10 things you need to know about ROS! | Getting Ready to Build Robots with ROS #4

Summary

In this video, the presenter offers a comprehensive overview of ROS2 (Robot Operating System), detailing its core components and practical usage, such as connecting and interacting with lidar devices. The tutorial covers essential ROS2 concepts like nodes, topics, services, parameters, and remapping, while highlighting key commands and features to manage nodes, communicate between devices, and structure projects. The video also addresses launching scripts, creating packages, and managing dependencies. A brief introduction to Quality of Service (QoS) in ROS2 is provided, helping viewers understand potential pitfalls when nodes don’t communicate due to incompatible settings. Ideal for beginners in robotics and ROS2.

Takeaways

• 😀 ROS (Robot Operating System) is not an operating system, but a collection of tools and libraries to help build complex robotic systems.
• 😀 ROS2 is the upgraded version of ROS1, with new features and improvements, and is the focus for this tutorial.
• 😀 A ROS system is made up of nodes, which are individual programs that communicate with each other to perform specific tasks.
• 😀 Nodes communicate using topics, where publishers send messages to subscribers. This allows nodes to remain simple and focused on their task.
• 😀 ROS nodes can run on a single machine or be distributed across multiple machines, offering flexibility in system design.
• 😀 ROS supports services, which allow a request/response communication method between nodes, useful for single-message exchanges.
• 😀 Parameters and remapping in ROS allow customization of node behavior and topic names, making it easier to handle complex systems with multiple components.
• 😀 ROS uses namespaces to organize nodes, helping avoid conflicts in topic names when working with multiple similar components, like multiple lidars.
• 😀 Launch files in ROS2 are written in Python (instead of XML as in ROS1) and help automate the launching of nodes with parameters and remapping.
• 😀 A ROS project is organized into packages, which contain nodes, launch files, and other related resources, and packages can have dependencies on other packages.
• 😀 ROS uses a build tool called `colcon` to compile workspaces, making it easier to manage packages and dependencies within a project.

Q & A

What is ROS and what does it stand for?

ROS stands for Robot Operating System, but it is not actually an operating system. It is a set of common libraries and tools that help build complex robotic systems.

What is the difference between ROS1 and ROS2?

ROS2 is the upgraded version of ROS1, and it was developed with significant improvements. While ROS1 is no longer receiving updates, ROS2 focuses on modern features and supports newer versions of Ubuntu and other platforms.

How are nodes used in ROS?

In ROS, nodes are individual programs that perform specific tasks, such as reading data from sensors, controlling motors, or sending operator commands. Nodes communicate with each other to form a complete robotic system.

What is the role of topics in ROS?

In ROS, topics are named channels where nodes can publish messages (as publishers) and other nodes can subscribe to receive those messages. Topics allow for flexible communication between nodes within the ROS ecosystem.

What are ROS services and how do they differ from topics?

Services in ROS enable request-response communication between nodes, providing a way for one node to send a request and receive a response. This is different from topics, where messages are broadcast to multiple subscribers.

What are ROS parameters and how are they used?

ROS parameters allow users to configure specific behaviors of nodes, such as setting the serial port for a lidar. Parameters can be passed to nodes at runtime to modify their operation.

What is remapping in ROS?

Remapping in ROS allows you to change the names of topics, services, or parameters at runtime. This is useful when you have multiple nodes that need to communicate but expect different names for topics.

What is the purpose of ROS launch files?

ROS launch files automate the launching of multiple nodes with specific parameters, remappings, and namespaces. In ROS2, launch files are typically written in Python and can be used to run nodes in a predefined configuration.

How does ROS handle package organization?

ROS organizes related files into packages, which group nodes, launch files, models, and dependencies together. A package may depend on other packages to fulfill its functionality.

What is the role of colcon in ROS?

Colcon is the build tool in ROS2 that compiles and installs packages. It handles dependencies, builds source files, and creates necessary directories, ensuring that ROS packages are properly set up for use.