I'm trying to make an environment for a simulation with a robotic arm (github repo of the 3 packages). Ubuntu 20 with ros foxy. This repo when running

ros2 launch learm_ros2 follower.launch.py
ros2 launch learm_ros2 run.launch.py

Allows you to visualise the robotic arm in rviz and move it (only if the real one is connected,) moving as well the real robotic arm. I wanted to start adding the robot into gazebo to proceed with simulations, seeing that one of the packages is called moveit_config

I modified run.launch.py in order to open gazebo, an empty world with a model (a table from the gazebo library), and I spawn the robot on top. The first thing I noticed is that the urdf being used is in the other package, description package, and has a xacro file as well. Which for the follower script and rviz, worked fine. But for gazebo, I need intertial and collision values, which are not in this urdf but happen to be in the urdf that is in main package

 urdf = os.path.join(

And the structure:

robot name is: LeArm
---------- Successfully Parsed XML ---------------
root Link: base_link has 1 child(ren)
    child(1):  shoulder_link
        child(1):  humerus_link
            child(1):  forearm_link
                child(1):  wrist_link
                    child(1):  hand_link
                        child(1):  grip_left_link
                            child(1):  finger_left_link
                        child(2):  grip_right_link
                            child(1):  finger_right_link
                        child(3):  tendon_left_link
                        child(4):  tendon_right_link

This is my modified run.launch.py

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument, ExecuteProcess
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node

def generate_launch_description():
    gui = LaunchConfiguration('gui', default='true')
    rviz_config = os.path.join(

    urdf = os.path.join(

    with open(urdf, 'r') as infp:
        robot_desc = infp.read()
    gazebo_world_path = os.path.join(
        'worlds', 'table_world.world')  
    return LaunchDescription([
            cmd=['gazebo', '--verbose', gazebo_world_path, '-s', 'libgazebo_ros_factory.so', '-u'],
            package='gazebo_ros', executable='spawn_entity.py',
            arguments=['-entity', 'robot_name', '-topic', 'robot_description', '-z', '1.04'],  
            package='joint_state_publisher' + '_gui' if gui else '',
            executable='joint_state_publisher' + '_gui' if gui else '',
            parameters=[{'robot_description': robot_desc}],
            package='joint_state_publisher', executable='joint_state_publisher',
            parameters=[{'robot_description': robot_desc}],
            parameters=[{'robot_description': robot_desc}],
            parameters=[{'robot_description': robot_desc}],
            arguments=['-d', rviz_config]),
        # Node(
        #     package='gazebo_ros',
        #     executable='gazebo',
        #     name='gazebo',
        #     output='screen',
        #     arguments=['-e', '-s', 'libgazebo_ros_controller_manager.so']),

robot starting the simulation robot falls on itself

I added more mass to the base so it would not flip as well. This is what the log gives me. I can already see a warning on deleting a connection right after creation, and the gazebo_ros2_control errors of yaml configuration files.

ros2 launch learm_ros2 run.launch.py 
/opt/ros/foxy/bin/ros2:6: DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
  from pkg_resources import load_entry_point
[INFO] [launch]: All log files can be found below /home/mk/.ros/log/2024-04-04-23-40-36-177870-mk-5490
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [gazebo-1]: process started with pid [5492]
[INFO] [spawn_entity.py-2]: process started with pid [5494]
[INFO] [joint_state_publisher_gui-3]: process started with pid [5496]
[INFO] [joint_state_publisher-4]: process started with pid [5498]
[INFO] [robot_state_publisher-5]: process started with pid [5500]
[INFO] [rviz2-6]: process started with pid [5511]
[robot_state_publisher-5] Parsing robot urdf xml string.
[robot_state_publisher-5] The root link base_link has an inertia specified in the URDF, but KDL does not support a root link with an inertia.  As a workaround, you can add an extra dummy link to your URDF.
[robot_state_publisher-5] Link shoulder_link had 1 children
[robot_state_publisher-5] Link humerus_link had 1 children
[robot_state_publisher-5] Link forearm_link had 1 children
[robot_state_publisher-5] Link wrist_link had 1 children
[robot_state_publisher-5] Link hand_link had 4 children
[robot_state_publisher-5] Link grip_left_link had 1 children
[robot_state_publisher-5] Link finger_left_link had 0 children
[robot_state_publisher-5] Link grip_right_link had 1 children
[robot_state_publisher-5] Link finger_right_link had 0 children
[robot_state_publisher-5] Link tendon_left_link had 0 children
[robot_state_publisher-5] Link tendon_right_link had 0 children
[robot_state_publisher-5] [INFO] [1712266836.456161261] [robot_state_publisher]: got segment base_link
[robot_state_publisher-5] [INFO] [1712266836.456240671] [robot_state_publisher]: got segment finger_left_link
[robot_state_publisher-5] [INFO] [1712266836.456249049] [robot_state_publisher]: got segment finger_right_link
[robot_state_publisher-5] [INFO] [1712266836.456253881] [robot_state_publisher]: got segment forearm_link
[robot_state_publisher-5] [INFO] [1712266836.456258395] [robot_state_publisher]: got segment grip_left_link
[robot_state_publisher-5] [INFO] [1712266836.456262773] [robot_state_publisher]: got segment grip_right_link
[robot_state_publisher-5] [INFO] [1712266836.456267075] [robot_state_publisher]: got segment hand_link
[robot_state_publisher-5] [INFO] [1712266836.456271369] [robot_state_publisher]: got segment humerus_link
[robot_state_publisher-5] [INFO] [1712266836.456275698] [robot_state_publisher]: got segment shoulder_link
[robot_state_publisher-5] [INFO] [1712266836.456280086] [robot_state_publisher]: got segment tendon_left_link
[robot_state_publisher-5] [INFO] [1712266836.456284457] [robot_state_publisher]: got segment tendon_right_link
[robot_state_publisher-5] [INFO] [1712266836.456288771] [robot_state_publisher]: got segment wrist_link
[gazebo-1] Gazebo multi-robot simulator, version 11.11.0
[gazebo-1] Copyright (C) 2012 Open Source Robotics Foundation.
[gazebo-1] Released under the Apache 2 License.
[gazebo-1] http://gazebosim.org
[spawn_entity.py-2] [INFO] [1712266836.811201907] [spawn_entity]: Spawn Entity started
[spawn_entity.py-2] [INFO] [1712266836.812114364] [spawn_entity]: Loading entity published on topic robot_description
[spawn_entity.py-2] [INFO] [1712266836.815611701] [spawn_entity]: Waiting for entity xml on robot_description
[spawn_entity.py-2] [INFO] [1712266836.828088416] [spawn_entity]: Waiting for service /spawn_entity, timeout = 30
[spawn_entity.py-2] [INFO] [1712266836.828809548] [spawn_entity]: Waiting for service /spawn_entity
[rviz2-6] [INFO] [1712266836.836382659] [rviz2]: Stereo is NOT SUPPORTED
[rviz2-6] [INFO] [1712266836.836553267] [rviz2]: OpenGl version: 4.3 (GLSL 4.3)
[gazebo-1] Gazebo multi-robot simulator, version 11.11.0
[gazebo-1] Copyright (C) 2012 Open Source Robotics Foundation.
[gazebo-1] Released under the Apache 2 License.
[gazebo-1] http://gazebosim.org
[rviz2-6] [INFO] [1712266836.858854278] [rviz2]: Stereo is NOT SUPPORTED
[joint_state_publisher-4] [INFO] [1712266836.863734987] [joint_state_publisher]: Waiting for robot_description to be published on the robot_description topic...
[rviz2-6] Parsing robot urdf xml string.
[joint_state_publisher_gui-3] [INFO] [1712266836.996659300] [joint_state_publisher]: Centering
[gazebo-1] [INFO] [1712266837.412595584] [gazebo_ros_node]: ROS was initialized without arguments.
[spawn_entity.py-2] [INFO] [1712266837.833437326] [spawn_entity]: Calling service /spawn_entity
[spawn_entity.py-2] [INFO] [1712266838.127301269] [spawn_entity]: Spawn status: SpawnEntity: Successfully spawned entity [robot_name]
[INFO] [spawn_entity.py-2]: process has finished cleanly [pid 5494]
[gazebo-1] [Msg] Waiting for master.
[gazebo-1] [Msg] Connected to gazebo master @
[gazebo-1] [Msg] Publicized address:
[gazebo-1] [Wrn] [Event.cc:61] Warning: Deleting a connection right after creation. Make sure to save the ConnectionPtr from a Connect call
[gazebo-1] [INFO] [1712266838.773043703] [gazebo_ros2_control]: Loading gazebo_ros2_control plugin
[gazebo-1] [INFO] [1712266838.774871093] [gazebo_ros_control]: Starting gazebo_ros2_control plugin in namespace: /
[gazebo-1] [INFO] [1712266838.775045657] [gazebo_ros_control]: Starting gazebo_ros2_control plugin in ros 2 node: gazebo_ros_control
[gazebo-1] [ERROR] [1712266838.775078276] [gazebo_ros_control]: No parameter file provided. Configuration might be wrong
[gazebo-1] [ERROR] [1712266838.775138756] [gazebo_ros_control]: failed to parse input yaml file(s)

I searched on the learm_moveit_mode1.launch.py as it has a supposed environment to test the arm in gazebo as I understood it, and it configures yaml files. But this is confusing as well, as there are several yaml files for the robotic arm.


ls learm_ros2_description/config/
controllers.yaml       joint_limits.yaml  learm_servo.yaml    ros_controllers.yaml
fake_controllers.yaml  kinematics.yaml    ompl_planning.yaml


ls learm_ros2_moveit_config/config/
cartesian_limits.yaml  gazebo_controllers.yaml  sensors_3d.yaml                 stomp_planning.yaml
chomp_planning.yaml    LeArm.srdf               simple_moveit_controllers.yaml

I think I am either missing something quite basic in configuration or something with ros_controllers as a user in this site mentioned in a previous question.

This for example is ros_controllers.launch

<?xml version="1.0"?>

  <!-- Load joint controller configurations from YAML file to parameter server -->
  <rosparam file="$(find learm_ros2_moveit_config)/config/ros_controllers.yaml" command="load"/>

  <!-- Load the controllers -->
  <node name="controller_spawner" pkg="controller_manager" type="spawner" respawn="false"
    output="screen" args="arm_controller "/>


I do not understand why the robot seems to not update the joint_states publisher and acts strange, moving on its own (with the effects of gravity).


Taking @christoph-froehlich's advice, updating the system to Ubuntu 22 and ros2 humble did not change anything but it's always good to have it. Works the same. I think that the urdf needs the appropriate ros2-control tags with the existent joints. I will keep this updated.


2 Answers 2


Foxy is EOL, please use a still supported ROS distribution.

There were several fixes to gazebo_ros2_control regarding sagging robots.

By having a look on your console output: Why are you using joint_state_publisher_gui and gazebo at the same time? Both will publish on /joint_states if configured so.

  • $\begingroup$ Thank you very much! I will try with a supported ROS2 distro and update this! Sorry for the joint_state_publisher_gui, at some point I removed it and it didn't change any behavior so I kept it. $\endgroup$
    – M.K
    Commented Apr 5 at 9:06

It was a bit confusing at first so I will summarise how I fixed it:

  1. Create a ros2_control.xacro file that will be included in the urdf.xacro. Add the proper ros2-control tags with each joint necessary, and the gazebo-ros2-control. I tried with just the .urdf, but it was not working.
  2. Include it in the urdf.xacro. Use that for the robot_description. Remember, you will not use the .urdf, but the new .urdf.xacro

<xacro:include filename = "ros2_control.xacro" />

  1. PROPERLY define the yaml file, with the proper structure and ros__params.

        update_rate: 30
        use_sim_time: true
          type: joint_state_controller/JointStateController
          publish_rate: 50`
  2. ros2_control is now able to connect to the joints, the console will show you so. It can also be checked with roscontrol list_hardware_interfaces


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