ros2_control Demos

This repository provides templates for the development of ros2_control-enabled robots and a simple simulations to demonstrate and prove ros2_control concepts.

Goals

The repository has three goals:

1. Implements the example configuration described in the ros-controls/roadmap repository file components_architecture_and_urdf_examples.
2. It provides templates for faster implementation of custom hardware and controllers;
3. The repository is a validation environment for ros2_control concepts, which can only be tested during run-time (e.g., execution of controllers by the controller manager, communication between robot hardware and controllers).

Description

The repository is inspired by the ros_control_boilerplate repository from Dave Coleman. The simulation has three parts/packages:

1. The first package, ros2_control_demo_bringup, holds launch files and runtime configurations for demo robots.
2. The second package, rrbot_description, stored URDF-description files, rviz configurations and meshes for the demo robots.
3. The third package, ros2_control_demo_hardware, implements the hardware interfaces described in the roadmap. The examples simulate a simple RRbot internally to provide sufficient test and demonstration data and reduce external dependencies. This package does not have any dependencies except ros2 core packages and can, therefore, be used on SoC-hardware of headless systems.

This repository demonstrates the following ros2_control concepts:

• Creating a *HardwareInterface for a System, Sensor, and Actuator.
• Creating a robot description in the form of URDF files.
• Loading the configuration and starting a robot using launch files.
• Control of two joints of RRBot.
• Using simulated robots and starting ros2_control with Gazebo simulator.
• Implementing a controller switching strategy for a robot.
• Using joint limits and transmission concepts in ros2_control.

Quick Hints

These are some quick hints, especially for those coming from a ROS1 control background:

• There are now three categories of hardware components: Sensor, Actuator, and System. Sensor is for individual sensors; Actuator is for individual actuators; System is for any combination of multiple sensors/actuators. You could think of a Sensor as read-only. All components are used as plugins and therefore exported using PLUGINLIB_EXPORT_CLASS macro.
• ros(1)_control only allowed three hardware interface types: position, velocity, and effort. ros2_control allows you to create any interface type by defining a custom string. For example, you might define a position_in_degrees or a temperature interface. The most common (position, velocity, acceleration, effort) are already defined as constants in hardware_interface/types/hardware_interface_type_values.hpp.
• Joint names in <ros2_control> tags in the URDF must be compatible with the controller's configuration.
• In ros2_control, all parameters for the driver are specified in the URDF. The ros2_control framework uses the <ros2_control> tag in the URDF.
• Joint names in <ros2_control> tags in the URDF must be compatible with the controller's configuration.

Build from source

git clone https://github.com/ros-controls/ros2_control
git clone https://github.com/ros-controls/ros2_controllers
git clone https://github.com/ros-controls/ros2_control_demos

NOTE: ros2_control and ros2_controllers packages are released for foxy and can be installed using a package manager. We provide officially released and maintained debian packages, which can easily be installed via aptitude. However, there might be cases in which not-yet released demos or features are only available through a source build in your own workspace.

• Install dependencies (maybe you need sudo):

  apt install ros-foxy-realtime-tools ros-foxy-xacro ros-foxy-angles
  

• Build everything, e.g. with:

  colcon build --symlink-install
  

• Do not forget to source setup.bash from the install folder!

Getting Started with ros2_control

Each of the described example cases from the roadmap has its own launch and URDF file.

Starting example robots

Each example is started with a single launch file which starts up the robot hardware, loads controller configurations and it also opens rviz2.

The rviz2 setup can be recreated following these steps:

• The robot models can be visualized using RobotModel display using /robot_description topic.
• Or you can simply open the configuration from rviz folder in rrbot_description package manually or directly by executing:

  rviz2 --display-config `ros2 pkg prefix rrbot_description`/share/rrbot_description/rviz/rrbot.rviz
  

RRBot, or ''Revolute-Revolute Manipulator Robot'', is a simple 3-linkage, 2-joint arm that we will use to demonstrate various features. It is essentially a double inverted pendulum and demonstrates some fun control concepts within a simulator and was originally introduced for Gazebo tutorials. The RRBot URDF files can be found in the urdf folder of rrbot_description package.

General notes about examples

1. To start an example open a terminal, source your ROS2-workspace and execute a launch file with:

   ros2 launch ros2_control_demo_bringup <example_launch_file>
   

2. To check if the hardware interface loaded properly, open another terminal and execute:

   ros2 control list_hardware_interfaces
   

   You should get something like:

   command interfaces
         joint1/position [unclaimed]
         joint2/position [unclaimed]
   state interfaces
         joint1/position
         joint2/position
   

3. Check which controllers are running using:

   ros2 control list_controllers
   

   You should get something like:

   forward_position_controller[forward_command_controller/ForwardCommandController] unconfigured
   joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster] active
   

4. Check Controllers and moving hardware section to move RRBot.

Example 1: "Industrial Robots with only one interface"

• Launch file: rrbot_system_position_only.launch.py
• Command interfaces:
  • joint1/position
  • joint2/position
• State interfaces:
  • joint1/position
  • joint2/position

Available controllers:

• joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster]
• forward_position_controller[forward_command_controller/ForwardCommandController] (position)

Available launch-file options:

• use_fake_hardware:=true - start FakeSystem instead of hardware. This is a simple simulation that mimics joint command to their states. This is useful to test ros2_control integration and controllers without physical hardware.

Example 2: "Industrial Robots with only one interface" (Gazebo simulation)

• TBA

Example 3: "Robots with multiple interfaces"

• Launch file: rrbot_system_multi_interface.launch.py
• Command interfaces:
  • joint1/position
  • joint2/position
  • joint1/velocity
  • joint2/velocity
  • joint1/acceleration
  • joint2/acceleration
• State interfaces:
  • joint1/position
  • joint2/position
  • joint1/velocity
  • joint2/velocity
  • joint1/acceleration
  • joint2/acceleration

Available controllers:

• joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster]
• forward_position_controller[position_controllers/JointGroupPositionController]
• forward_velocity_controller[velocity_controllers/JointGroupVelocityController]
• forward_acceleration_controller[forward_command_controller/ForwardCommandController]
• forward_illegal1_controller[forward_command_controller/ForwardCommandController]
• forward_illegal2_controller[forward_command_controller/ForwardCommandController]

Notes:

• The example shows how to implement multi-interface robot hardware taking care about interfaces used. The two illegal controllers demonstrate how hardware interface declines faulty claims to access joint command interfaces.

Example 4: "Differential drive mobile robot"

• Launch file: diffbot_system.launch.py
• Command interfaces:
  • left_wheel_joint/velocity
  • right_wheel_joint/velocity
• State interfaces:
  • left_wheel_joint/position
  • left_wheel_joint/velocity
  • right_wheel_joint/position
  • right_wheel_joint/velocity

Available controllers:

• joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster]
• diffbot_base_controller[diff_drive_controller/DiffDriveController] active

Sending commands to diff drive controller:

ros2 topic pub --rate 30 /diffbot_base_controller/cmd_vel_unstamped geometry_msgs/msg/Twist "linear:
 x: 0.7
 y: 0.0
 z: 0.0
angular:
 x: 0.0
 y: 0.0
 z: 1.0"

You should now see an orange box circling in rviz2.

Controllers and moving hardware

To move the robot you should load and start controllers. The JointStateController is used to publish the joint states to ROS topics. Direct joint commands are sent to this robot via the ForwardCommandController. The sections below describe their usage. Check the Results section on how to ensure that things went well.

JointStateController

Open another terminal and load, configure and start joint_state_controller:

ros2 control set_controller_state joint_state_controller start

Check if controller is loaded properly:

ros2 control list_controllers

You should get the response:

joint_state_controller[joint_state_controller/JointStateController] active

Now you should also see the RRbot represented correctly in rviz2.

Using ForwardCommandController

1. If you want to test hardware with ForwardCommandController first load a controller (not always needed):

   ros2 control load_controller forward_position_controller
   

   Check if the controller is loaded properly:

   ros2 control list_controllers
   

2. Then configure it:

   ros2 control set_controller_state forward_position_controller configure
   

   Check if the controller is loaded properly:

   ros2 control list_controllers
   

   You should get the response:

   forward_position_controller[forward_command_controller/ForwardCommandController] inactive
   

3. Now start the controller:

   ros2 control switch_controllers --start forward_position_controller
   

   Check if controllers are activated:

   ros2 control list_controllers
   

   You should get active in the response:

   joint_state_controller[joint_state_controller/JointStateController] active
   forward_position_controller[forward_command_controller/ForwardCommandController] active
   

4. Send a command to the controller, either:

   a. Manually using ros2 cli interface:

   ros2 topic pub /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data:
   - 0.5
   - 0.5"
   

   B. Or you can start a demo node which sends two goals every 5 seconds in a loop:

   ros2 launch ros2_control_demo_bringup test_forward_position_controller.launch.py
   

Result

1. Independently from the controller you should see how the example's output changes. Look for the following lines

   [RRBotSystemPositionOnlyHardware]: Got state 0.0 for joint 0!
   [RRBotSystemPositionOnlyHardware]: Got state 0.0 for joint 1!
   

2. If you echo the /joint_states or /dynamic_joint_states topics you should also get similar values.

   ros2 topic echo /joint_states
   ros2 topic echo /dynamic_joint_states
   

3. You should also see the RRbot moving in rviz2.