Hey all! I'm having some problems with Gazebo. I'm using ROS2 foxy on UBUNTU 20.04.5 LTS with Gazebo installed via ros-foxy-gazebo. I made an URDF model on a differential drive robot, with a launch file to run gazebo and spawn the robot. Even though, when launching the file, it appears on the terminal that the diffdrive is advertising the /odom and publishing the tf between odom frame and baselink, i cannot find the frame odom in RVIZ2. Moreover, when echoing the /odom topic i have no results. Finally, in the viewframes the odom frame doesn't appear. I guess that i did the correct launch file with the diffdrive control plugin and the good parameters. Here below the files. Launch file:

import os

from ament_index_python.packages import get_package_share_directory


from launch import LaunchDescription
from launch.actions import IncludeLaunchDescription
from launch.launch_description_sources import PythonLaunchDescriptionSource

from launch_ros.actions import Node


def generate_launch_description():

    # Include the robot_state_publisher launch file, provided by our own package. Force sim time to be enabled
    # !!! MAKE SURE YOU SET THE PACKAGE NAME CORRECTLY !!!

    package_name = 'package_test'  # <--- CHANGE ME

    rsp = IncludeLaunchDescription(
        PythonLaunchDescriptionSource([os.path.join(
            get_package_share_directory(
                package_name), 'launch', 'rsp.launch.py'
        )]), launch_arguments={'use_sim_time': 'true'}.items()
    )
# Include the Gazebo launch file, provided by the gazebo_ros package
gazebo = IncludeLaunchDescription(
    PythonLaunchDescriptionSource([os.path.join(
        get_package_share_directory('gazebo_ros'), 'launch', 'gazebo.launch.py')]),
)

# Run the spawner node from the gazebo_ros package. The entity name doesn't really matter if you only have a single robot.
spawn_entity = Node(package='gazebo_ros', executable='spawn_entity.py',
                    arguments=['-topic', 'robot_description',
                               '-entity', 'my_bot'],
                    output='screen')

# Launch them all!
return LaunchDescription([
    rsp,
    gazebo,
    spawn_entity,
])

Gazebo plugin:

<?xml version="1.0"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro"  name="robot">

   <gazebo>
        <plugin name="diff_drive" filename="libgazebo_ros_diff_drive.so">
            <!-- Wheel info-->
            <left_joint>left_wheel_joint</left_joint>
            <right_joint>right_wheel_joint</right_joint>
            <wheel_separation>0.35</wheel_separation>
            <wheel_diameter>0.1</wheel_diameter>

            <!-- Limits-->
            <max_wheel_torque>200</max_wheel_torque>
            <max_wheel_acceleration>10.0</max_wheel_acceleration>

            <!-- Output-->
            <odometry_frame>odom</odometry_frame>
            <robot_base_frame>base_link</robot_base_frame>

            <publish_odom>true</publish_odom> 
            <publish_odom_tf>true</publish_odom_tf> 
            <publish_wheel_tf>true</publish_wheel_tf> 

        </plugin>


     </gazebo>

</robot>

URDF file:

<?xml version="1.0"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro" >

    <xacro:include filename="inertial_macros.xacro"/>

    <material name="white">
        <color rgba="1 1 1 1" />
    </material>

    <material name="orange">
        <color rgba="1 0.3 0.1 1"/>
    </material>

    <material name="blue">
        <color rgba="0.2 0.2 1 1"/>
    </material>

    <material name="black">
        <color rgba="0 0 0 1"/>
    </material>

    <!-- BASE LINK -->

    <link name="base_link">

    </link>


    <!-- CHASSIS LINK -->

    <joint name="chassis_joint" type="fixed">
        <parent link="base_link"/>
        <child link="chassis"/>
        <origin xyz="-0.1 0 0"/>
    </joint>

    <link name="chassis">
        <visual>
            <origin xyz="0.15 0 0.075"/>
            <geometry>
                <box size="0.3 0.3 0.15"/>
            </geometry>
            <material name="white"/>
        </visual>
        <collision>
            <origin xyz="0.15 0 0.075"/>
            <geometry>
                <box size="0.3 0.3 0.15"/>
            </geometry>
        </collision>

    </link>

    <gazebo reference="right_wheel">
        <material>Gazebo/White</material>
    </gazebo>
    <!-- LEFT WHEEL LINK -->

    <joint name="left_wheel_joint" type="continuous">
        <parent link="base_link"/>
        <child link="left_wheel"/>
        <origin xyz="0 0.175 0" rpy="-${pi/2} 0 0" />
        <axis xyz="0 0 1"/>
    </joint>

    <link name="left_wheel">
        <visual>
            <geometry>
                <cylinder radius="0.05" length="0.04"/>
            </geometry>
            <material name="blue"/>
        </visual>
        <collision>
            <geometry>
                <cylinder radius="0.05" length="0.04"/>
            </geometry>
        </collision>
        <xacro:inertial_cylinder mass="0.1" length="0.04" radius="0.05">
            <origin xyz="0 0 0" rpy="0 0 0"/>
        </xacro:inertial_cylinder>
    </link>

     <gazebo reference="left_wheel">
        <material>Gazebo/Blue</material>
    </gazebo>

    <!-- RIGHT WHEEL LINK -->

    <joint name="right_wheel_joint" type="continuous">
        <parent link="base_link"/>
        <child link="right_wheel"/>
        <origin xyz="0 -0.175 0" rpy="${pi/2} 0 0" />
        <axis xyz="0 0 -1"/>
    </joint>

    <link name="right_wheel">
        <visual>
            <geometry>
                <cylinder radius="0.05" length="0.04"/>
            </geometry>
            <material name="blue"/>
        </visual>
        <collision>
            <geometry>
                <cylinder radius="0.05" length="0.04"/>
            </geometry>
        </collision>
        <xacro:inertial_cylinder mass="0.1" length="0.04" radius="0.05">
            <origin xyz="0 0 0" rpy="0 0 0"/>
        </xacro:inertial_cylinder>
    </link>

    <gazebo reference="right_wheel">
        <material>Gazebo/Blue</material>
    </gazebo>
    <!-- CASTER WHEEL LINK -->

    <joint name="caster_wheel_joint" type="fixed">
        <parent link="chassis"/>
        <child link="caster_wheel"/>
        <origin xyz="0.24 0 0"/>
    </joint>


    <link name="caster_wheel">
        <visual>
            <geometry>
                <sphere radius="0.05"/>
            </geometry>
            <material name="black"/>
        </visual>
        <collision>
            <geometry>
                <sphere radius="0.05"/>
            </geometry>
        </collision>
        <xacro:inertial_sphere mass="0.1" radius="0.05">
            <origin xyz="0 0 0" rpy="0 0 0"/>
        </xacro:inertial_sphere>
    </link>

    <gazebo reference="caster_wheel">
        <material>Gazebo/Black</material>
    </gazebo>
</robot>

the file rsp.launch

import os

from ament_index_python.packages import get_package_share_directory

from launch import LaunchDescription
from launch.substitutions import LaunchConfiguration
from launch.actions import DeclareLaunchArgument
from launch_ros.actions import Node

import xacro


def generate_launch_description():

    # Check if we're told to use sim time
use_sim_time = LaunchConfiguration('use_sim_time')

# Process the URDF file
pkg_path = '/home/andi/dev_ws/src/package_test'
xacro_file = os.path.join(pkg_path, 'description', 'robot.urdf.xacro')
robot_description_config = xacro.process_file(xacro_file)

# Create a robot_state_publisher node
params = {'robot_description': robot_description_config.toxml(),
          'use_sim_time': use_sim_time}
node_robot_state_publisher = Node(
    package='robot_state_publisher',
    executable='robot_state_publisher',
    output='screen',
    parameters=[params]
)

# Launch!
return LaunchDescription([
    DeclareLaunchArgument(
        'use_sim_time',
        default_value='true',
        description='Use sim time if true'),

    node_robot_state_publisher
])

Finally, this is the output on the terminal when running the launch file:

[robot_state_publisher-1] Parsing robot urdf xml string.
[robot_state_publisher-1] Link chassis had 1 children
[robot_state_publisher-1] Link caster_wheel had 0 children
[robot_state_publisher-1] Link left_wheel had 0 children
[robot_state_publisher-1] Link right_wheel had 0 children
[robot_state_publisher-1] [INFO] [1671286215.419064105] [robot_state_publisher]: got segment base_link
[robot_state_publisher-1] [INFO] [1671286215.419196314] [robot_state_publisher]: got segment caster_wheel
[robot_state_publisher-1] [INFO] [1671286215.419212848] [robot_state_publisher]: got segment chassis
[robot_state_publisher-1] [INFO] [1671286215.419220446] [robot_state_publisher]: got segment left_wheel
[robot_state_publisher-1] [INFO] [1671286215.419226922] [robot_state_publisher]: got segment right_wheel
[spawn_entity.py-4] [INFO] [1671286215.849066532] [spawn_entity]: Spawn Entity started
[spawn_entity.py-4] [INFO] [1671286215.849747418] [spawn_entity]: Loading entity published on topic robot_description
[spawn_entity.py-4] [INFO] [1671286215.851772580] [spawn_entity]: Waiting for entity xml on robot_description
[spawn_entity.py-4] [INFO] [1671286215.864727286] [spawn_entity]: Waiting for service /spawn_entity, timeout = 30
[spawn_entity.py-4] [INFO] [1671286215.865147088] [spawn_entity]: Waiting for service /spawn_entity
[spawn_entity.py-4] [INFO] [1671286219.387568115] [spawn_entity]: Calling service /spawn_entity
[gzserver-2] Warning [parser_urdf.cc:1130] multiple inconsistent <name> exists due to fixed joint reduction overwriting previous 
value [Gazebo/White] with [Gazebo/Blue].
[spawn_entity.py-4] [INFO] [1671286219.677514717] [spawn_entity]: Spawn status: SpawnEntity: Successfully spawned entity 
[my_bot]
[gzserver-2] [INFO] [1671286219.744421519] [diff_drive]: Wheel pair 1 separation set to [0.350000m]
[gzserver-2] [INFO] [1671286219.746272383] [diff_drive]: Wheel pair 1 diameter set to [0.100000m]
[gzserver-2] [INFO] [1671286219.751120486] [diff_drive]: Subscribed to [/cmd_vel]
[gzserver-2] [INFO] [1671286219.759056484] [diff_drive]: Advertise odometry on [/odom]
[gzserver-2] [INFO] [1671286219.763536717] [diff_drive]: Publishing odom transforms between [odom] and [base_link]
[gzserver-2] [INFO] [1671286219.763606642] [diff_drive]: Publishing wheel transforms between [base_link], [left_wheel_joint] 
and [right_wheel_joint]
[INFO] [spawn_entity.py-4]: process has finished cleanly [pid 128488]