ROS2 Control Demos

This repository provides templates for the development of ros2_control-enabled robots and a simple simulation of a robot.

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_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.
2. The second package, ros2_control_demo_hardware_gazebo, uses a Gazebo simulator to simulate the RRBot and its physics. This package is useful to test the connection of ros2_control to the Gazebo simulator and to detect any missing plugins.
3. The third package ros2_control_demo_robot holds examples for RRbot URDF-description, launch files and controllers.

This repository demonstrates the following ros2_control concepts:

• Creating of *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 ros_control with Gazebo simulator
• Implementing of 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 interface: 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.
• 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.
• 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.
• <ros2_control> tags in the URDF must be compatible with the controller's configuration.
• PLUGINLIB_EXPORT_CLASS macro is required when implementing an interface.

Test of the Scenario Before the First Release

• Checkout ros-controls/ros2_control to get the core.

• Checkout ros-controls/ros2_controllers to get all the controllers.

• Checkout ros-controls/ros2_control_demos to get example hardware and robot launch files.

• 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.

Example 1: "Industrial Robots with only one interface"

1. Start the roslaunch file:

ros2 launch ros2_control_demo_robot rrbot_system_position_only.launch.py

2. Open another terminal and check if RRBotSystemPositionOnlyHardware is loaded properly:

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. Open another terminal and load, configure, and start controllers:

ros2 control load_start_controller joint_state_controller
ros2 control load_configure_controller forward_command_controller_position

Check if the controller is loaded properly:

ros2 control list_controllers

You should get the response:

joint_state_controller[joint_state_controller/JointStateController] active  
forward_command_controller_position[forward_command_controller/ForwardCommandController] inactive

4. Starting controller:

ros2 control switch_controllers --start-controllers forward_command_controller_position 

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_command_controller_position[forward_command_controller/ForwardCommandController] active

5. Open another terminal and send a message to the controller:

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

You should see how the example output changes. Look for the following lines

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

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

The other launch-files have corresponding names to their coresponding example. The URDF files can be found in the description folder.