This is a ROS 2 package for integrating the ros2_control controller architecture with the Gazebo simulator.

This package provides a Gazebo plugin which instantiates a ros2_control controller manager and connects it to a Gazebo model.

This repository contains the contents for testing gazebo_ros2_control

It is running Gazebo and some other ROS 2 nodes.

cd Docker
docker build -t gazebo_ros2_control .

Docker allows us to run the demo without GUI if we don't configure it properly. The following command runs the demo without GUI:

docker run -it --rm --name gazebo_ros2_control_demo --net host gazebo_ros2_control ros2 launch gazebo_ros2_control_demos cart_example_position.launch.py gui:=false

The in your local machine you can run the Gazebo client:

gzclient

To run the demo with GUI we are going to use rocker which is a tool to run docker images with customized local support injected for things like nvidia support. And user id specific files for cleaner mounting file permissions. You can install this tool with the following instructions.

The following command will launch Gazebo:

rocker --x11 --nvidia --name gazebo_ros2_control_demo gazebo_ros2_control:latest

The following commands allow to move the cart in the rail:

docker exec -it gazebo_ros2_control_demo bash
source /home/ros2_ws/install/setup.bash
ros2 run gazebo_ros2_control_demos example_position

To use ros2_control with your robot, you need to add some additional elements to your URDF. The <transmission> element is used to link actuators to joints, see the <transmission> spec for exact XML format.

For the purposes of gazebo_ros2_control in its current implementation, the only important information in these transmission tags are:

• <joint name=""> the name must correspond to a joint else where in your URDF
• <type> the type of transmission. Currently only transmission_interface/SimpleTransmission is implemented.
• <hardwareInterface> within the <actuator> and <joint> tags, this tells the gazebo_ros2_control plugin what hardware interface to load (position, velocity or effort interfaces).

In addition to the transmission tags, a Gazebo plugin needs to be added to your URDF that actually parses the transmission tags and loads the appropriate hardware interfaces and controller manager. By default the gazebo_ros2_control plugin is very simple, though it is also extensible via an additional plugin architecture to allow power users to create their own custom robot hardware interfaces between ros2_control and Gazebo.

<gazebo>
    <plugin filename="libgazebo_ros2_control.so" name="gazebo_ros2_control">
      <robot_sim_type>gazebo_ros2_control/DefaultRobotHWSim</robot_sim_type>
      <robot_param>robot_description</robot_param>
      <robot_param_node>robot_state_publisher</robot_param_node>
      <parameters>$(find gazebo_ros2_control_demos)/config/cartpole_controller.yaml</parameters>
      <e_stop_topic>False</e_stop_topic>
    </plugin>
</gazebo>

The gazebo_ros2_control <plugin> tag also has the following optional child elements:

• <control_period>: The period of the controller update (in seconds), defaults to Gazebo's period
• <robot_param>: The location of the robot_description (URDF) on the parameter server, defaults to robot_description
• <robot_param_node>: Name of the node where the robot_param is located, defauls to robot_state_publisher
• <robot_sim_type>: The pluginlib name of a custom robot sim interface to be used, defaults to gazebo_ros2_control/DefaultRobotHWSim
• <parameters>: YAML file with the configuration of the controllers

By default, without a <robot_sim_type> tag, gazebo_ros2_control will attempt to get all of the information it needs to interface with a ros2_control-based controller out of the URDF. This is sufficient for most cases, and good for at least getting started.

The default behavior provides the following ros2_control interfaces:

• hardware_interface::JointStateInterface
• hardware_interface::EffortJointInterface
• hardware_interface::VelocityJointInterface

The gazebo_ros2_control Gazebo plugin also provides a pluginlib-based interface to implement custom interfaces between Gazebo and ros2_control for simulating more complex mechanisms (nonlinear springs, linkages, etc).

These plugins must inherit gazebo_ros2_control::RobotHWSim which implements a simulated ros2_control hardware_interface::RobotHW. RobotHWSim provides API-level access to read and command joint properties in the Gazebo simulator.

The respective RobotHWSim sub-class is specified in a URDF model and is loaded when the robot model is loaded. For example, the following XML will load the default plugin (same behavior as when using no <robot_sim_type> tag):

<gazebo>
  <plugin name="gazebo_ros2_control" filename="libgazebo_ros2_control.so">
    <robot_sim_type>gazebo_ros2_control/DefaultRobotHWSim</robot_sim_type>
  </plugin>
</gazebo>

Use the tag <parameters> inside <plugin> to set the YAML file with the controller configuration.

<gazebo>
  <plugin name="gazebo_ros2_control" filename="libgazebo_ros2_control.so">
    <parameters>$(find gazebo_ros2_control_demos)/config/cartpole_controller.yaml</parameters>
  </plugin>
<gazebo>

This controller publishes the state of all resources registered to a hardware_interface::JointStateInterface to a topic of type sensor_msgs/msg/JointState. The following is a basic configuration of the controller.

joint_state_controller:
  ros__parameters:
    type: joint_state_controller/JointStateController
    publish_rate: 50

This controller creates an action called /cart_pole_controller/follow_joint_trajectory of type control_msgs::action::FollowJointTrajectory.

cart_pole_controller:
  ros__parameters:
    type: joint_trajectory_controller/JointTrajectoryController
    joints:
       - slider_to_cart
    write_op_modes:
       - slider_to_cart
    state_publish_rate: 25
    action_monitor_rate: 20
    constraints:
      stopped_velocity_tolerance: 0.05
      goal_time: 5

To set the PID gains for a specific joint you need to define them inside <plugin><ros></plugin></ros>. Using the generic way of defining parameters with gazebo_ros. The name of the parameter correspond the name of the joint followed by a dot and the name of the parameter: p, i, d, i_clamp_max, i_clamp_min and antiwindup.

<gazebo>
  <plugin filename="libgazebo_ros2_control.so" name="gazebo_ros2_control">
    <ros>
      <namespace>/my_robot</namespace>
      <parameter name="slider_to_cart.p" type="double">50.0</parameter>
      <parameter name="slider_to_cart.i" type="double">10.0</parameter>
      <parameter name="slider_to_cart.d" type="double">15.0</parameter>
      <parameter name="slider_to_cart.i_clamp_max" type="double">3.0</parameter>
      <parameter name="slider_to_cart.i_clamp_min" type="double">-3.0</parameter>
      <parameter name="slider_to_cart.antiwindup" type="bool">false</parameter>
      <remapping>e_stop_topic:=emergency_stop</remapping>
    </ros>
    <robot_sim_type>gazebo_ros2_control/DefaultRobotHWSim</robot_sim_type>
    <parameters>$(find gazebo_ros2_control_demos)/config/cartpole_controller.yaml</parameters>
    ...
  </plugins>
</gazebo>

There are some examples in the gazebo_ros2_control_demos package. These examples allow to launch a cart in a 30 meter rail.

You can run some of the configuration running the following commands:

ros2 launch gazebo_ros2_control_demos cart_example_position_pid.launch.py
ros2 launch gazebo_ros2_control_demos cart_example_position.launch.py
ros2 launch gazebo_ros2_control_demos cart_example_velocity.launch.py

Send example commands:

When the Gazebo world is launched you can run some of the following commads to move the cart.

ros2 run gazebo_ros2_control_demos example_position
ros2 run gazebo_ros2_control_demos example_velocity

To get or modify the values of the PID controller you can run the following commands:

ros2 param get /gazebo_ros2_control slider_to_cart.p
ros2 param get /gazebo_ros2_control slider_to_cart.i
ros2 param get /gazebo_ros2_control slider_to_cart.d
ros2 param get /gazebo_ros2_control slider_to_cart.i_clamp_max
ros2 param get /gazebo_ros2_control slider_to_cart.i_clamp_min

ros2 param set /gazebo_ros2_control slider_to_cart.p 50.0
ros2 param set /gazebo_ros2_control slider_to_cart.i 10.0
ros2 param set /gazebo_ros2_control slider_to_cart.d 15.0
ros2 param set /gazebo_ros2_control slider_to_cart.i_clamp_max 3.0
ros2 param set /gazebo_ros2_control slider_to_cart.i_clamp_min -3.0

ros2_control and ros2_controllers are in a redesign phase. Some of the packages are unofficial. In the following links you can track some of the missing features.

• ros-controls/ros2_control#26
• ros-controls/ros2_control#32