Trouble with crazyflie2 hovering example. [Ubuntu 18.04, ROS Melodic, Gazebo 9]

[umidah]

Good day, I installed CrazyS for ubuntu 18.04, ROS melodic and Gazebo9. When running the crazyflie2 hovering example, I could not get it to run.

I used the example command given in the readme:

roslaunch rotors_gazebo crazyflie2_hovering_example.launch

This was the error displayed for me.

... logging to /home/ajtpa/.ros/log/cdbdd2ee-835f-11ec-989a-e0d55ea1eb65/roslaunch-otonokizaka-11207.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.

xacro: in-order processing became default in ROS Melodic. You can drop the option.
name 'namespace' is not defined 
when evaluating expression 'namespace'
when processing file: /home/ajtpa/catkin_ws/src/CrazyS/rotors_description/urdf/component_snippets.xacro
included from: /home/ajtpa/catkin_ws/src/CrazyS/rotors_description/urdf/crazyflie2_base.xacro
included from: /home/ajtpa/catkin_ws/src/CrazyS/rotors_description/urdf/mav_generic_odometry_sensor.gazebo
RLException: while processing /home/ajtpa/catkin_ws/src/CrazyS/rotors_gazebo/launch/spawn_mav_crazyflie.launch:
Invalid <param> tag: Cannot load command parameter [robot_description]: command [['/opt/ros/melodic/lib/xacro/xacro', '--inorder', '/home/ajtpa/catkin_ws/src/CrazyS/rotors_description/urdf/mav_generic_odometry_sensor.gazebo', 'enable_logging:=false', 

If any more information is needed, I would gladly provide it.

EDIT: This was done in a fresh install of Ubuntu 18.04

[welcome]

Thanks for opening your first issue here! Make sure that no other issues on the same topic have already been opened!

[dingthe4th]

Hello, I got the same issue that returns the same error message. I followed the instruction in the README.md for Ubuntu 18.04.

[gsilano]

It seems that the problem lies in some hold definitions contained in the spawn_mav_crazyflie.launch. Open the file, and add the --inorder option as described in here https://answers.ros.org/question/354092/xacro-in-order-processing-for-husky_gazebo/. I hope this helps.

Xacro in-order processing for husky_gazebo - ROS Answers: Open Source Q&A Forum

After trying to run the following command roslaunch husky_gazebo husky_playpen.launch from this tutorial: http://wiki.ros.org/husky_navigation/... I encounter the following error: ... logging to /home/daniel/.ros/log/2e76d420-a6c4-11ea-afba-2390d77f85eb/roslaunch-daniel-Inspiron-7559-14421.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. xacro: in-order processing became default in ROS Melodic. You can drop the option. 'bool' object has no attribute 'lower' when evaluating expression 'topbar_needed_kinect.lower() == 'true' or topbar_needed_kinect == '1' or topbar_needed_realsense == 'true' or topbar_needed_realsense == '1'' when processing file: /home/daniel/husky_ws/src/husky_description/urdf/husky.urdf.xacro RLException: while processing /home/daniel/husky_ws/src/husky_gazebo/launch/spawn_husky.launch: while processing /home/daniel/husky_ws/src/husky_control/launch/control.launch: while processing /home/daniel/husky_ws/src/husky_description/launch/description.launch: Invalid tag: Cannot load command parameter [robot_description]: command [['/opt/ros/noetic/lib/xacro/xacro', '/home/daniel/husky_ws/src/husky_description/urdf/husky.urdf.xacro', '--inorder', 'robot_namespace:=/', 'laser_enabled:=true', 'kinect_enabled:=false', 'realsense_enabled:=false', 'urdf_extras:=']] returned with code [2]. Param xml is The traceback for the exception was written to the log file

[umidah]

Thanks for the reply, I'll check it out. If it does not work, I might try re-installing with ubuntu 20.04 and ROS noetic.

[dingthe4th]

Thanks for the quick reply. Unfortunately, the --inorder argument is already in the file as seen below.

If I try to launch the file with or without the --inorder, the same error appears.

[gsilano]

Looking at your screens, especially the second, it seems there is a problem with the namespace. Could you try to run any other launch file in the repository? I would like to understand if this problem affects only the file you mentioned or all the scripts have suffer of the same issue. Thanks!

[dingthe4th]

I tried it with:
mav_with_keyboard.launch and crazyflie2_swarm_hovering_example.launch, which also suffers from the issue.

[gsilano]

Have you checked if the repository source is working correctly? I mean, run the following commands roscd rotors_control and roscd rotors_gazebo.

[dingthe4th]

I am not sure if I follow but when I run the commands it shows the following:

I followed the Installation Instructions - Ubuntu 18.04 with ROS Melodic and Gazebo 9.

[gsilano]

Ok, so everything seems to be right with the ROS environment. Have you tried to run the Crazyflie example without the controller?

[dingthe4th]

If I try to run the file and comment the controller part, this is the result:

[gsilano]

Ok! Let me test it on my PC. I wil give you back in a short time.

[dingthe4th]

Good day sir, are there updates to a fix to this issue? Thanks!

[dingthe4th]

I tried reinstalling it again in a fresh machine, and the error is still there. Problem regarding namespace.

[dingthe4th]

I tried installing it with Ubuntu 20.04 and it works with no issues, I guess there's a problem within Ubuntu 18.04. Thanks for your time.

[gsilano]

Ok great! Did you compare the launch files? I'm curious if the problem lies there, or is it just a problem with ROS. However, this incompatibility problem is new to me.

[dingthe4th]

Unfortunately no as I have already deleted my Ubuntu 18.04 to install the new version.

[gsilano]

Ah, okay. Finally you managed to make it works, and this what really matters ;-) Enjoy!

[anavsalkar]

Hello, I am facing the same issue on my 20.04 system. I correctly installed as per the instructions for Ubuntu 20.04.

I tried changing the "<param name="robot_description"......" in the "spawn_mav.launch" file including/ommiting '--inorder' or 'xacro' or 'xacro.py' as suggested in ( https://answers.ros.org/question/122021/xacro-problem-invalid-param-tag-cannot-load-command-parameter-robot_description/ ), without any success.
What's surprising is that I had no trouble working with RotorS installation from 'eth-asl' when I last used it 2 months back. Now, both the installations (earlier RotorS from eth-asl and CrazyS) give the same errors. Don't know if some update has caused this.
Thank you in advance for any help!

xacro problem: Invalid tag: Cannot load command parameter [robot_description] - ROS Answers: Open Source Q&A Forum

Just like the topic I posed, when I try to use roslaunch command to run in the terminal, I met this problem (as followed): Invalid tag: Cannot load command parameter [robot_description]: command [/opt/ros/groovy/stacks/xacro/xacro.py '/home/viki/ros_workspace/smartcar_description/urdf/smartcar.urdf.xacro'] returned with code [1]. Param xml is I have no idea how to solve this problem, I sincerely you could give the instructions about how to solve this problem. Thanks so much for your time. when I run the code rosrun xacro xacro.py /home/viki/ros_workspace/smartcar_description/urdf/smartcar.urdf.xacro to check the xacro, there is the information showed as followed: Expat parsing error. Check that: - Your XML is correctly formed - You have the xacro xmlns declaration: xmlns:xacro="http://www.ros.org/wiki/xacro" Traceback (most recent call last): File "/opt/ros/groovy/stacks/xacro/xacro.py", line 35, in xacro.main() File "/opt/ros/groovy/stacks/xacro/src/xacro.py", line 542, in main doc = parse(f) File "/usr/lib/python2.7/xml/dom/minidom.py", line 1920, in parse return expatbuilder.parse(file) File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 928, in parse result = builder.parseFile(file) File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 207, in parseFile parser.Parse(buffer, 0) xml.parsers.expat.ExpatError: junk after document element: line 197, column 0 Can you give me some information about how to solve the problem? Thanks so much!

[anavsalkar]

I managed to solve the issue. Well, like I said it was indeed due to version updates. I removed xacro and xacro-1.14.11.egg-info directories from /opt/ros/noetic/lib/python3/dist-packages folder using sudo rm -r ... command and installed the 1.13.3 version of xacro using pip3 install xacro==1.13.3. This simple downgrading from 1.14.11 to 1.13.3 worked for me, without any changes in launch files.

[gsilano]

Great! Thanks for letting the community know about this. I'll add these instructions to the README.md file in case someone else experiences the problem.

[dogukanteber]

Thanks a lot @anavsalkar. You saved me from a headache. Your solution worked.