Xayer / ros-bot

ROSBOT

My adventure of ROS starts here.

"Requirements"

Hardware

• Raspberry PI 4 8GB

Software

• Terminator
  • Shortcuts:
    • Ctrl + Shift + O - Split Window Horizontally
    • Ctrl + Shift + E - Split Window Vertically
• Ubuntu 20.04
• Python3
• ROS2
  • When trying to interact with ros, you need to setup your ~./bashrc with the following line. source /opt/ros/foxy/setup.bash this is to avoid resourcing all the time.
• python3-colcon-common-extensions - with autocomplete enabled;
  • cd /usr/share/colcon_argcomplete/hook and add source /usr/share/colcon_argcomplete/hook/colcon-argcomplete.bash to ~/.bashrc.
• make your ros workspace and source it.
  • make the workspace

  cd ~
  mkdir ros2_ws
  cd ros2_ws
  mkdir src
  colcon build
  

  • source ~/ros2_ws/install/setup.bash inside ~/.bashrc

Commands

• colcon build - to build all packages in the workspace.
• colcon build --packages-select <package> --symlink-install build only selected packages. --symlink-install will make a symlink to the package directly, instead of the compiled executeable.
• ros2 pkg create my_py_pkg --build-type ament_python --dependencies rclpy create new python ros package for
• ros2 pkg create my_cpp_pkg --build-type ament_cmake --dependencies rclcpp create new C++ ros package
• Start node ros2 run my_py_pkg py_node
• in case you want to run a file from the install directory, make sure you have permissions to run it, but running chmod +x NODE_NAME_HERE
• Start ROS2-Web-Bridge cd ~/ros2_ws/ros2-web-bridge && npm run wsserver.
• ros2 node list - list a curently running nodes
• ros2 node info <node> - list information regarding the selected node.
• ros2 run <package> <node> --ros-args -r __node:=<new name> Run a node with a different name. This is useful because all nodes must have unique names.
• RQT (called by writing rqt or rqt_graph in terminal) - will launch a ROS GUI with a collection of plugins.
  • Plugins > Introspection > Node Graph draggable UI to see all nodes.
  • Change Nodes only to Nodes/Topic (all) and uncheck dead sinks, to see all topics running too.
• ros2 interface show example_interfaces/msg/String - view what is inside an interface.
• run News station test with publisher in cpp, and subscriber in python
  • ros2 run my_py_pkg robot_news_station
  • ros2 run my_py_pkg smartphone
  • ros2 run my_cpp_pkg robot_news_station
  • ros2 run my_cpp_pkg smartphone
• Show interface types using the interfaces commands;
  • ros2 interface show example_interfaces/msg/String
• get Average HZ frequency of a topic
  • ros2 topic hz /robot_news
• get bandwidth of a topic
  • ros2 topic bw /robot_news
• Publish to topic from terminal;
  • ros2 topic pub -r 10 /robot_news example_interfaces/msg/String "{data: 'hi' }"
• Remap topic at runtime:
  • ros2 run my_cpp_pkg robot_news_station --ros-args -r __node:=my_station -r robot_news:=my_news
    • -r __node:=my_station - Node name
    • -r robot_news:=my_news - will replace any strings in the code. In this case, this is the name of our topic.

Turtlesim

• Runnig turtlesim
  • ros2 run turtlesim turtlesim_node - the visual turtle
  • ros2 run turtlesim turtle_teleop_key - turtle controller
  • ros2 interface show geometry_msgs/msg/Twist - the topic message type that controls the turtle

Number Counter Examples

- number_publisher - a node that publishes a number (always 1.)
- number_counter - a node that subscribes to `number_publisher` and adds 1 to it, every time it recieves something from it. It will then publish the added value

How to run Number Counter Example

• ros2 run my_cpp_pkg number_publisher
• ros2 run my_cpp_pkg number_counter
• You can inspect them in rqt_graph

Things to remember

General

• after building your package, before you can run it, remember to source ~/.bashrc.
• in order for --symlink-install to work, the file needs to be an executable, so run chmod +x NODE_NAME_HERE to make sure it is.
• you might want to make an alias to this command, as you will use it alot: colcon build --packages-select {package_name} && source ~/.bashrc && ros2 run {package_name} {node_name}
• when building, make sure you're in the ros2_ws directory, and not in the root.

Python specific

• When creating your package, remember to include your node inside entry_node and console_scripts. eg:

      # ...
      tests_require=['pytest'],
      entry_points={
          'console_scripts': [
              "py_node = my_py_pkg.my_first_node:main"
          ],
      },