Simple Turtlebot Simulation in ROS | ROS 101 | ROS Tutorials for Beginners | Lesson 3

Summary

This video script offers an introduction to ROS (Robot Operating System) through the TurtleSim package, teaching viewers how to navigate and control a simulated robot. It covers ROS utilities, node architecture, and basic kinematics. The tutorial dives into creating a 'turtle play' package, publishing velocity commands, and subscribing to pose feedback. It also explains the difference between global and local coordinates and the importance of feedback in robot control, providing a foundational understanding of mobile robot simulation in ROS.

Takeaways

• 😀 The course introduces ROS (Robot Operating System) utilities like publishers and subscribers and discusses the architecture of nodes working on individual tasks while maintaining communication.
• 🌐 The importance of using the terminal for navigating ROS instead of just relying on the GUI is emphasized.
• 🐍 The session includes a first mobile robot simulation using TurtleSim, a ROS package for simulating a turtle-like robot.
• 📚 A brief introduction to robot kinematics is provided, focusing on motion-related variables without considering forces, masses, and inertias.
• 🔍 The instructor demonstrates how to investigate ROS topics and messages, showing how to use commands like `rostopic list` and `rostopic info`.
• 📈 The script explains the data type 'geometry_msgs/Twist', which is used for representing velocity in ROS, composed of linear and angular velocity vectors.
• 📝 The process of creating a ROS package called 'turtle_play' is outlined, including setting up a script to control the turtle's movement.
• 🤖 The concept of publishers and subscribers in ROS is clarified, with the turtle simulation needing a publisher to send velocity commands for movement.
• 🔄 The script covers the creation of a subscriber to receive pose feedback from the turtle, highlighting the importance of feedback in robot control.
• 📚 The difference between global and local coordinates in robot kinematics is discussed, explaining how velocity is a local quantity relative to the robot's body frame.

Q & A

What is the main focus of the 'ros101 fun approach' course?

The main focus of the 'ros101 fun approach' course is to teach students how to use ROS (Robot Operating System) utilities such as publishers and subscribers, and to understand the architecture where multiple nodes work on individual tasks while maintaining communication to achieve project goals.

Why is the ROS wiki considered an important resource when dealing with ROS?

The ROS wiki is considered an important resource because it provides detailed instructions and documentation on how to start simulations, understand ROS packages, and navigate through various ROS functionalities, which is crucial for ROS developers.

What is the purpose of the 'turtlesim' package in ROS?

The 'turtlesim' package in ROS is used for simulation purposes. It provides a simple 2D environment where a 'turtle' can be controlled and manipulated to understand basic robot motion and ROS topics without the need for a physical robot.

How does the speaker plan to make the turtle in the 'turtlesim' package move?

The speaker plans to make the turtle move by creating a publisher in a new ROS package called 'turtle_play'. This publisher will publish velocity values to the 'cmd_vel' topic, which the turtle simulation is subscribed to, thus making the turtle move.

What is the significance of the 'geometry_msgs/Twist' message type in the context of the 'turtlesim' package?

The 'geometry_msgs/Twist' message type is significant because it represents a composite message made up of two vectors denoting linear and angular velocity. This message type is used to control the movement of the turtle in the 'turtlesim' package by publishing velocity commands.

What is the difference between a ROS topic and a ROS message?

A ROS topic is a type of inter-process communication mechanism that allows nodes to publish and subscribe to messages. A ROS message, on the other hand, is the data structure being passed along these topics, containing specific information such as velocity or pose data.

Why is the 'rostopic info' command used in the script?

The 'rostopic info' command is used to investigate the properties of a ROS topic, such as its type, the publishers and subscribers it has, and the message structure, which helps in understanding and debugging ROS applications.

What is the role of the 'catkin_create_pkg' command in the script?

The 'catkin_create_pkg' command is used to create a new ROS package within a catkin workspace. In the script, it is used to create the 'turtle_play' package where the code for controlling the turtle will be placed.

How does the speaker use a for loop in the Python script to control the turtle's movement?

The speaker uses a for loop to repeatedly publish velocity messages for a certain number of iterations, effectively controlling the duration of the turtle's movement in the 'turtlesim' package.

What is the purpose of the 'rospy.spin()' call in the subscriber part of the script?

The 'rospy.spin()' call is used to keep the subscriber node running and responsive to incoming messages. It allows the callback function to be executed whenever a new message is received on the subscribed topic.

How does the pose of the turtle in 'turtlesim' relate to its kinematics?

The pose of the turtle, which includes its x and y coordinates and its orientation (theta), represents its position and orientation in the 2D space. This is a fundamental aspect of kinematics, which deals with the motion of robots without considering the forces that cause the motion.