QCAR cannot be generated correctly in gazebo using the launch file

[LinTianlang]

Problem description

The QCAR I generated in gazebo with the original launch file was overturned, but after I changed the z-axis of the generate parameter in the file from -0.1 to +0.1, it could be generated normally.

when z-axis param is -0.1

when z-axis param is 0.1

The modified part of the launch file

<!-- Set initial robot pose -->
<arg name="x" default="0.5"/>
<arg name="y" default="-0.4"/>
<arg name="z" default="0.1"/>
<arg name="roll" default="0"/>
<arg name="pitch" default="0"/>
<arg name="yaw" default="0.5"/>

[LinTianlang]

My environment is Ubuntu 20.04 with ros noetic.