Error during mavros Multi-Vehicle Simulation with px4 in Gazebo | Invalid <param> tag

Question

I followed the instruction as mentioned here. Everything worked fine but at last stage when I try to run:-

roslaunch px4 multi_uav_mavros_sitl.launch

I get following:-

... logging to /home/yograj/.ros/log/40d4394e-0a3d-11e8-a1f1-3c77e68de09b/roslaunch-yograj-Inspiron-5537-12334.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

Usage: xacro.py [options] <input>

xacro.py: error: expected exactly one input file as argument
while processing /home/yograj/src/Firmware/launch/single_vehcile_spawn.launch:
Invalid <param> tag: Cannot load command parameter [iris_1_sdf]: command [/opt/ros/kinetic/share/xacro/xacro.py /home/yograj/src/Firmware/Tools/sitl_gazebo/models/rotors_description/urdf/iris_base.xacro rotors_description_dir:=/home/yograj/src/Firmware/Tools/sitl_gazebo/models/rotors_description mavlink_udp_port:=14560 > iris_1.urdf ; 'gz sdf -p iris_1.urdf'] returned with code [2]. 

Param xml is <param command="$(arg cmd)" name="$(arg vehicle)_$(arg ID)_sdf"/>
The traceback for the exception was written to the log file

Launch file

<launch>

    <!-- Posix SITL environment launch script -->
    <arg name="x" default="0"/>
    <arg name="y" default="0"/>
    <arg name="z" default="0"/>
    <arg name="R" default="0"/>
    <arg name="P" default="0"/>
    <arg name="Y" default="0"/>
    <arg name="est" default="ekf2"/>
    <arg name="vehicle" default="iris"/>
    <arg name="ID" default="1"/>
    <arg name="rcS" default="$(find px4)/posix-configs/SITL/init/$(arg est)/$(arg vehicle)_$(arg ID)"/>
    <arg name="mavlink_udp_port" default="14560" />


    <arg name="cmd" default="$(find xacro)/xacro.py $(find px4)/Tools/sitl_gazebo/models/rotors_description/urdf/$(arg vehicle)_base.xacro rotors_description_dir:=$(find px4)/Tools/sitl_gazebo/models/rotors_description mavlink_udp_port:=$(arg mavlink_udp_port) > $(arg vehicle)_$(arg ID).urdf ; 'gz sdf -p $(arg vehicle)_$(arg ID).urdf'" />


    <param command="$(arg cmd)" name="$(arg vehicle)_$(arg ID)_sdf" />

    <node name="sitl_$(arg ID)" pkg="px4" type="px4" output="screen"
        args="$(find px4) $(arg rcS)">
    </node>

    <node name="$(arg vehicle)_$(arg ID)_spawn" output="screen" pkg="gazebo_ros" type="spawn_model"
        args="-sdf -param $(arg vehicle)_$(arg ID)_sdf -model $(arg vehicle)_$(arg ID) -x $(arg x) -y $(arg y) -z $(arg z) -R $(arg R) -P $(arg P) -Y $(arg Y)" respawn="false"/>


</launch>

<!-- vim: set et ft=xml fenc=utf-8 ff=unix sts=0 sw=4 ts=4 : -->

Answer 1

If you are using old version of px4 firmware. There was some problem with launch file (single_vehcile_spawn.launch). Correcting

 <arg name="cmd" default="$(find xacro)/xacro.py $(find px4)/Tools/sitl_gazebo/models/rotors_description/urdf/$(arg vehicle)_base.xacro rotors_description_dir:=$(find px4)/Tools/sitl_gazebo/models/rotors_description mavlink_udp_port:=$(arg mavlink_udp_port) > $(arg vehicle)_$(arg ID).urdf ; 'gz sdf -p $(arg vehicle)_$(arg ID).urdf'" />

in single_vehcile_spawn.launch with

<arg name="cmd" default="$(find xacro)/xacro.py $(find px4)/Tools/sitl_gazebo/models/rotors_description/urdf/$(arg vehicle)_base.xacro rotors_description_dir:=$(find px4)/Tools/sitl_gazebo/models/rotors_description mavlink_udp_port:=$(arg mavlink_udp_port)" />