Creating a Simple Teleoperation System with ROS 2 🎯

Ever dreamed of controlling a robot from afar? ✨ With the Robot Operating System (ROS) 2, that dream can become a reality! This tutorial will guide you through building a simple ROS 2 Teleoperation System, allowing you to remotely control a robot’s movements. We’ll cover everything from setting up your ROS 2 environment to writing the necessary Python code. Get ready to dive in and unlock the power of remote robotics!

Executive Summary

This article provides a comprehensive guide to creating a basic teleoperation system using ROS 2. We’ll explore the fundamental concepts of ROS 2, including nodes, topics, and message types. You will learn how to implement a simple controller to drive your robots remotely. The tutorial covers setting up the ROS 2 environment, creating custom message types for teleoperation commands, writing Python nodes for reading input (e.g., keyboard commands) and controlling the robot, and testing the system. By following this guide, you’ll gain a solid understanding of teleoperation principles and practical experience with ROS 2, enabling you to build more complex robotic control systems in the future. This project provides a stepping stone to more advanced robotics applications, fostering innovation and accessibility within the field.

Setting up Your ROS 2 Environment

Before we begin, you’ll need a working ROS 2 environment. This involves installing ROS 2 and setting up your workspace. Let’s walk through the essentials.

• Install ROS 2: Follow the official ROS 2 installation instructions for your operating system (Ubuntu is commonly used). You can find them on the ROS 2 website.
• Create a ROS 2 Workspace: A workspace is where you’ll store your ROS 2 packages. Use the following commands in your terminal:

  mkdir -p ros2_ws/src
  cd ros2_ws
  ros2 pkg create --build-type ament_python my_teleop_pkg --dependencies rclpy geometry_msgs

• Source the ROS 2 Environment: Each time you open a new terminal, you need to source the ROS 2 environment:

  source /opt/ros/humble/setup.bash  # Or your ROS 2 version
  source install/setup.bash

• Verify the Installation: Run a simple ROS 2 command to ensure everything is working:

  ros2 run turtlesim turtlesim_node

Creating Custom Message Types for Teleoperation

To send teleoperation commands to the robot, we’ll define a custom message type. This allows us to specify the desired robot velocity.

• Define the Message: Create a `Teleop.msg` file in your `my_teleop_pkg/msg` directory. Here’s an example:

  # my_teleop_pkg/msg/Teleop.msg
  float64 linear_velocity
  float64 angular_velocity

• Update `package.xml`: Add the necessary dependencies to your `package.xml` file:

   <buildtool_depend>ament_cmake</buildtool_depend>
    <build_depend>rosidl_default_generators</build_depend>
    <exec_depend>rosidl_default_runtime</exec_depend>
    <member_of_group>rosidl_interface_files</member_of_group>

• Update `CMakeLists.txt`: Configure CMake to generate the message interfaces:

  find_package(rosidl_default_generators REQUIRED)
  
  rosidl_generate_interfaces(${PROJECT_NAME}
    "msg/Teleop.msg"
    DEPENDENCIES geometry_msgs
  )

• Build the Package: From your workspace root, build the package:

  colcon build

• Source the Workspace Again: Don’t forget to source the workspace after building.

  source install/setup.bash

Writing the Teleoperation Node (Python)

Now, let’s create a Python node that reads keyboard input and publishes the teleoperation commands using our custom message type.

• Create the Python Script: Create a file named `teleop_node.py` in the `my_teleop_pkg/my_teleop_pkg` directory.
• Implement the Node: Here’s a sample script:

  # my_teleop_pkg/my_teleop_pkg/teleop_node.py
  import rclpy
  from rclpy.node import Node
  from my_teleop_pkg.msg import Teleop
  import sys
  
  class TeleopNode(Node):
      def __init__(self):
          super().__init__('teleop_node')
          self.publisher_ = self.create_publisher(Teleop, 'teleop_commands', 10)
          timer_period = 0.1  # seconds
          self.timer = self.create_timer(timer_period, self.timer_callback)
          self.linear_velocity = 0.0
          self.angular_velocity = 0.0
  
      def timer_callback(self):
          msg = Teleop()
          msg.linear_velocity = self.linear_velocity
          msg.angular_velocity = self.angular_velocity
          self.publisher_.publish(msg)
          #self.get_logger().info('Publishing: Linear: %f, Angular: %f' % (msg.linear_velocity, msg.angular_velocity))
  
  
  def main(args=None):
      rclpy.init(args=args)
      teleop_node = TeleopNode()
  
      print("Use 'w', 'a', 's', 'd' to control the robot.")
      print("Press 'q' to quit.")
  
      try:
          while rclpy.ok():
              rclpy.spin_once(teleop_node)
              char = input("Enter command: ")
              if char == 'w':
                  teleop_node.linear_velocity = 0.5
                  teleop_node.angular_velocity = 0.0
              elif char == 's':
                  teleop_node.linear_velocity = -0.5
                  teleop_node.angular_velocity = 0.0
              elif char == 'a':
                  teleop_node.linear_velocity = 0.0
                  teleop_node.angular_velocity = 0.5
              elif char == 'd':
                  teleop_node.linear_velocity = 0.0
                  teleop_node.angular_velocity = -0.5
              elif char == 'q':
                  break
              else:
                  teleop_node.linear_velocity = 0.0
                  teleop_node.angular_velocity = 0.0
  
  
      except KeyboardInterrupt:
          pass
  
      teleop_node.destroy_node()
      rclpy.shutdown()
  
  
  if __name__ == '__main__':
      main()
  

• Make the Script Executable:

  chmod +x my_teleop_pkg/my_teleop_pkg/teleop_node.py

• Update `setup.py`: Add the script to the entry points in `setup.py`:

  entry_points={
          'console_scripts': [
              'teleop_node = my_teleop_pkg.teleop_node:main',
          ],
      },

• Rebuild the Package:

  colcon build

• Source the Workspace Again:

  source install/setup.bash

Creating a Robot Control Node (Python)

This node subscribes to the `teleop_commands` topic and controls the robot’s movement based on the received commands. For simplicity, we’ll simulate robot control by printing the received velocities.

• Create the Python Script: Create a file named `robot_control_node.py` in the `my_teleop_pkg/my_teleop_pkg` directory.
• Implement the Node: Here’s a sample script:

  # my_teleop_pkg/my_teleop_pkg/robot_control_node.py
  import rclpy
  from rclpy.node import Node
  from my_teleop_pkg.msg import Teleop
  
  class RobotControlNode(Node):
      def __init__(self):
          super().__init__('robot_control_node')
          self.subscription = self.create_subscription(
              Teleop,
              'teleop_commands',
              self.listener_callback,
              10)
          self.subscription  # prevent unused variable warning
  
      def listener_callback(self, msg):
          self.get_logger().info('Received: Linear: %f, Angular: %f' % (msg.linear_velocity, msg.angular_velocity))
          # Here, you would implement the actual robot control logic
          # For example, send commands to motors based on msg.linear_velocity and msg.angular_velocity
  
  
  def main(args=None):
      rclpy.init(args=args)
      robot_control_node = RobotControlNode()
      rclpy.spin(robot_control_node)
      robot_control_node.destroy_node()
      rclpy.shutdown()
  
  if __name__ == '__main__':
      main()
  

• Make the Script Executable:

  chmod +x my_teleop_pkg/my_teleop_pkg/robot_control_node.py

• Update `setup.py`: Add the script to the entry points in `setup.py`:

  entry_points={
          'console_scripts': [
              'teleop_node = my_teleop_pkg.teleop_node:main',
              'robot_control_node = my_teleop_pkg.robot_control_node:main',
          ],
      },

• Rebuild the Package:

  colcon build

• Source the Workspace Again:

  source install/setup.bash

Testing the Teleoperation System ✅

Finally, let’s test our ROS 2 Teleoperation System. Launch the robot control node in one terminal and the teleoperation node in another. Use the keyboard to send commands and observe the output in the robot control node’s terminal.

• Launch Robot Control Node:

  ros2 run my_teleop_pkg robot_control_node

• Launch Teleoperation Node:

  ros2 run my_teleop_pkg teleop_node

• Control with Keyboard: In the teleoperation node’s terminal, use ‘w’, ‘a’, ‘s’, ‘d’ to control the robot (simulated in this case), and ‘q’ to quit.
• Observe Output: Observe the output in the robot control node’s terminal. It should print the received linear and angular velocities based on your keyboard inputs.

FAQ ❓

Q: What is ROS 2 and why should I use it for robotics?

ROS 2 (Robot Operating System 2) is a flexible framework for writing robot software. It provides tools and libraries for hardware abstraction, device drivers, communication between processes, and much more. Using ROS 2 simplifies the development of complex robotic systems by providing a standardized platform and a rich ecosystem of packages. ROS 2 is used by researchers and professionals alike to build everything from autonomous vehicles to industrial robots.

Q: What if I encounter errors during the installation or build process?

Errors during installation or building can be frustrating, but they are often easily resolved. Double-check that you have followed the instructions carefully, particularly regarding dependencies and environment setup. Consult the ROS 2 documentation and online forums for solutions to common errors. Ensure you source the ROS 2 workspace every time you open a new terminal and before running any ROS 2 commands.

Q: How can I extend this simple teleoperation system to control a real robot?

To control a real robot, you would replace the simulated robot control logic in the `robot_control_node.py` with code that interfaces with the robot’s hardware. This typically involves using robot-specific drivers and libraries to send commands to the robot’s motors or actuators. You would need to adapt the message types and control algorithms to match the specific requirements of your robot.

Conclusion

Congratulations! 🎉 You’ve successfully built a simple ROS 2 Teleoperation System. This tutorial provided a foundational understanding of ROS 2 concepts and practical experience in creating a remote control system. By defining custom message types, implementing Python nodes, and understanding the communication flow, you’ve taken a significant step towards mastering ROS 2 for robotics applications. This knowledge can be applied to more complex projects, like controlling robots in DoHost data centers for remote maintenance or creating immersive remote-controlled vehicles. Keep experimenting, and you’ll be amazed at what you can achieve! 📈

Tags

ROS 2, teleoperation, robotics, Python, robot control

Meta Description

Build a simple teleoperation system with ROS 2! Learn how to control robots remotely using Python, ROS 2 nodes, and custom message types.