[ros2] Why use ros2? Introduction to ros2 system characteristics

One 、 Why launch ROS2？

2010 year ,ROS1 First release of official version , The original intention of its research and development is to design PR2（ Personal service robot ） Common software architecture . But as the ROS1 Popularization of technology ,ROS1 Began to be widely integrated into the research and development of unmanned systems in various fields , Many problems of the system have been exposed . In order to meet the needs of robot research and development in the new era ,2022 year 5 month ,ROS The developer team launched a new version ROS2.

（ One ）ROS1 The birth of

2007 year , Stanford students are developing PR2（ Personal service robot ） Common software architecture , Design ROS The prototype of the .2010 year ,Willow Garage The company to launch ROS1 First release of .

（ Two ）ROS1 The problem is

ROS1 The earliest design goal ： For home service robots PR2, Design a software architecture for common development .

（1）PR2 characteristic

• Large size , Enough calculating power ： It is equipped with a workstation level computing platform and various advanced communication equipment , Don't worry about not being able to calculate , It has enough strength to support various complex real-time operations and processing ;
• Reliable communication ： Because it is a single soldier operation , The vast majority of communications are done internally , Then you can use a wired connection , Ensure a good network connection , There is no risk of losing data or hacking ;
• Laboratory products , No engineering applications ： The robot was eventually produced in small quantities , But because of the high cost and price , It can only be used for academic research .
  

（2）ROS1 Existing problems

With ROS1 Popularization of technology ,ROS1 Integrate into the research and development of unmanned systems in various fields . Originally only for PR2 Designed software architecture , There are many problems ：

• There is a great demand for resources ： Need to run in an embedded system with limited resources ;
• The anti-interference of the system is poor ： Ensure the reliability of communication in places with interference ;
• Poor product application ： We should make products and go to the market , Even used in autonomous vehicle and space robots .

（ 3、 ... and ）ROS2 Design thinking

（1）ROS2 Aimed at the scene

• Multi robot system ：ROS2 It provides a standard method and communication mechanism for the application of multi robot systems .
• Cross platform ： Robot application scenarios are different , The control platforms used will also vary greatly , In order for all robots to work ROS2,ROS2 It can run across platforms Linux、Windows、MacOS、RTOS, Even a microcontroller without any system （MCU） On .
• The real time ： Robot motion control and many behavior strategies require that robots have real-time performance , For example, robots should be reliable in 100ms Find pedestrians in front , Or stable in 1ms Complete the kinematics in the cycle 、 Solution of dynamics ,ROS2 It provides basic guarantee for such real-time requirements .
• network connections ： No matter what kind of network environment ,ROS2 Can try to ensure the integrity and security of a large number of robot data , For example wifi When the signal is bad, try your best to send the data , When there is a risk of hacker intrusion, the data should be encrypted and decrypted .
• Commercialization ： A large number of robots have come into our life , There will be more and more in the future ,ROS2 It can not only be used in the robot development stage , It can also be directly carried in the product , Go to the consumer market , This is right ROS2 The stability of 、 Strength also poses great challenges .
• project management ： Robot development is a complex system engineering , Design 、 Development 、 debugging 、 test 、 Deploy the whole process of project management tools and mechanisms , Will also be in ROS2 In the embodiment , It is more convenient for us to develop a robot .

（2） Design thinking

ROS The development team takes a long-term view , Select override ROS1 The software architecture of , Design a brand new ROS2 operating system . For the system architecture 、 Software code 、 The system compilation has been comprehensively upgraded .

• System architecture ： With the help of DDS Communication architecture , Realize system distribution
• software interface ：ROS2 combination C++ and Python3 The latest standard of , The redesign API Interface
• System compilation ： For big projects and python engineering , More friendly .
  

Two 、ROS2 System features

（ One ） System architecture

• Process management ： stay ROS1 in , You need to start the central node manager Master, Unified management of all nodes . If Master Node failure , Will seriously affect ROS system function . stay ROS2 in , The system introduces the node self discovery mechanism , It can effectively improve the robustness of the system .
• In-process communication ： Process internal communication ,ROS1 and ROS2 Shared memory is adopted .
• Interprocess communication ： stay ROS1 in , The communication between processes mainly depends on the underlying TCP\UDP agreement , But in ROS2 in , Introduce complex DDS System .

（ Two ） Communication architecture

ROS1 Is based on TCP/UDP communication system , With high latency 、 Losing data 、 Unable to encrypt . and ROS2 Use... At the communication level DDS Communication protocol .
DDS It is a communication protocol in the Internet of things , With multiple versions ,DDS It's an international standard , The software system that can implement this standard is not the only one . It can be provided by multiple manufacturers DDS System , such as OpenSplice、FastRTPS etc. , The performance of each company is different , The applicable scenarios are also different .
The software interfaces of each manufacturer are different , To solve this problem ,ROS2 Designed a ROS Middleware, abbreviation RMW, That is, specify a standard interface . For example, how to send data , How to receive data , How to configure various attributes of data , It's all defined , If the manufacturer wants to access ROS Community , You have to write an adaptive interface according to this standard , Put your own DDS Transplant it , In this way, the problem is handed over to the most familiar family DDS The manufacturer of . For us users , One of them DDS It doesn't work , Just install another , Then make a simple configuration , There is no need to change a single line of the program , Easily replace the underlying communication system .
For developers , In the product development stage , You can use open source DDS Meet the basic needs of the product , In the deployment and delivery phase , It can be changed to a more stable one DDS edition , To reduce development costs .
（ 3、 ... and ） The core concept
in order to ROS Continuity of developer development ,ROS2 Retain the ROS1 Basic concepts of .

ROS2 System learning , May refer to ： Ancient Moon House ROS2 introduction 21 speak