Introduction to ros2 installation and basic knowledge

ros Introduce

ROS（Robot Operating System） Is an open source robot operating system ,ROS The system is composed of a large number of nodes , Any of these nodes can be published / Subscribe to communicate with other nodes . Take a chestnut , The radar unit in a position sensor on the robot can be used as ROS A node of , It can release the information obtained by radar in the form of information flow , The published information can be used by other nodes such as navigation units 、 Path planning unit, etc , The navigation and path planning unit itself is also a node , Similarly, the information obtained by each party is released in the form of information flow , For other nodes

ros2 install

This time it's in Ubuntu 22.04 Installation on system ros2 Of humble edition

1. Set the coding format of the terminal

   sudo apt update && sudo apt install locales -y
   sudo locale-gen en_US en_US.UTF-8
   sudo update-locale LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8
   export LANG=en_US.UTF-8
   

2. Enable Universe The repository

   sudo apt install software-properties-common
   sudo add-apt-repository universe
   

3. Add source

   First update the software and download and install curl、gnupg and lsb-release

   sudo apt update && sudo apt install curl gnupg lsb-release -y
   

   Get the key of the source and save it to the specified directory , Only locally GPG Key to download and install ros2 Software for

   sudo curl -sSL https://raw.githubusercontent.com/ros/rosdistro/master/ros.key -o /usr/share/keyrings/ros-archive-keyring.gpg
   

   An error is reported here Failed to connect to raw.githubusercontent.com port 443 after 17 ms: Connection refused, The solution is as follows ：

   1. visit This website see raw.githubusercontent.com The domain name corresponds to IP Address , see DNS Resource Records Information in

   2. Execute commands at the terminal sudo vi /etc/hosts, open hosts file

   3. Choose one , take IP And domain name added to hosts In file , Such as ：185.199.108.133 raw.githubusercontent.com

      If you execute the order again, you won't report a mistake

4. Add software source and update index

   echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/ros-archive-keyring.gpg] http://packages.ros.org/ros2/ubuntu $(source /etc/os-release && echo $UBUNTU_CODENAME) main" | sudo tee /etc/apt/sources.list.d/ros2.list > /dev/null
   

5. install ros2 package

   Update the system software first

   sudo apt update && sudo apt upgrade -y
   

   install ros2, The version is humble The desktop version , This installation takes a long time , Please be patient , If there is an error, it is basically a network problem , Please check by yourself

   sudo apt install ros-humble-desktop -y
   

6. Set up the environment

   The purpose is to let the operating system know ros2 Where is it installed , Use source Order or . command , Load environment information

   source /opt/ros/humble/setup.bash or . /opt/ros/humble/setup.bash

   This command can only take effect on the current terminal , Reopening the terminal requires another execution , You can add this command to .bashrc There is no need to execute every time in the file , The system can recognize ros2 command

   echo "source /opt/ros/humble/setup.bash" >> ~/.bashrc
   

7. verification ros2 installation is complete

   ros2 Provides C++ and python Of demo, Execute the following command at the terminal , As publisher

   ros2 run demo_nodes_cpp talker
   

   Open another terminal , As a listener, execute the following commands

   ros2 run demo_nodes_py listener
   

   listener Can see talker Constant news , explain ros2 Installation successful

ros2 Core concept of

• working space （Workspace）： Project location

• Function pack （Package）： The storage place of each function module developed

• node （Node）： Working cells of robots , Used to create publishers 、 subscriber 、 Service etc.

• topic of conversation （Topic）： A bridge for transferring data between nodes

• service （Service）： Between nodes, you ask me and answer , It consists of a pair of messages ( Request and reply )

• communication interface （Interface）： Standard structure of data transmission

• Parameters （Parameter）： Global dictionary of robot system

• action （Action）： Process management of complete behavior

• Distributed communication （Distributed Communication）： Task allocation of multiple computing platforms

• DDS（Data Distribution Service）： Neural network of robot

turtlesim and rqt Installation and use

• turtlesim and rqt Introduce

  Turtlesim It's for learning ros2 Lightweight simulator for , It shows ros2 Work done at the basic level , In order to understand what can be done with real robots or robot simulations in the future

  rqt yes ros2 Graphical interface of (GUI) Tools , What can be done on the command line rqt Can also do ,rpt Provides a more concise 、 In a more friendly way ros2 The elements of

• turtlesim and rqt install

  Perform the following installation turtlesim and rqt

  sudo apt update
  sudo apt install ros-humble-turtlesim ~nros-humble-rqt* -y
  

• start-up turrlesim

  Executing the following command will bring up the simulator window , Randomly display a small turtle

  ros2 run turtlesim turtlesim_node
  

• Use turrlesim

  Do not turn off the last terminal , Open a new terminal , Carry out orders

  ros2 run turtlesim turtle_teleop_key
  

  then , Click the direction key on the keyboard on this terminal to make the little turtle move

  

  Do not close the above two terminals , Open a new terminal again , Now open 3 Terminals , Execute the following commands on the new terminal to view the currently used nodes 、 topic of conversation 、 Services and actions

  ros2 node list		#  View the list of nodes 
  ros2 topic list		#  Check the list of topics 
  ros2 service list	#  View the list of services 
  ros2 action list	#  View the action list 
  

• start-up rqt

  The input terminal rqt, You can open rqt window

• adopt rqt Post topic news

  Select... In the menu bar Plugins → Topics → Message Publisher, call /turtle1/cmd_vel In service geometry_msgs/msg/Twist type , Modify linear velocity and angular velocity , Then post the topic , The little turtle will move its position according to the set value , As shown in the figure below

  

• Issue topic messages by command

  Let the little turtle move using command line operation , The order is as follows ,rate Parameters can be understood as 1 Once per second , The default is 1 second , You can add parameters --once Only once , Otherwise, the command will be executed all the time , Keep drawing circles

  ros2 topic pub -r 1 /turtle1/cmd_vel geometry_msgs/msg/Twist "{linear:{x: 3.0,y: 0.0,z: 0.0},angular:{x: 0.0,y: 0.0,z: 2.2}}"
  

  

• adopt rqt call /spawn Service creation Little Turtle

  Select... In the menu bar Plugins → Services → Service Caller, call /spawn The service can create a new little turtle , Set the position where the little turtle appears 、 Angle and name , Click on 【Call】 stay turtlesim The window will show a new little turtle , As shown in the figure below

  

• Call... By command /spawn Service creation Little Turtle

  You can also use commands to operate , The order is as follows

  ros2 service call /spawn turtlesim/srv/Spawn "{x: 3,y: 2,theta: 0.5,name: "test"}"
  

  Turtle name can be empty , The default name of a little turtle is turtle1, If it is empty , The new name of the little turtle is turtle2……

Clone sample project

1. Create workspace

   mkdir -p ~/dev_ws/src && cd ~/dev_ws/src #  Create and enter the workspace 
   

2. Clone the little turtle project into the work area

   sudo apt install git -y
   sudo git clone https://github.com/ros/ros_tutorials.git -b humble
   

3. Resolve dependencies

   cd .. #  Don't stop at src Under the table of contents , Go back to dev_ws Catalog 
   sudo apt install python3-rosdep2 -y	#  install python3-rosdep2
   rosdep update	#  initialization rosdep
   

   Encounter newspaper ERROR: unable to process source [https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml], It's still caused by the network , The solution is as follows ：

   1. Connect phone hotspot

   2. Execute commands at the terminal

      sudo vim /etc/ros/rosdep/sources.list.d/20-default.list
      

   3. In the original url with https://ghproxy.com/, As shown below

      yaml https://ghproxy.com/https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/osx-homebrew.yaml osx
      yaml https://ghproxy.com/https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/base.yaml
      yaml https://ghproxy.com/https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/python.yaml
      yaml https://ghproxy.com/https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/ruby.yaml
      gbpdistro https://ghproxy.com/https://raw.githubusercontent.com/ros/rosdistro/master/releases/fuerte.yaml fuerte
      

   4. Then execute the following command to complete the initialization ！ If it's still wrong , Please try other online methods by yourself

      sudo apt-get update
      rosdep update
      

      

   Finally, execute the command to solve the dependency

   rosdep install -i --from-path src --rosdistro humble -y
   

   appear All required rosdeps installed successfully It means completion

colcon structure

colcon Is a universal build tool ,ros Although the system is not recommended, the official documents still use this tool , Let's also demonstrate this , For more information about building tools, please check This article

install colcon

sudo apt install python3-colcon-common-extensions

Execute the following command to build all packages in the workspace

colcon build

Because automatic loading has been configured above ros2 Environmental information , Now we need to run this project , It is necessary to load the environment required by this project on this basis , After building , Open a new terminal , Execute the following command

source ~/dev_ws/install/local_setup.sh

At this time, execute the following command , What started is the local little turtle

ros2 run turtlesim turtlesim_node

It can be modified by setWindowTitle("TurtleSim") Verify the window name in and execute the following command , Amendment No 52 Window name of the row

vim ~/dev_ws/src/ros_tutorials/turtlesim/src/turtle_frame.cpp

Then rebuild the package

colcon build 

Execute the following command again to see that the window name has been modified

ros2 run turtlesim turtlesim_node

ros2 Common commands

About operation commands, you should use more tab Key automatic completion function and -h View help documents , The following commands are not introduced about optional parameters , Check more help documents ！

If there is no automatic completion function , It's the lack of python3-argcomplete The installation package causes , Restart the terminal after executing the following commands

sudo apt-get install python3-argcomplete

meaning	command
Create Feature Pack	ros2 pkg create --build-type ament_python <package_name>
View the function pack list	ros2 pkg list
View the list of executable files in the package	ros2 pkg executables <package_name>
Run the executable file in the package	ros2 run <package_name> <executable_name>
View the list of currently active nodes	ros2 node list
View node details	ros2 node info <node_name>
List the currently available topics	ros2 topic list
Check the message type of the topic	ros2 topic type <topic_name>
List the currently available topics and types	ros2 topic list -t
Check the topic message type 、 Number of publishers and subscribers	ros2 topic info <topic_name>
Find relevant topics according to the message type	ros2 topic find <message_type>
according to header The timestamp in calculates the message delay	ros2 topic delay <topic_name>
Display the average publishing frequency of current topics in real time	ros2 topic hz <topic_name>
Show the bandwidth of the current topic in real time	ros2 topic bw <topic_name>
Display topic messages in real time on the console	ros2 topic echo <topic_name>
Issue topic messages by command	ros2 topic pub <topic_name> <message_type> <message_content>
See all the services	ros2 service list
View service types	ros2 service type <service_name>
Output all services and types	ros2 service list -t
List all services of the specified type	ros2 service find <service_type>
Call the service	ros2 service call <service_name> <service_type>
View all actions	ros2 action list
View action information	ros2 action info <action_name>
View all actions and types	ros2 action list -t
Launch action target	ros2 action send_goal <action_name> <action_type> <goal>
View information about available plug-ins	ros2 bag list <plugin_type>
Record the data of the specified topic	ros2 bag record <topic_name>
Record data of multiple topics and customize file names	ros2 bag record -o <bag_file> <topic_name> <topic_name>……
View record information	ros2 bag info <bag_file>
Playback recorded information	ros2 bag play <bag_file>
View all parameters	ros2 param list
View the value of the specified parameter	ros2 param get <node_name> <parameter_name>
Set the value of the specified parameter	ros2 param set <node_name> <parameter_name> <value>
See parameter details	ros2 param describe <node_name> <parameter_name>
Transfer node parameters to yaml In file	ros2 param dump <node_name> --output-dir <dir_name>
Load the parameter file of the node	ros2 param load <node_name> < parameter_file>
Delete parameters	ros2 param delete <node_name> <parameter_name>
Classification shows all interfaces	ros2 interface list
View the list of packages that provide interfaces	ros2 interface packages
Check the interface in the package	ros2 interface package <package_name>
View the details of the specified interface	ros2 interface show <interface_name>
View the specified interface prototype	ros2 interface proto <interface_name>
adopt launch Files run multiple nodes at once	ros2 launch <package_name> <launch_arguments>

For more functions and operations, please check Official documents Well ！