Robohub.org
 

ROS 101: Intro to the Robot Operating System

by
29 January 2014



share this:
ROS101_Clearpath

Clearpath Robotics brings us a new tutorial series on ROS!

Since we practically live in the Robot Operating System (ROS), we thought it was time to share some tips on how to get started with ROS. We’ll answer questions like where do I begin? How do I get started? What terminology should I brush up on? Keep an eye out for this ongoing ROS 101 blog series that will provide you with a top to bottom view of ROS that will focus on introducing basic concepts simply, cleanly and at a reasonable pace. This guide is meant as a groundwork for new users, which can then be used to jump into in-depth data at wiki.ros.org. If you are totally unfamiliar with ROS, Linux, or both, this is the place for you!

The ROS Cheat Sheet

This ROS Cheat Sheet is filled with tips and tricks to help you get started and to continue using once you’re a true ROS user. This version is written for ROS Hydro Medusa. Download the ROS Cheat Sheet here.

What is ROS?

ROS (Robot Operating System) is a BSD-licensed system for controlling robotic components from a PC. A ROS system is comprised of a number of independent nodes, each of which communicates with the other nodes using a publish/subscribe messaging model. For example, a particular sensor’s driver might be implemented as a node, which publishes sensor data in a stream of messages. These messages could be consumed by any number of other nodes, including filters, loggers, and also higher-level systems such as guidance, pathfinding, etc.

Why ROS?

Note that nodes in ROS do not have to be on the same system (multiple computers) or even of the same architecture! You could have a Arduino publishing messages, a laptop subscribing to them, and an Android phone driving motors. This makes ROS really flexible and adaptable to the needs of the user. ROS is also open source, maintained by many people.

General Concepts

Let’s look at the ROS system from a very high level view. No need to worry how any of the following works, we will cover that later.

ROS starts with the ROS Master. The Master allows all other ROS pieces of software (Nodes) to find and talk to each other. That way, we do not have to ever specifically state “Send this sensor data to that computer at 127.0.0.1. We can simply tell Node 1 to send messages to Node 2.

ros101-1
Figure 1

How do Nodes do this? By publishing and subscribing to Topics.

Let’s say we have a camera on our Robot. We want to be able to see the images from the camera, both on the Robot itself, and on another laptop.

In our example, we have a Camera Node that takes care of communication with the camera, a Image Processing Node on the robot that process image data, and a Image Display Node that displays images on a screen. To start with, all Nodes have registered with the Master. Think of the Master as a lookup table where all the nodes go to find where exactly to send messages.

ros101-2
Figure 2

In registering with the ROS Master, the Camera Node states that it will Publish a Topic called /image_data (for example). Both of the other Nodes register that they are Subscribed to the Topic /image_data.

Thus, once the Camera Node receives some data from the Camera, it sends the /image_data message directly to the other two nodes. (Through what is essentially TCP/IP)

ros101-3
Figure 3

Now you may be thinking, what if I want the Image Processing Node to request data from the Camera Node at a specific time? To do this, ROS implements Services.

A Node can register a specific service with the ROS Master, just as it registers its messages. In the below example, the Image Processing Node first requests /image_data, the Camera Node gathers data from the Camera, and then sends the reply.

ros101-4
Figure 4

We will have another tutorial “ROS 101 – Practical Example” next week.

 

See all the ROS101 tutorials here. If you liked this article, you may also be interested in:

See all the latest robotics news on Robohub, or sign up for our weekly newsletter.

 



tags: , , ,


Clearpath Robotics Clearpath Robotics is dedicated to automating the world's dullest, dirtiest and deadliest jobs through mobile robotic solutions.
Clearpath Robotics Clearpath Robotics is dedicated to automating the world's dullest, dirtiest and deadliest jobs through mobile robotic solutions.





Related posts :



Robot Talk Episode 90 – Robotically Augmented People

In this special live recording at the Victoria and Albert Museum, Claire chatted to Milia Helena Hasbani, Benjamin Metcalfe, and Dani Clode about robotic prosthetics and human augmentation.
21 June 2024, by

Robot Talk Episode 89 – Simone Schuerle

In the latest episode of the Robot Talk podcast, Claire chatted to Simone Schuerle from ETH Zürich all about microrobots, medicine and science.
14 June 2024, by

Robot Talk Episode 88 – Lord Ara Darzi

In the latest episode of the Robot Talk podcast, Claire chatted to Lord Ara Darzi from Imperial College London all about robotic surgery - past, present and future.
07 June 2024, by

Robot Talk Episode 87 – Isabelle Ormerod

In the latest episode of the Robot Talk podcast, Claire chatted to Isabelle Ormerod from the University of Bristol all about human-centred design and women in robotics.
31 May 2024, by

Robot Talk Episode 86 – Mario Di Castro

In the latest episode of the Robot Talk podcast, Claire chatted to Mario Di Castro from CERN all about robotic inspection and maintenance in hazardous environments.
24 May 2024, by

Congratulations to the #ICRA2024 best paper winners

The winners and finalists in the different categories have been announced.
20 May 2024, by





Robohub is supported by:




Would you like to learn how to tell impactful stories about your robot or AI system?


scicomm
training the next generation of science communicators in robotics & AI


©2024 - Association for the Understanding of Artificial Intelligence


 












©2021 - ROBOTS Association