Basic robot software ROS basics and programming practice course

Introduction to ROS

The world of robotics has grown significantly over the years, with technology becoming more sophisticated and accessible.
Robotic Operating System, commonly known as ROS, is one of the essential tools in the field of robotics.
ROS is an open-source framework designed to develop software for robots.
Whether you are a beginner or an experienced developer, understanding the basics of ROS is crucial.

ROS is not a traditional operating system like Windows or Linux.
Instead, it is a flexible framework for writing robot software.
It provides various tools, libraries, and conventions that aim to simplify the process of developing complex and robust robot applications.

Why Use ROS?

ROS has developers’ support from around the globe, making it a widely-used standard in the robotics industry.
One of its greatest advantages is its ability to work with various types of robots, sensors, and actuators.
Additionally, it simplifies the integration of hardware and software components due to its versatile communication infrastructure.

Since ROS is open-source, it allows for an active community that constantly contributes to improvements and updates.
This community support is invaluable as it provides numerous libraries and codes to help start new projects or improve existing ones.
Moreover, ROS can work on different types of hardware, ranging from a small microcontroller to a powerful processing unit.

Understanding the ROS Structure

To use ROS effectively, you need to familiarize yourself with its structure.
The main components of a ROS system include nodes, topics, services, messages, and packages.

Nodes

Nodes are the fundamental building blocks in ROS.
A node is an executable that uses ROS to communicate with other nodes.
As a developer, you can write a simple node for joint movement controls, or a complex one for image processing.
Nodes communicate with each other using topics, services, or actions, and can be programmed in multiple languages, such as Python or C++.

Topics

In ROS, nodes exchange information using topics.
A topic is a named bus over which nodes can exchange messages.
There are publishers for sending messages and subscribers for receiving them.
This publish/subscribe model is highly flexible and allows for asynchronous communication between nodes.

Messages

Messages are data structures used to communicate over topics.
A message can contain various fields, such as integers, floating-point numbers, or even other message types.
ROS provides several standard message types, but you can also define your custom messages for specific needs.

Services

While topics are great for continuous data flow, sometimes nodes need to communicate through a request/reply model.
This is where services come in.
A service allows a node to send a request to another node and receive a reply in return.
Services are ideal for operations that wait until completion, such as retrieving sensor data or initiating an action.

Packages

A package is a collection of nodes, code, and other resources that are organized together.
It is the fundamental unit of software organization in ROS.
Each package should have a defined purpose, such as controlling a specific sensor or processing a particular type of data.
Packages make it easy to share and reuse code within and across projects.

Getting Started with Programming in ROS

Creating a successful robotic application requires a good understanding of programming in ROS.
Here’s a step-by-step guide to help you get started.

Installing ROS

Before writing your first program, you need to install ROS on your computer.
This usually involves adding the ROS repository to your system and installing basic ROS packages using a package manager.
Detailed installation guides are available for various versions of ROS, such as ROS Noetic or ROS 2.

Creating a Workspace

A workspace in ROS is a directory where you can organize and build your own ROS packages.
To create a workspace, follow the steps:

1. Open a terminal window.
2. Create a directory for your workspace.
3. Inside this directory, create another directory named `src` for your source code.
4. Run the `catkin_make` command to initialize your workspace.
5. Finally, source your workspace using the `source devel/setup.bash` command to make ROS aware of it.

Writing a Simple Node

Once your workspace is set up, you can start writing nodes.
Here’s a basic example in Python:

1. Create a package using the command `catkin_create_pkg` followed by your package name and dependencies.
2. Navigate to your package’s `src` directory.
3. Create a new node file and open it for editing.
4. Write a simple Python script that, for example, prints “Hello, ROS!” to the console.

Here is a sample code snippet:

“`python
#!/usr/bin/env python

import rospy

def hello_ros():
rospy.init_node(‘hello_ros_node’)
rospy.loginfo(“Hello, ROS!”)

if __name__ == ‘__main__’:
try:
hello_ros()
except rospy.ROSInterruptException:
pass
“`

5. Make your node executable with the `chmod +x` command.
6. Launch your node using the `rosrun` command with your package and node name.

Conclusion

The Robotics Operating System provides a solid foundation for robotics software development.
By understanding its components and familiarizing yourself with its programming practices, you can enhance your ability to create diverse and functional robotic applications.
Whether you’re aspiring to enter the field of robotics or expand your current skills, learning ROS offers countless opportunities for innovation and creativity.