Build a Publisher Node

Create:

robotnix_pubsub/robotnix_pubsub/talker.py

Use this course adaptation of the official rclpy beginner publisher pattern:

import rclpy
from rclpy.node import Node
from std_msgs.msg import String


class RobotnixTalker(Node):
    def __init__(self):
        super().__init__('robotnix_talker')
        self.publisher = self.create_publisher(String, 'student_chatter', 10)
        self.count = 0
        self.timer = self.create_timer(1.0, self.publish_message)

    def publish_message(self):
        msg = String()
        msg.data = f'Robotnix message {self.count}'
        self.publisher.publish(msg)
        self.get_logger().info(f'Publishing: {msg.data}')
        self.count += 1


def main(args=None):
    rclpy.init(args=args)
    node = RobotnixTalker()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()

Trace the ROS responsibilities

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

declares a publisher using std_msgs/msg/String on the student_chatter topic.

self.create_timer(1.0, self.publish_message)

schedules the callback repeatedly.

The callback constructs a message, fills msg.data, publishes it, and logs evidence.

Checkpoint

Before running anything, predict:

• node name;
• topic name;
• message type;
• approximate publication interval.