ROS2 Application Not Able to Get Create3 Odom

[drpjm]

I have a perplexing issue and cannot find this issue in my internet searches. I want to use the Create3's odom data. I get the output on the terminal of the Locobot's via ros2 topic echo no problem.

But my application is subscribing to this topic and the callback is not firing. An image from my callback within my application is shown as well as my node's info:

I decided to modify the ROS2 Minimal Subscriber example and I have the same issue: the callback does not fire! Here is the simple node:

import rclpy
from rclpy.node import Node
from nav_msgs.msg import Odometry

class MinimalSubscriber(Node):

    def __init__(self):
        super().__init__('minimal_subscriber')
        self.subscription = self.create_subscription(
            Odometry,
            '/locobot/mobile_base/odom',
            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)

    minimal_subscriber = MinimalSubscriber()

    rclpy.spin(minimal_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()

Any thoughts as to why this is happening? All code is running directly on the Locobot's NUC. All of my other non-Create3 topics are handled just fine.

EDIT: I tested this with other Create3 topics, like /locobot/mobile_base/battery_state and it has the same problem. However, if I launch one of my other sensor nodes that runs on the NUC and modify the MinimalPublisher above, it works just fine. And for another test, I performed command line publications onto these Create3 specific topics and my callbacks in rclpy fire just fine!

[drpjm]

Turns out this is a sneaky issue: the reason I cannot read odom is that in ROS2 galactic, topic QoS mismatches are not displayed. So, it silently fails when you subscribe to a topic with different QoS. To solve this issue, you should subscribe to the sensor data from the Create3 with:

from rclpy.qos import qos_profile_sensor_data

class SomeNode(Node)
    def __init__(self):
        self.odom_subscriber = self.create_subscription(
            Odometry, "/locobot/mobile_base/odom",
            self._on_odom,
            qos_profile_sensor_data)