Hi,

I am learning how to use OpenAI-ROS package from here. I am trying to run the example of learning the object pushing task using fetch robot. For that I need to have the package fetch_simple_simulation which I have downloaded from here and the supporting package spawn_robot_tools from here. In order to check whether my simulator is running properly or not, I ran the following command

roslaunch fetch_simple_description main.launch By running the above command, I got error as No link elements found in urdf file. The complete output of the above roslaunch command is provided below. I am unable to fix the error and any help in resolving the issue will be appreciated.

I am using ROS Noetic, Ubuntu 20.04.

... logging to /home/user/.ros/log/7d7a5516-7ecc-11eb-a64c-eb44e79e9fe4/roslaunch-user-ai-15108.log
Checking log directory for disk usage. This may take a while.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

started roslaunch server http://user-ai:43231/

SUMMARY
========

PARAMETERS
 * /fetch/bellows_joint_position_controller/joint: bellows_joint
 * /fetch/bellows_joint_position_controller/pid/d: 1000.0
 * /fetch/bellows_joint_position_controller/pid/i: 0.0
 * /fetch/bellows_joint_position_controller/pid/p: 10000.0
 * /fetch/bellows_joint_position_controller/type: effort_controller...
 * /fetch/elbow_flex_joint_position_controller/joint: elbow_flex_joint
 * /fetch/elbow_flex_joint_position_controller/pid/d: 10.0
 * /fetch/elbow_flex_joint_position_controller/pid/i: 10.0
 * /fetch/elbow_flex_joint_position_controller/pid/p: 3000.0
 * /fetch/elbow_flex_joint_position_controller/type: effort_controller...
 * /fetch/forearm_roll_joint_position_controller/joint: forearm_roll_joint
 * /fetch/forearm_roll_joint_position_controller/pid/d: 0.0
 * /fetch/forearm_roll_joint_position_controller/pid/i: 0.1
 * /fetch/forearm_roll_joint_position_controller/pid/p: 3000.0
 * /fetch/forearm_roll_joint_position_controller/type: effort_controller...
 * /fetch/head_pan_joint_position_controller/joint: head_pan_joint
 * /fetch/head_pan_joint_position_controller/pid/d: 20.0
 * /fetch/head_pan_joint_position_controller/pid/i: 0.0
 * /fetch/head_pan_joint_position_controller/pid/p: 100.0
 * /fetch/head_pan_joint_position_controller/type: effort_controller...
 * /fetch/head_tilt_joint_position_controller/joint: head_tilt_joint
 * /fetch/head_tilt_joint_position_controller/pid/d: 1.0
 * /fetch/head_tilt_joint_position_controller/pid/i: 0.0
 * /fetch/head_tilt_joint_position_controller/pid/p: 10.0
 * /fetch/head_tilt_joint_position_controller/type: effort_controller...
 * /fetch/joint_state_controller/publish_rate: 50
 * /fetch/joint_state_controller/type: joint_state_contr...
 * /fetch/l_gripper_finger_joint_position_controller/joint: l_gripper_finger_...
 * /fetch/l_gripper_finger_joint_position_controller/pid/d: 0.0
 * /fetch/l_gripper_finger_joint_position_controller/pid/i: 0.1
 * /fetch/l_gripper_finger_joint_position_controller/pid/p: 5000.0
 * /fetch/l_gripper_finger_joint_position_controller/type: effort_controller...
 * /fetch/r_gripper_finger_joint_position_controller/joint: r_gripper_finger_...
 * /fetch/r_gripper_finger_joint_position_controller/pid/d: 0.0
 * /fetch/r_gripper_finger_joint_position_controller/pid/i: 0.1
 * /fetch/r_gripper_finger_joint_position_controller/pid/p: 5000.0
 * /fetch/r_gripper_finger_joint_position_controller/type: effort_controller...
 * /fetch/shoulder_lift_joint_position_controller/joint: shoulder_lift_joint
 * /fetch/shoulder_lift_joint_position_controller/pid/d: 0.0
 * /fetch/shoulder_lift_joint_position_controller/pid/i: 0.1
 * /fetch/shoulder_lift_joint_position_controller/pid/p: 5000.0
 * /fetch/shoulder_lift_joint_position_controller/type: effort_controller...
 * /fetch/shoulder_pan_joint_position_controller/joint: shoulder_pan_joint
 * /fetch/shoulder_pan_joint_position_controller/pid/d: 200.0
 * /fetch/shoulder_pan_joint_position_controller/pid/i: 10.0
 * /fetch/shoulder_pan_joint_position_controller/pid/p: 1000.0
 * /fetch/shoulder_pan_joint_position_controller/type: effort_controller...
 * /fetch/torso_lift_joint_position_controller/joint: torso_lift_joint
 * /fetch/torso_lift_joint_position_controller/pid/d: 1000.0
 * /fetch/torso_lift_joint_position_controller/pid/i: 0.0
 * /fetch/torso_lift_joint_position_controller/pid/p: 10000.0
 * /fetch/torso_lift_joint_position_controller/type: effort_controller...
 * /fetch/upperarm_roll_joint_position_controller/joint: upperarm_roll_joint
 * /fetch/upperarm_roll_joint_position_controller/pid/d: 0.0
 * /fetch/upperarm_roll_joint_position_controller/pid/i: 0.1
 * /fetch/upperarm_roll_joint_position_controller/pid/p: 3000.0
 * /fetch/upperarm_roll_joint_position_controller/type: effort_controller...
 * /fetch/wrist_flex_joint_position_controller/joint: wrist_flex_joint
 * /fetch/wrist_flex_joint_position_controller/pid/d: 500.0
 * /fetch/wrist_flex_joint_position_controller/pid/i: 10.0
 * /fetch/wrist_flex_joint_position_controller/pid/p: 1000.0
 * /fetch/wrist_flex_joint_position_controller/type: effort_controller...
 * /fetch/wrist_roll_joint_position_controller/joint: wrist_roll_joint
 * /fetch/wrist_roll_joint_position_controller/pid/d: 500.0
 * /fetch/wrist_roll_joint_position_controller/pid/i: 0.0
 * /fetch/wrist_roll_joint_position_controller/pid/p: 1000.0
 * /fetch/wrist_roll_joint_position_controller/type: effort_controller...
 * /fetch_robot_description: <?xml version="1....
 * /gazebo/enable_ros_network: True
 * /robot_description: <?xml version="1....
 * /robot_state_publisher_fetch/publish_frequency: 5.0
 * /rosdistro: noetic
 * /rosversion: 1.15.9
 * /use_sim_time: True

NODES
  /
    controller_spawner (controller_manager/spawner)
    gazebo (gazebo_ros/gzserver)
    gazebo_gui (gazebo_ros/gzclient)
    robot_state_publisher_fetch (robot_state_publisher/robot_state_publisher)
    urdf_spawner (gazebo_ros/spawn_model)
    world_frames_connection (tf/static_transform_publisher)

auto-starting new master
process[master]: started with pid [15120]
ROS_MASTER_URI=http://localhost:11311

setting /run_id to 7d7a5516-7ecc-11eb-a64c-eb44e79e9fe4
process[rosout-1]: started with pid [15130]
started core service [/rosout]
process[gazebo-2]: started with pid [15137]
process[gazebo_gui-3]: started with pid [15141]
process[urdf_spawner-4]: started with pid [15146]
process[robot_state_publisher_fetch-5]: started with pid [15148]
process[controller_spawner-6]: started with pid [15149]
process[world_frames_connection-7]: started with pid [15150]
[ERROR] [1615070231.746103523]: No link elements found in urdf file
[WARN] [1615070231.949699, 0.000000]: DEPRECATION warning: --shutdown-timeout has no effect.
[INFO] [1615070231.950255, 0.000000]: Controller Spawner: Waiting for service /fetch/controller_man/load_controller
[INFO] [1615070231.996115, 0.000000]: Loading model XML from ros parameter fetch_robot_description
[INFO] [1615070231.998945, 0.000000]: Waiting for service /gazebo/spawn_urdf_model
[robot_state_publisher_fetch-5] process has died [pid 15148, exit code 1, cmd /opt/ros/noetic/lib/robot_state_publisher/robot_state_publisher robot_description:=fetch_robot_description /joint_states:=/fetch/joint_states __name:=robot_state_publisher_fetch __log:=/home/user/.ros/log/7d7a5516-7ecc-11eb-a64c-eb44e79e9fe4/robot_state_publisher_fetch-5.log].
log file: /home/user/.ros/log/7d7a5516-7ecc-11eb-a64c-eb44e79e9fe4/robot_state_publisher_fetch-5*.log
[ INFO] [1615070232.105759143]: Finished loading Gazebo ROS API Plugin.
[ INFO] [1615070232.107050594]: waitForService: Service [/gazebo/set_physics_properties] has not been advertised, waiting...
[ INFO] [1615070232.181881268]: Finished loading Gazebo ROS API Plugin.
[ INFO] [1615070232.182713474]: waitForService: Service [/gazebo_gui/set_physics_properties] has not been advertised, waiting...
[ INFO] [1615070233.224636209]: waitForService: Service [/gazebo/set_physics_properties] is now available.
[ INFO] [1615070233.240845770]: Physics dynamic reconfigure ready.
[INFO] [1615070233.505608, 0.000000]: Calling service /gazebo/spawn_urdf_model
Error [parser_urdf.cc:3193] Unable to call parseURDF on robot model
Error [parser.cc:488] parse as old deprecated model file failed.
[WARN] [1615070262.043419, 0.000000]: Controller Spawner couldn't find the expected controller_manager ROS interface.
[controller_spawner-6] process has finished cleanly
log file: /home/user/.ros/log/7d7a5516-7ecc-11eb-a64c-eb44e79e9fe4/controller_spawner-6*.log