Introduction to ROS2

Part 1: Getting started

Where to find ROS 2 distributions

https://docs.ros.org/

Getting started tutorials

https://docs.ros.org/en/foxy/Tutorials.html

Quick overview of Docker

Check out docker/Dockerfile

Create a workspace

https://docs.ros.org/en/foxy/Tutorials/Beginner-Client-Libraries/Creating-A-Workspace/Creating-A-Workspace.html

ros2 pkg create --build-type ament_python --node-name example_node example_package

.
└── example_package
    ├── example_package
    │   ├── __init__.py
    │   └── example_node.py
    ├── package.xml
    ├── resource
    │   └── example_package
    ├── setup.cfg
    ├── setup.py
    └── test
        ├── test_copyright.py
        ├── test_flake8.py
        └── test_pep257.py

4 directories, 9 files

Build a package:

colcon build

Source the built binaries:

. install/setup.bash

Run a node:

ros2 run my_package my_node

Part 2: Topics

Create a new docker instance

and Open 2 windows:

docker exec -it optimistic_wu bash

Create a topic:

Build topic publisher class under example_topic/example_publisher.py

Highlights:

self.create_publisher(String, 'topic', 10)

self.create_timer(period, self.callback)

import rclpy
from rclpy.node import Node

from std_msgs.msg import String


class ExamplePublisher(Node):

    def __init__(self):
        super().__init__('example_publisher')
        self.publisher_ = self.create_publisher(String, 'topic', 10)
        timer_period = 0.5  # seconds
        self.timer = self.create_timer(timer_period, self.timer_callback)
        self.i = 0

    def timer_callback(self):
        msg = String()
        msg.data = 'Hello World: %d' % self.i
        self.publisher_.publish(msg)
        # self.get_logger().info('Publishing: "%s"' % msg.data)
        self.i += 1


def main(args=None):
    rclpy.init(args=args)

    example_publisher = ExamplePublisher()

    rclpy.spin(example_publisher)

    example_publisher.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

Dont forget to add entry to setup.cfg!

    entry_points={
        'console_scripts': [
            'example_publisher = example_topic.example_node:main',
            'example_subscriber = example_topic.example_subscriber:main',
        ],
    },

Create a subscriber:

Build topic subscriber class under example_topic/example_publisher.py

Highlights:

self.subscription = self.create_subscription(String, 'topic', listener_callback, 10)

import rclpy
from rclpy.node import Node

from std_msgs.msg import String


class ExampleSubscriber(Node):

    def __init__(self):
        super().__init__('example_subscriber')
        self.subscription = self.create_subscription(
            String,
            'topic',
            self.listener_callback,
            10)
        self.subscription  # prevent unused variable warning

    def listener_callback(self, msg):
        self.get_logger().info('I heard: "%s"' % msg.data)


def main(args=None):
    rclpy.init(args=args)

    example_subscriber = ExampleSubscriber()

    rclpy.spin(example_subscriber)

    # Destroy the node explicitly
    # (optional - otherwise it will be done automatically
    # when the garbage collector destroys the node object)
    minimal_subscriber.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

Create a service:

Build service class under example_service/example_service.py

Highlights:

self.create_service(AddTwoInts, 'add_two_ints', self.add_two_ints_callback)

add_two_ints_callback(self, request, response):

from example_interfaces.srv import AddTwoInts

import rclpy
from rclpy.node import Node


class MinimalService(Node):

    def __init__(self):
        super().__init__('minimal_service')
        self.srv = self.create_service(AddTwoInts, 'add_two_ints', self.add_two_ints_callback)

    def add_two_ints_callback(self, request, response):
        response.sum = request.a + request.b
        self.get_logger().info('Incoming request\na: %d b: %d' % (request.a, request.b))

        return response


def main(args=None):
    rclpy.init(args=args)

    minimal_service = MinimalService()

    rclpy.spin(minimal_service)

    rclpy.shutdown()


if __name__ == '__main__':
    main()

Call the service from the command line:

ros2 service list

ros2 service call /add_two_ints ex/srv/AddTwoInts "{a: 32,b: 90}"

from example_interfaces.srv import AddTwoInts

import rclpy
from rclpy.node import Node


class ExampleService(Node):

    def __init__(self):
        super().__init__('minimal_service')
        self.srv = self.create_service(AddTwoInts, 'add_two_ints', self.add_two_ints_callback)

    def add_two_ints_callback(self, request, response):
        response.sum = request.a + request.b
        self.get_logger().info('Incoming request\na: %d b: %d' % (request.a, request.b))

        return response


def main(args=None):
    rclpy.init(args=args)

    example_service = ExampleService()

    rclpy.spin(example_service)

    rclpy.shutdown()


if __name__ == '__main__':
    main()

Dont forget to add entry to setup.cfg!

ros2 run gazebo_ros spawn_entity.py -file /workspace/models/iris_with_standoffs/model.sdf -entity drone

/workspace/ardupilot/Tools/autotest/sim_vehicle.py -v ArduCopter -f gazebo-iris -I 1

ros2 run mavros mavros_node fcu_url:=udp://0.0.0.0:14561@14565 target_component_id:=1 fcu_protocol:=v2.0

ros2 service call /drone1/mavros/set_mode mavros_msgs/srv/SetMode "{custom_mode: GUIDED}"
ros2 service call /drone1/mavros/cmd/arming  mavros_msgs/srv/CommandBool "{value: true}"
ros2 service call /drone1/mavros/cmd/takeoff mavros_msgs/srv/CommandTOL "{altitude: 1}"
ros2 service call /drone1/mavros/cmd/land mavros_msgs/srv/CommandTOL "{}"
ros2 topic pub /drone1/mavros/setpoint_position/local geometry_msgs/msg/PoseStamped "{pose:{position: {x: 1, z: 5}}}"
ros2 topic pub /drone1/mavros/setpoint_position/local geometry_msgs/msg/PoseStamped "{pose:{position: {x: -20, y: -20, z: 1}}}"
ros2 service call /drone1/mavros/set_mode mavros_msgs/srv/SetMode "{custom_mode: RTL}"