Issue with reading xacro file in UAV demo on ROS-Melodic

[danielvennestrom]

I had an issue where the UAV demo did not want to launch. It turned out that ROS-melodic had an error with xacro. The maintainer of the xacro package is aware of this and has triggered a release, but it is not yet synced.

As a fix I ended up changing to the the testing repository of ROS-Melodic. Here a newer version of xacro is available, which I simply downloaded/updated through "sudo apt-get ros-melodic-xacro".

The release that was triggered by the xacro maintainer has yet to be synced due to a lot of regression in melodic.

Please see the links for more context:
ethz-asl/rotors_simulator#695 (comment)
ros/xacro#316 (comment)
ros/rosdistro#32236
http://wiki.ros.org/TestingRepository

Error received:
RLException: while processing /home/daniel/gbplanner2_ws/src/sim/rotors_simulator/rotors_gazebo/launch/spawn_mav.launch: Invalid <param> tag: Cannot load command parameter [robot_description]: command [['/opt/ros/melodic/lib/xacro/xacro', '/home/daniel/gbplanner2_ws/src/sim/rotors_simulator/rotors_description/urdf/rmf_obelix.gazebo', 'enable_logging:=false', 'enable_ground_truth:=true', 'enable_mavlink_interface:=false', 'log_file:=rmf_obelix', 'wait_to_record_bag:=false', 'mav_name:=rmf_obelix', 'namespace:=rmf_obelix']] returned with code [2].

Param xml is <param command=" $(find xacro)/xacro '$(arg model)' enable_logging:=$(arg enable_logging) enable_ground_truth:=$(arg enable_ground_truth) enable_mavlink_interface:=$(arg enable_mavlink_interface) log_file:=$(arg log_file) wait_to_record_bag:=$(arg wait_to_record_bag) mav_name:=$(arg mav_name) namespace:=$(arg namespace)" name="robot_description"/>

[MihirDharmadhikari]

Hello,

Thank you for pointing this out. I will add a section about this in the Wiki - bug fixes.

Best,
Mihir