A lecture about how ROS works and the key differences between ROS1 and ROS2.

1. ROS: An open source platform for
robotics software developers
Amine BENDAHMANE
02 April 2021

2. Summary
2
1. What is ROS?
2. How ROS works?
3. Why to use ROS?
4. ROS2
5. Requirements to use ROS
6. Examples (moving a robot using ROS & python)

3. Context: Why I’m talking about this?
3
I pursued a multi-disciplinary career:
• Computer Science degree from USTO-MB
university
• Worked as Web Developer
• Studied Electronics for ~2 years (actually 1.5 years!)
• Pursuing a PhD degree in Artificial Intelligence & Robotics
• Teaching programming, robotics, and AI for several years

4. Context: What does robotics software do?
4
Collect data from sensors
Extract information
Send orders to actuators
Sense-Think-Act paradigm

5. 1. What is ROS?
5
ROS is not:
Robot Operating System

6. 1. What is ROS?
6
ROS is not:
• An operating system
Robot Operating System

7. 1. What is ROS?
7
ROS is not:
• An operating system
• A library
Robot Operating System

8. 1. What is ROS?
8
ROS is not:
• An operating system
• A library
• A simulator Robot Operating System

9. 1. What is ROS?
9
ROS is not:
• An operating system
• A library
• A simulator
• An AI framework
Robot Operating System

10. 1. What is ROS?
10
ROS is:
• A middleware
Operating System (OS)
Robot Hardware
ROS Ecosystem
User Software

11. 1. What is ROS?
11
ROS is:
• A middleware
• A distributed platform

12. 1. What is ROS?
12
ROS is:
• A middleware
• A distributed platform
• A set of libraires and tools
Visualization
Simulation
Messaging
Debugging
Packaging
Logging
Navigation, Mapping, Path
Planning…

13. 1. What is ROS?
13
ROS is:
• A middleware
• A distributed platform
• A set of libraires and tools
• Open Source (BSD license)

14. 2. How ROS works?

15. 15
Laser Node
Camera Node
Node
Node
Other nodes
Motors Node
Battery Node
2. How ROS works?

16. 16
Laser Topic
Laser Node
Camera Node
Publish
Node
Subscribe
Node
Other nodes
Motors Node
Battery Node
2. How ROS works?

17. 17
Laser Topic
Laser Node
Camera Node
Publish
Node
Subscribe
Node
Other nodes
Motors Node
Battery Node
2. How ROS works?
Service

18. 2. How ROS works?
18
Topics allow continuous asynchronous communication

19. 2. How ROS works?
19
Services allow one-time synchronous communication

20. 2. How ROS works?
20
The core concepts of ROS are:
• Nodes
• Topics
• Services
• Packages
• Messages
• Other (actions, parameters,
launch files, nodelets…)

21. 3. Why ROS?

22. 3. Why ROS?
22
ROS abstracts the Hardware (motors, sensors…)
• Example: When you want to move the motors, just send a
velocity message to the corresponding topic.
The same code works on
different robots

23. 3. Why ROS?
23
ROS takes care of network layer
• We don’t need to think about
RPC, TCP/UDP, Socket…

24. 24
Designed to increase reusability
• With a set of libraries for path planning, mapping,
visualization…
3. Why ROS?

25. 25
Language independent communication
• A node can run in python and another in C++, with smooth
communication
3. Why ROS?
Topic
Node 1 (C++)
Publisher
Subscriber
Node 2 (python)

26. 26
• Fast prototyping using simulators
• Easy transferring from simulated to real world
robots
3. Why ROS?

27. 27
• Handles transforms between coordinate frames
3. Why ROS?

28. 28
3. Why ROS?
• Visualization and debugging tools

29. 4. Why ROS 2?

30. 4. Why ROS 2?
30

31. 31
• Fully distributed (no ROS master)
• Allows real time programming
• Supports Linux, Windows, MacOS & RTOS
• Supports python >=3.5 & C++11/14 (C++17 soon)
• Allows multiple nodes in the same process
• Python & C++ APIs has the same base API
• …(more)
4. Why ROS 2?

32. 32
4. Why ROS 2?
ROS1 & ROS2 are evolving together:
• The last distribution of ROS1
(Noetic Ninjemys) will still be
supported until May 2025

33. 33
4. Why ROS 2?
Should I switch to ROS 2 now?
• 80% of ROS packages are based
on ROS 1 (as of January 2021)
https://metrics.ros.org/packages_rosdistro.html
• Stick to ROS 1 if you have legacy code or a large
ROS 1 code base already on production (do the
transition gradually)

34. 34
4. Why ROS 2?
• Most of the packages are based on distributions ≤ melodic
• It means most packages are based on C++03 or python 2.7

35. 35
You can use both versions at the same time:
• A node in ROS 1 can communicate with a node in ROS2
through ROS1_bridge package
• Requires more
CPU and RAM
4. Why ROS 2?

36. 5. Requirements to use ROS?

37. 5. Requirements to use ROS
37
You need to know:
• Basic Linux commands
• Basic programming in Python or C++
• Basic knowledge about robot hardware (what’s a
sensor, type of sensors, what’s an actuator…)
• More skills depending on what you want to do
(kinematics, geometry, objects-oriented programming…)

38. 6. Examples

39. 6. Examples
39
/cmd_vel
Our program
Publisher
Subscriber
Topic
Objective:
• create a ROS node to move the robot forward
Velocity commands:
(Moving forward => linear velocity)

40. 6. Examples
40
import rospy, time
from geometry_msgs.msg import Twist
rospy.init_node('robot_mover') # initialize ROS node
pub = rospy.Publisher('cmd_vel', Twist) # create a topic publisher to
control the motors
twist = Twist() # create a Twist message to send velocity commands
twist.linear.x = 0.2 # set linear velocity to 20% of max motor’s speed
moving_time = 0
t0 = time.time()
while moving_time < 3: # repeat the following actions for 3 seconds
pub.publish(twist) # publish to the topic (execute the velocity command)
moving_time = time.time() - t0
twist.linear.x = 0 # set linear velocity to 0 (to stop the motors)
pub.publish(twist) # publish the command

41. 6. Examples
41
Executing the same code on simulation and real robot:
Testing on P3DX at LARESI laboratory, USTO-MB
Testing on Turtlebot3 Gazebo simulation

42. 7. Conclusion

43. 7. Conclusion
43
• ROS is an open-source middleware for robotics
applications
• It is widely used in research & industry
• It abstracts the hardware and network layers
• It increases reusability, and allows easy transfer
from simulation to real robots
• ROS 1 & ROS 2 are evolving together until 2025

44. Thank you
AmineHorseman
https://github.com/amineHorseman/my-talks
https://linkedin.com/in/amine-bendahmane

45. Figures references
Page 11: https://www.slideshare.net/pibgeus/21-distributed-architecture-
deploymentinstrospection
Page 18: https://docs.ros.org/en/foxy/Tutorials/Topics/Understanding-ROS2-Topics.html
Page 19: https://docs.ros.org/en/foxy/Tutorials/Services/Understanding-ROS2-Services.html
Page 22: https://slideshare.net/takasehideki/ros-and-mros-how-to-accelerate-the-development-
of-robot-systems-and-integrate-embedded-devices
Page 23: “Message Encryption in Robot Operating System: Collateral Effects of Hardening Mobile
Robots”, Rodríguez Lera et al., Frontiers in ICT 5, 2018
Page 24: https://answers.ros.org/question/262417/amcl-not-localizing-in-pre-built-map
Page 26: (1) https://docs.fetchrobotics.com/gazebo.html (2) https://shuzhiduo.com/A/obzbYBW1dE
Page 27: (1) http://library.isr.ist.utl.pt/docs/roswiki/nao_description.html (2) “Singularity Avoidance
Control of a Non-Holonomic Mobile Manipulator for Intuitive Hand Guidance”, Weyrer et al.,
Robotics 8(1):14, 2019
Page 28: http://fontysarcr.blogspot.com/2016/06/progress-with-multi-robot-exploration.html
Page 30: “Exploring the performance of ROS2”, EMSOFT ‘16, Maruyama et al., 2016
Page 34: https://metrics.ros.org/packages_rosdistro.html
Page 35: https://github.com/m-yuya/ros1_evaluation/tree/master/evaluation