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Intro to ROS

Modified 5 days ago by Dev Ramesh

Student version

Hardware - Basestation

Previous Lesson - Sensing

Knowledge -

  • Definition and purpose of robot middleware

  • Basic ROS components and vocabulary: topic, message, publisher, subscriber, node, workspace

Skills -

  • List and echo ROS topics

  • Create a catkin workspace

Introduction to ROS

Modified 2020-07-21 by Peyton Strong

STANDARDS: Next Generation Science Standards (NGSS) and International Society for Technology in Education (ISTE)

Modified 2020-07-23 by Dev Ramesh

NGSS: HS - ETS1 - 2: Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

ISTE: 1. d.: Understand the fundamental concepts of technology operations, demonstrate the ability to choose, use and troubleshoot current technologies and are able to transfer their knowledge to explore emerging technologies.

Assessments and Evidence of Understanding

Modified 2020-07-23 by Peyton Strong

Students will be able to undertand what ROS is and make a catkin workspace by the end of the lesson.

AGENDA (Brief Summary of Activities)

Modified 2020-07-23 by Peyton Strong

5 mins: Introducing ROS

45 mins: Reviewing important ROS concepts and commands

10 mins: Making a catkin workspace

Differentiation (strategies for grouping, ELL, and inclusion)

Modified 2020-04-16 by Garrett Warren

Advanced preparation/Materials/Set Up (Including Misconceptions)

Modified 2020-08-12 by unknown

Teacher Materials

Basestation, a projector (if needed)

Classroom Set Up

Teachers can write a DO NOW on the board for students to set up their basestations.

SCRIPT OF TEACHING AND LEARNING ACTIVITIES

Modified 2020-04-16 by Garrett Warren

Introducing The Lesson

Modified 2020-08-12 by unknown

Hook

Teachers use this link to:

  1. Give students a sense of the structure of a software diagram.

  2. Illustrate the challenges of software engineering in robotics

    • Lots of sensors and actuators, and they need to communicate with each other (even in this diagram, not many sensors and actuators but the connections are still fairly complicated)

    • Processes might live on different computers to spread the computing load

    • Many software modules need to work together (Need to manage their dependencies)

Main Lesson

Modified 2020-08-12 by unknown

Present our solution to the challenges above: ROS (Robot Operating System).

Official Introduction of ROS

“ROS is an open-source, meta-operating system for your robot. It provides the services you would expect from an operating system, including hardware abstraction, low-level device control, implementation of commonly-used functionality, message-passing between processes, and package management. It also provides tools and libraries for obtaining, building, writing, and running code across multiple computers.” (http://wiki.ros.org/ROS/Introduction)

In Short: ROS aims to support code reuse in robotics research and development.

What are the benefits of reusing codes?

- **Wikipedia Verision** "Modular programming is a software design technique that emphasizes separating the functionality of a program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of the desired functionality." (https://en.wikipedia.org/wiki/Modular_programming)

- **In Short**: Easy to read, easy to test, easy to reuse, easy to maintain, etc.

To help students understand this, teachers might draw a comparison to reading and writing a book like [this](https://www.durhampriory.ac.uk/colour-your-own-medieval-manuscript-part-5/) versus a book like [this](https://docs.duckietown.org/daffy/downloads/duckiesky_high_school/docs-duckiesky_high_school/branch/daffy-develop/doc-duckiesky_high_school/out/index.html)

Overview of important ROS concepts

ROS master: A node that every other node register in order to communicate with each other. It is created by running roscore command (Detailed: http://wiki.ros.org/Master)

ROS nodes: ROS nodes are programs that communicate with other programs via publishing and/or subscribing to ROS topics. (Detailed: http://wiki.ros.org/Nodes)

Messages: The information that is communicated between nodes. Messages are standardized, which means that certain message types have certain fields. For example, “ROS pose message” has two parameters: position and orientation. They are message types themselves, which contain their own parameters. (http://docs.ros.org/melodic/api/geometry_msgs/html/msg/Pose.html) This makes communication between programs a lot easier (link to the modular programming above). You can even create your own message types!

ROS Topics: Topics are what ROS messages are published and subscribed to. (Detailed: http://wiki.ros.org/Topics)

Publishers: Publishers are used to publish specific message types to specific topics.

Subscribers: Subscribers are used to read the messages being published to a ROS topic.

Print out all of the topics running by entering “rostopic list” into a free window after running ‘screen -c pi.screenrc’ on your drone. Have messages that are being published to a topic printed out by navigating to an empty window in the screen and entering “rostopic echo [topic_name]”. For example, if you wanted to see the data coming from the infrared sensor, you could enter “rostopic echo /pidrone/infrared”

Important ROS Commands:

roslaunch: roslaunch is a tool for easily launching multiple ROS nodes locally and remotely via SSH, as well as setting parameters on the Parameter Server. (Detailed: http://wiki.ros.org/roslaunch)

roscd: roscd allows you to change directories using a package name, stack name, or special location. (Detailed: http://wiki.ros.org/rosbash#roscd)

rostopic: rostopic contains the rostopic command-line tool for displaying debug information about ROS Topics, including publishers, subscribers, publishing rate, and ROS Messages. (Detailed: http://wiki.ros.org/rostopic)

In your future lesson about ROS subscriber, you will create a ROS program to control your LED according to readings in of your sensor. In this case, there will be three nodes: sensor, LED, and controller. The controller node subscribes to the sensor node, receiving its value, determines how the LED should behave, and then publishes its message to the LED node.

Ending The Lesson

Modified 2020-08-12 by unknown

make a catkin workspace following this link.

Useful Resources and References

ROS overview

ROS Wiki