ROS 2¶

ROS 2 (Robot Operating System 2) is an open source software development kit for robotics applications. The purpose of ROS 2 is to offer a standard software platform to developers across industries that will carry them from research and prototyping through to deployment and production. ROS 2 builds on the success of ROS 1, which is used today in myriad robotics applications around the world

Simulation¶

craete an accont on : https://www.theconstruct.ai

Open the Rosjects: https://app.theconstruct.ai/l/6400c71b

update the system

sudo apt update
sudo apt upgrade

install ROS2 Humble https://docs.ros.org/en/humble/Installation/Ubuntu-Install-Debs.html

clone project

cd ~/ros2_ws/src
git clone https://github.com/MohammadRobot/vmxpi_ros2.git

build project

cd ~/ros2_ws && colcon build --packages-select vmxpi_ros2 && source install/setup.bash

To launch the simulation with Gazebo:

ros2 launch vmxpi_ros2 diffbot_gazebo_classic.launch.py gui:=true use_gazebo_classic:=true

To conrol the robot by Keyboard run the following command in the new termnial

os2 run teleop_twist_keyboard teleop_twist_keyboard --ros-args -p stamped:=True --remap cmd_vel:=/diffbot_base_controller/cmd_vel

if not moving run the following command

sudo apt update
sudo apt install ros-humble-teleop-twist-keyboard

you must get ros-humble-teleop-twist-keyboard version (2.4.0) or newer

ROS 2 package¶

ROS2 uses packages to organize its programs. Think of a package as all the files that a specific ROS program contains; all its CPP files, Python files, configuration files, compilation files, launch files, and parameter files. Also, organizing your ROS2 programs in packages makes sharing them with other developers/users much easier.

Every package will have the following structure of files and folders:

launch folder: Contains launch files
src folder: Contains source files (CPP, Python)
CMakeLists.txt: List of Cmake rules for compilation
package.xml: Package metadata and dependencies

Create a Package¶

Go to ROS2 Workspace:

cd ~/ros2_ws/src

Create Package by runing this command:

ros2 pkg create topic_publisher_pkg --build-type ament_cmake --dependencies rclcpp std_msgs

To compile the package:

cd ~/ros2_ws/
colcon build

Source setup.bash from the install folder so that ROS can find the packages in the workspace

source install/setup.bash

To list ROS2 Packages

ros2 pkg list

Launch File¶

To run ROS 2 program you can use launch file the by runing the following command:

ros2 launch <package_name> <launch_file>

To create launch file

cd ~/ros2_ws/src/topic_publisher_pkg
mkdir launch
cd launch
touch simple_topic_publisher.launch.py
chmod +x simple_topic_publisher.launch.py

Sample code of launch file

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='topic_publisher_pkg',
            executable='simple_publisher_node',
            output='screen'),
    ])

Source File (src)¶

Create a C++ file in the src directory of topic_publisher_pkg

cd ~/ros2_ws/src/topic_publisher_pkg/src
touch simple_topic_publisher.cpp

Copy the following code:

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/int32.hpp"
#include <chrono>

using namespace std::chrono_literals;

/* This example creates a MohammadRobot
class SimplePublisher : public rclcpp::Node
{
public:
  SimplePublisher()
  : Node("simple_publisher"), count_(0)
  {
    publisher_ = this->create_publisher<std_msgs::msg::Int32>("counter", 10);
    timer_ = this->create_wall_timer(
      500ms, std::bind(&SimplePublisher::timer_callback, this));
  }

private:
  void timer_callback()
  {
    auto message = std_msgs::msg::Int32();
    message.data = count_;
    count_++;
    publisher_->publish(message);
  }
  rclcpp::TimerBase::SharedPtr timer_;
  rclcpp::Publisher<std_msgs::msg::Int32>::SharedPtr publisher_;
  size_t count_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<SimplePublisher>());
  rclcpp::shutdown();
  return 0;
}

CMakeLists.txt file¶

add the following code to CMakeLists.txt befor ament_package() line

add_executable(simple_publisher_node src/simple_topic_publisher.cpp)
ament_target_dependencies(simple_publisher_node rclcpp std_msgs)

install(TARGETS
   simple_publisher_node
   DESTINATION lib/${PROJECT_NAME}
 )

# Install launch files.
install(DIRECTORY
  launch
  DESTINATION share/${PROJECT_NAME}/
)

# ament_package()

Compiling the package¶

To compile the package run the following command:

cd ~/ros2_ws/
colcon build
source install/setup.bash

Visualize Data¶

RVIZ¶

To open rviz run the following commmad

rviz2

rqt_graph¶

To open rqt_graph run the following commmad

rqt_graph