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Hello Ros Community,

Description: I am currently in the process of developing a six-axis manipulator in ROS 2, utilizing MoveIt 2 for motion planning and Gazebo for simulation. Regrettably, I am facing a perplexing issue where the manipulator demonstrates peculiar behavior and instability, particularly when I employ position control as the command interface in Gazebo. To provide further clarity, I have included relevant visuals,launch files and urdf that can be accessed HERE.

I am using ROS2 Humble

To provide more context and aid in troubleshooting, here are the details related to the problem:

I am using the following launch file to start the Gazebo simulation and relevant ROS nodes:

ros2 launch hexa_bot_description gazebo.launch.py use_sim_time:=true

When executing the gazebo.launch.py launch file, the following log messages are displayed:

[INFO] [launch]: All log files can be found below /home/roskuttan/.ros/log/2023-05-31-08-57-10-218724-SILENT-KILLERED-1779 [INFO] [launch]: Default logging verbosity is set to INFO [INFO] [robot_state_publisher-1]: process started with pid [1780] [INFO] [joint_state_publisher-2]: process started with pid [1782] [INFO] [gzserver-3]: process started with pid [1784] [INFO] [gzclient-4]: process started with pid [1786] [INFO] [spawn_entity-5]: process started with pid [1788] [robot_state_publisher-1] [WARN] [1685503631.131584399] [kdl_parser]: 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-1] [INFO] [1685503631.131687999] [robot_state_publisher]: got segment JAW1_1 [robot_state_publisher-1] [INFO] [1685503631.131721599] [robot_state_publisher]: got segment JAW2_1 [robot_state_publisher-1] [INFO] [1685503631.131729199] [robot_state_publisher]: got segment JAW3_1 [robot_state_publisher-1] [INFO] [1685503631.131734199] [robot_state_publisher]: got segment JAW6_1 [robot_state_publisher-1] [INFO] [1685503631.131738899] [robot_state_publisher]: got segment Jaw4_1 [robot_state_publisher-1] [INFO] [1685503631.131743399] [robot_state_publisher]: got segment Jaw5_1 [robot_state_publisher-1] [INFO] [1685503631.131748099] [robot_state_publisher]: got segment NEMA_3_1 [robot_state_publisher-1] [INFO] [1685503631.131752799] [robot_state_publisher]: got segment NEMA_4_1 [robot_state_publisher-1] [INFO] [1685503631.131757499] [robot_state_publisher]: got segment NEMA_5_1 [robot_state_publisher-1] [INFO] [1685503631.131761999] [robot_state_publisher]: got segment Nema_1_1 [robot_state_publisher-1] [INFO] [1685503631.131766599] [robot_state_publisher]: got segment Nema_2_1 [robot_state_publisher-1] [INFO] [1685503631.131771199] [robot_state_publisher]: got segment Nema_6_1 [robot_state_publisher-1] [INFO] [1685503631.131775699] [robot_state_publisher]: got segment base_link [joint_state_publisher-2] [INFO] [1685503631.388555295] [joint_state_publisher]: Waiting for robot_description to be published on the robot_description topic... [spawn_entity-5] [INFO] [1685503631.573401292] [spawn_entity]: Spawn Entity started [spawn_entity-5] [INFO] [1685503631.573742092] [spawn_entity]: Loading entity published on topic robot_description [spawn_entity-5] /opt/ros/humble/local/lib/python3.10/dist-packages/rclpy/qos.py:307: UserWarning: DurabilityPolicy.RMW_QOS_POLICY_DURABILITY_TRANSIENT_LOCAL is deprecated. Use DurabilityPolicy.TRANSIENT_LOCAL instead. [spawn_entity-5] warnings.warn( [spawn_entity-5] [INFO] [1685503631.575072992] [spawn_entity]: Waiting for entity xml on robot_description [spawn_entity-5] [INFO] [1685503631.577393492] [spawn_entity]: Waiting for service /spawn_entity, timeout = 30 [spawn_entity-5] [INFO] [1685503631.577719191] [spawn_entity]: Waiting for service /spawn_entity [spawn_entity-5] [INFO] [1685503633.833226053] [spawn_entity]: Calling service /spawn_entity [spawn_entity-5] [INFO] [1685503634.191623847] [spawn_entity]: Spawn status: SpawnEntity: Successfully spawned entity [hexa_bot] [gzserver-3] [INFO] [1685503634.323934645] [gazebo_ros2_control]: Loading gazebo_ros2_control plugin [gzserver-3] [INFO] [1685503634.327896245] [gazebo_ros2_control]: Starting gazebo_ros2_control plugin in namespace: / [gzserver-3] [INFO] [1685503634.328103945] [gazebo_ros2_control]: Starting gazebo_ros2_control plugin in ros 2 node: gazebo_ros2_control [gzserver-3] [INFO] [1685503634.328150045] [gazebo_ros2_control]: Loading parameter files /home/roskuttan/hexa_bot_ws/install/hexa_bot_description/share/hexa_bot_description/config/hexa_bot.yaml [gzserver-3] [INFO] [1685503634.331047945] [gazebo_ros2_control]: connected to service!! robot_state_publisher [gzserver-3] [INFO] [1685503634.331636045] [gazebo_ros2_control]: Recieved urdf from param server, parsing... [gzserver-3] [INFO] [1685503634.339149145] [gazebo_ros2_control]: Loading joint: joint_1 [gzserver-3] [INFO] [1685503634.339277145] [gazebo_ros2_control]: State: [gzserver-3] [INFO] [1685503634.339294445] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339308445] [gazebo_ros2_control]: found initial value: 0.000000 [gzserver-3] [INFO] [1685503634.339355745] [gazebo_ros2_control]: velocity [gzserver-3] [INFO] [1685503634.339370145] [gazebo_ros2_control]: Command: [gzserver-3] [INFO] [1685503634.339380745] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339434745] [gazebo_ros2_control]: Loading joint: joint_2 [gzserver-3] [INFO] [1685503634.339447245] [gazebo_ros2_control]: State: [gzserver-3] [INFO] [1685503634.339457845] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339467945] [gazebo_ros2_control]: found initial value: 0.000000 [gzserver-3] [INFO] [1685503634.339480145] [gazebo_ros2_control]: velocity [gzserver-3] [INFO] [1685503634.339490045] [gazebo_ros2_control]: Command: [gzserver-3] [INFO] [1685503634.339500045] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339518345] [gazebo_ros2_control]: Loading joint: joint_3 [gzserver-3] [INFO] [1685503634.339529145] [gazebo_ros2_control]: State: [gzserver-3] [INFO] [1685503634.339539545] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339549045] [gazebo_ros2_control]: found initial value: 0.000000 [gzserver-3] [INFO] [1685503634.339560345] [gazebo_ros2_control]: velocity [gzserver-3] [INFO] [1685503634.339570345] [gazebo_ros2_control]: Command: [gzserver-3] [INFO] [1685503634.339580945] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339596745] [gazebo_ros2_control]: Loading joint: joint_4 [gzserver-3] [INFO] [1685503634.339607345] [gazebo_ros2_control]: State: [gzserver-3] [INFO] [1685503634.339617045] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339625945] [gazebo_ros2_control]: found initial value: 0.000000 [gzserver-3] [INFO] [1685503634.339637045] [gazebo_ros2_control]: velocity [gzserver-3] [INFO] [1685503634.339646245] [gazebo_ros2_control]: Command: [gzserver-3] [INFO] [1685503634.339656045] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339673545] [gazebo_ros2_control]: Loading joint: joint_5 [gzserver-3] [INFO] [1685503634.339681245] [gazebo_ros2_control]: State: [gzserver-3] [INFO] [1685503634.339687245] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339693645] [gazebo_ros2_control]: found initial value: 0.000000 [gzserver-3] [INFO] [1685503634.339701245] [gazebo_ros2_control]: velocity [gzserver-3] [INFO] [1685503634.339707145] [gazebo_ros2_control]: Command: [gzserver-3] [INFO] [1685503634.339713145] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339722645] [gazebo_ros2_control]: Loading joint: joint_6 [gzserver-3] [INFO] [1685503634.339729245] [gazebo_ros2_control]: State: [gzserver-3] [INFO] [1685503634.339735045] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339740545] [gazebo_ros2_control]: found initial value: 0.000000 [gzserver-3] [INFO] [1685503634.339747545] [gazebo_ros2_control]: velocity [gzserver-3] [INFO] [1685503634.339753445] [gazebo_ros2_control]: Command: [gzserver-3] [INFO] [1685503634.339759445] [gazebo_ros2_control]: position [gzserver-3] [INFO] [1685503634.339879245] [resource_manager]: Initialize hardware 'GazeboSystem' [gzserver-3] [INFO] [1685503634.340063045] [resource_manager]: Successful initialization of hardware 'GazeboSystem' [gzserver-3] [INFO] [1685503634.340181345] [resource_manager]: 'configure' hardware 'GazeboSystem' [gzserver-3] [INFO] [1685503634.340187145] [resource_manager]: Successful 'configure' of hardware 'GazeboSystem' [gzserver-3] [INFO] [1685503634.340192045] [resource_manager]: 'activate' hardware 'GazeboSystem' [gzserver-3] [INFO] [1685503634.340195145] [resource_manager]: Successful 'activate' of hardware 'GazeboSystem' [gzserver-3] [INFO] [1685503634.340283245] [gazebo_ros2_control]: Loading controller_manager [gzserver-3] [INFO] [1685503634.357185244] [gazebo_ros2_control]: Loaded gazebo_ros2_control. [INFO] [spawn_entity-5]: process has finished cleanly [pid 1788] [INFO] [ros2-6]: process started with pid [1934] [INFO] [ros2-7]: process started with pid [1936] [gzserver-3] [INFO] [1685503635.299160028] [controller_manager]: Loading controller 'joint_state_broadcaster' [gzserver-3] [INFO] [1685503635.312398828] [controller_manager]: Setting use_sim_time=True for joint_state_broadcaster to match controller manager (see ros2_control#325 for details) [gzserver-3] [INFO] [1685503635.315865028] [controller_manager]: Configuring controller 'joint_state_broadcaster' [gzserver-3] [INFO] [1685503635.316443328] [joint_state_broadcaster]: 'joints' or 'interfaces' parameter is empty. All available state interfaces will be published [gzserver-3] [INFO] [1685503639.271185105] [controller_manager]: Loading controller 'arm_controller' [ros2-7] Sucessfully loaded controller joint_state_broadcaster into state active [gzserver-3] [INFO] [1685503639.293424404] [controller_manager]: Setting use_sim_time=True for arm_controller to match controller manager (see ros2_control#325 for details) [gzserver-3] [INFO] [1685503639.296883904] [controller_manager]: Configuring controller 'arm_controller' [gzserver-3] [INFO] [1685503639.297277404] [arm_controller]: No specific joint names are used for command interfaces. Using 'joints' parameter. [gzserver-3] [INFO] [1685503639.297381904] [arm_controller]: Command interfaces are [position] and state interfaces are [position velocity]. [gzserver-3] [INFO] [1685503639.297455104] [arm_controller]: Using 'splines' interpolation method. [gzserver-3] [INFO] [1685503639.299070304] [arm_controller]: Controller state will be published at 50.00 Hz. [gzserver-3] [INFO] [1685503639.300950304] [arm_controller]: Action status changes will be monitored at 20.00 Hz. [ros2-6] Sucessfully loaded controller arm_controller into state active [INFO] [ros2-7]: process has finished cleanly [pid 1936] [INFO] [ros2-6]: process has finished cleanly [pid 1934] [INFO] [gzclient-4]: process has finished cleanly [pid 1786]

Originally posted by Roskuttan on ROS Answers with karma: 53 on 2023-05-31

Post score: 2

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Comment by Gio on 2023-05-31:
I'm also having such issues in my project someone help me with a solution it's so urgent I'm at the deadline of my project

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Assuming this is Gazebo Classic (as opposed to the new Gazebo, formerly Ignition) I suspect this is the same as https://github.com/UniversalRobots/Universal_Robots_ROS2_Gazebo_Simulation/issues/19

There's a lot of detail there but I'll briefly summarize for the forum here.

In ROS 1, gazebo_ros_control set the Open Dynamics Engine dParamFmax parameter here. This parameter is used in ODE joint motors:

http://ode.org/wiki/index.php/Manual#Stops_and_motor_parameters

Joint motors solve all these problems: they bring the body up to speed in one time step, provided that does not take more force than is allowed

The gazebo_ros2_control plugin, as far as I can tell, does not set this parameter right now and IIRC it defaults to zero.

Because of the way passive joint friction is implemented in ODE, a joint motor with zero speed and a max force, a workaround for active joints without building gazebo_ros2_control from source is to add a joint <dynamics> tag to your URDF with the friction parameter set to some suitable value for this maximum joint motor force parameter.

gazebo_ros_control set the dParamFmax or fmax parameter to the joint effort limit. IMO, theoretically, it should probably be higher than that with joint effort limits enforced in some other way, but practically either should work fine for simulation.

Originally posted by danzimmerman with karma: 337 on 2023-05-31

This answer was ACCEPTED on the original site

Post score: 2

Original comments

Comment by Roskuttan on 2023-05-31:
I would like to extend my deepest gratitude for the outstanding solution you provided to our problem. The inclusion of the dynamics tag, incorporating friction and damping, in my code has had a remarkable impact. The manipulator now remains stationary as intended, which is exactly the behavior I had anticipated. Your willingness to address my inquiries has been incredibly beneficial. Your contribution, particularly the integration of the dynamics tag, has made a significant and valuable difference. I cannot express enough how grateful I am for your assistance.

Comment by Aki1608 on 2023-06-06:
This solved my issue as well. Thank you so much. @danzimmerman and @Roskuttan. :)

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