">1000.0</param>
     </command_interface>
     <state_interface name="position"/>
     <state_interface name="velocity"/>
 </joint>

# Position Controller
 <joint name="front_left_axel_joint">
     <command_interface name="position">
         <param name="min">-3.14</param>
         <param name="max">3.14</param>
     </command_interface>
     <state_interface name="position"/>
     <state_interface name="velocity"/>
 </joint>

 </ros2_control>

You also need to add Gazebo Plugin for the Controller

<gazebo>
    <plugin filename="libgazebo_ros2_control.so" name="gazebo_ros2_control">
        <parameters>$(find test_package)/config/control.yaml</parameters>
    </plugin>
</gazebo>

In the parameters tag we need to pass a control.yaml file to setup the controllers.

Control Description

In the root of the package create a folder config.

mkdir config
cd config
touch control.yaml

Add this folder to the :guilabel::CMakeLists.txt file.

install(DIRECTORY
    urdf
    meshes
    launch
    worlds
    config
    DESTINATION share/${PROJECT_NAME}/
    )

You may edit the control.yaml file as follows to add controller description.

controller_manager:
    ros__parameters:
        update_rate: 1000  # Hz

        use_sim_time: true

        position_controller:
            type: position_controllers/JointGroupPositionController

        joint_state_broadcaster:
            type: joint_state_broadcaster/JointStateBroadcaster

        velocity_controller:
            type: velocity_controllers/JointGroupVelocityController



position_controller:
    ros__parameters:
        joints:
            - front_left_axel_joint
        interface_name: position
        command_interfaces:
            - position
        state_interfaces:
            - position
            - velocity


velocity_controller:
    ros__parameters:
        joints:
            - front_left_wheel_joint
        interface_name: velocity
        command_interfaces:
            - velocity
        state_interfaces:
            - position
            - velocity

You may now build and Overlay your package

Now launch the robot model.

Start the Controller

Run the following commands terminal to start the controllers.

ros2 control load_controller --set-state start joint_state_broadcaster

ros2 control load_controller --set-state start velocity_controller

ros2 control load_controller --set-state start position_controller

Publish commands

To publish the data to the joints use the following commands

ros2 topic pub /velocity_controller/commands std_msgs/msg/Float64MultiArray "{data: [1.0,-1.0,1.0,-1.0],layout: {dim:[], data_offset: 1"}}

ros2 topic pub /position_controller/commands std_msgs/msg/Float64MultiArray "{data: [0.3,0.3,0.3,0.3],layout: {dim:[], data_offset: 1"}}

Let’s add the controllers spawner into our launch files. To do this you can just import the revised tempplate for the launch folder in the root of your package using.

svn export https://github.com/shantanuparabumd/ENPM-662-Introduction-to-Robot-Modelling.git/trunk/templates/template3/launch