ros2_control "Error configuring controller" and controller state "finalized"

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Hello community,

I want to implement a differential drive controller on a simulated diff drive robot using ros2_control. After I spawn my robot I run the launch file that starts the controllers (ros2 launch diffbot_sim diffbot_controllers.launch.py) and I get the following error log (cut short for brevity):

[ros2-1] Sucessfully loaded controller joint_state_broadcaster into state active
...
[ros2-3] Error configuring controller
[ERROR] [ros2-3]: process has died [pid 7817, exit code 1, cmd 'ros2 control load_controller --set-state start diff_drive_controller'].

And the output of ros2 control list_controllers is:

joint_state_broadcaster[joint_state_broadcaster/JointStateBroadcaster] active
diff_drive_controller[diff_drive_controller/DiffDriveController] finalized

The error log is pointing me to an error in the configuration file. Left and right wheel names seem to be ok. How do I debug this? Could you point me in the right direction? Thank you for any help you can offer.

Regards, Roberto

launch file:

import os

from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.substitutions import Command, FindExecutable, PathJoinSubstitution
from launch.actions import ExecuteProcess, IncludeLaunchDescription, RegisterEventHandler
from launch.event_handlers import OnProcessExit
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch_ros.actions import Node
from launch_ros.substitutions import FindPackageShare


def generate_launch_description():

    load_joint_state_controller = ExecuteProcess(
        cmd=['ros2', 'control', 'load_controller', '--set-state', 'start',
             'joint_state_broadcaster'],
        output='screen'
    )

    load_diff_drive_controller = ExecuteProcess(
        cmd=['ros2', 'control', 'load_controller', '--set-state', 'start',
             'diff_drive_controller'],
        output='screen'
    )


    return LaunchDescription([
        load_joint_state_controller,
        RegisterEventHandler(
            event_handler=OnProcessExit(
                target_action=load_joint_state_controller,
                on_exit=[load_diff_drive_controller],
            )
        ),
    ])

.yaml config file

controller_manager:
  ros__parameters:
    update_rate: 50  # Hz

    joint_state_broadcaster:
      type: joint_state_broadcaster/JointStateBroadcaster

    diff_drive_controller:
      type: diff_drive_controller/DiffDriveController

diffbot_base_controller:
  ros__parameters:
    left_wheel_names: ["left_wheel_joint"]
    right_wheel_names: ["right_wheel_joint"]

    wheel_separation: 0.10
    #wheels_per_side: 1  # actually 2, but both are controlled by 1 signal
    wheel_radius: 0.015

    wheel_separation_multiplier: 1.0
    left_wheel_radius_multiplier: 1.0
    right_wheel_radius_multiplier: 1.0

    publish_rate: 50.0
    odom_frame_id: odom
    base_frame_id: base_link
    pose_covariance_diagonal : [0.001, 0.001, 0.001, 0.001, 0.001, 0.01]
    twist_covariance_diagonal: [0.001, 0.001, 0.001, 0.001, 0.001, 0.01]

    open_loop: true
    enable_odom_tf: true

    cmd_vel_timeout: 0.5
    #publish_limited_velocity: true
    use_stamped_vel: false
    #velocity_rolling_window_size: 10

    # Velocity and acceleration limits
    # Whenever a min_* is unspecified, default to -max_*
    linear.x.has_velocity_limits: true
    linear.x.has_acceleration_limits: true
    linear.x.has_jerk_limits: false
    linear.x.max_velocity: 1.0
    linear.x.min_velocity: -1.0
    linear.x.max_acceleration: 1.0
    linear.x.max_jerk: 0.0
    linear.x.min_jerk: 0.0

    angular.z.has_velocity_limits: true
    angular.z.has_acceleration_limits: true
    angular.z.has_jerk_limits: false
    angular.z.max_velocity: 1.0
    angular.z.min_velocity: -1.0
    angular.z.max_acceleration: 1.0
    angular.z.min_acceleration: -1.0
    angular.z.max_jerk: 0.0
    angular.z.min_jerk: 0.0

ros2_control XML tags:

  <ros2_control name="diff_drive" type="system">

  <hardware>
      <plugin>gazebo_ros2_control/GazeboSystem</plugin>
  </hardware>

  <joint name="left_wheel_joint">
    <command_interface name="velocity">
      <param name="min">-1</param>
      <param name="max">1</param>
    </command_interface>
    <state_interface name="position"/>
    <state_interface name="velocity"/>
    <state_interface name="effort"/>
  </joint>

  <joint name="right_wheel_joint">
    <command_interface name="velocity">
      <param name="min">-1</param>
      <param name="max">1</param>
    </command_interface>
    <state_interface name="position"/>
    <state_interface name="velocity"/>
    <state_interface name="effort"/>
  </joint>

</ros2_control>