Update Simulation/launch/turtlebot3_stage_1.launch,...

Update Simulation/launch/turtlebot3_stage_1.launch, Simulation/launch/turtlebot3_stage_2.launch, Simulation/launch/turtlebot3_stage_3.launch, Simulation/launch/turtlebot3_stage_4.launch, Simulation/launch/zylinder.launch files

Simulation/launch/turtlebot3_stage_1.launch

+<launch>
+  <arg name="model" default="$(env TURTLEBOT3_MODEL)" doc="model type [burger, waffle, waffle_pi]"/>
+  <arg name="x_pos" default="0.0"/>
+  <arg name="y_pos" default="0.0"/>
+  <arg name="z_pos" default="0.0"/>
+
+  <include file="$(find gazebo_ros)/launch/empty_world.launch">
+    <arg name="world_name" value="$(find turtlebot3_gazebo)/worlds/turtlebot3_stage_1.world"/>
+    <arg name="paused" value="false"/>
+    <arg name="use_sim_time" value="0.1"/>
+    <arg name="gui" value="true"/>
+    <arg name="headless" value="false"/>
+    <arg name="debug" value="false"/>
+  </include>  
+
+
+  <param name="robot_description" command="$(find xacro)/xacro.py $(find turtlebot3_description)/urdf/turtlebot3_$(arg model).urdf.xacro" />
+
+  <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-urdf -model turtlebot3_burger -x $(arg x_pos) -y $(arg y_pos) -z $(arg z_pos) -param robot_description" />
+
+</launch>

Simulation/launch/turtlebot3_stage_2.launch

+<launch>
+  <arg name="model" default="$(env TURTLEBOT3_MODEL)" doc="model type [burger, waffle, waffle_pi]"/>
+  <arg name="x_pos" default="0.0"/>
+  <arg name="y_pos" default="0.0"/>
+  <arg name="z_pos" default="0.0"/>
+
+  <include file="$(find gazebo_ros)/launch/empty_world.launch">
+    <arg name="world_name" value="$(find turtlebot3_gazebo)/worlds/turtlebot3_stage_2.world"/>
+    <arg name="paused" value="false"/>
+    <arg name="use_sim_time" value="true"/>
+    <arg name="gui" value="true"/>
+    <arg name="headless" value="false"/>
+    <arg name="debug" value="false"/>
+  </include>  
+
+
+  <param name="robot_description" command="$(find xacro)/xacro.py $(find turtlebot3_description)/urdf/turtlebot3_$(arg model).urdf.xacro" />
+
+  <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-urdf -model turtlebot3_burger -x $(arg x_pos) -y $(arg y_pos) -z $(arg z_pos) -param robot_description" />
+</launch>

Simulation/launch/turtlebot3_stage_3.launch

+<launch>
+  <arg name="model" default="$(env TURTLEBOT3_MODEL)" doc="model type [burger, waffle, waffle_pi]"/>
+  <arg name="x_pos" default="0.0"/>
+  <arg name="y_pos" default="0.0"/>
+  <arg name="z_pos" default="0.0"/>
+
+  <include file="$(find gazebo_ros)/launch/empty_world.launch">
+    <arg name="world_name" value="$(find turtlebot3_gazebo)/worlds/turtlebot3_stage_3.world"/>
+    <arg name="paused" value="false"/>
+    <arg name="use_sim_time" value="true"/>
+    <arg name="gui" value="true"/>
+    <arg name="headless" value="false"/>
+    <arg name="debug" value="false"/>
+  </include>  
+
+  <param name="robot_description" command="$(find xacro)/xacro.py $(find turtlebot3_description)/urdf/turtlebot3_$(arg model).urdf.xacro" />
+
+  <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-urdf -model turtlebot3_burger -x $(arg x_pos) -y $(arg y_pos) -z $(arg z_pos) -param robot_description" />
+
+</launch>

Simulation/launch/turtlebot3_stage_4.launch

+<launch>
+  <arg name="model" default="$(env TURTLEBOT3_MODEL)" doc="model type [burger, waffle, waffle_pi]"/>
+  <arg name="x_pos" default="-0.7"/>
+  <arg name="y_pos" default="0.0"/>
+  <arg name="z_pos" default="0.0"/>
+
+  <include file="$(find gazebo_ros)/launch/empty_world.launch">
+    <arg name="world_name" value="$(find turtlebot3_gazebo)/worlds/turtlebot3_stage_4.world"/>
+    <arg name="paused" value="false"/>
+    <arg name="use_sim_time" value="true"/>
+    <arg name="gui" value="true"/>
+    <arg name="headless" value="false"/>
+    <arg name="debug" value="false"/>
+  </include>  
+
+
+  <param name="robot_description" command="$(find xacro)/xacro.py $(find turtlebot3_description)/urdf/turtlebot3_$(arg model).urdf.xacro" />
+
+  <node name="spawn_urdf" pkg="gazebo_ros" type="spawn_model" args="-urdf -model turtlebot3_burger -x $(arg x_pos) -y $(arg y_pos) -z $(arg z_pos) -param robot_description" />
+
+</launch>

Simulation/launch/zylinder.launch

+<launch>
+  <arg name="model" default="$(env TURTLEBOT3_MODEL)" doc="model type [burger, waffle, waffle_pi]"/>
+  <arg name="x_pos" default="-1.035058"/>
+  <arg name="y_pos" default="-1.035058"/>
+  <arg name="z_pos" default="-0.001001"/>
+
+  <include file="$(find gazebo_ros)/launch/empty_world.launch">
+    <arg name="world_name" value="$(find turtlebot3_gazebo)/worlds/zylinder.world"/>
+    <arg name="paused" value="false"/>
+    <arg name="use_sim_time" value="true"/>
+    <arg name="gui" value="true"/>
+    <arg name="headless" value="false"/>
+    <arg name="debug" value="false"/>
+  </include>
+
+  <param name="robot_description" command="$(find xacro)/xacro --inorder $(find turtlebot3_description)/urdf/turtlebot3_$(arg model).urdf.xacro" />
+
+  <node pkg="gazebo_ros" type="spawn_model" name="spawn_urdf" args="-urdf -model turtlebot3_$(arg model) -x $(arg x_pos) -y $(arg y_pos) -z $(arg z_pos) -param robot_description" />
+</launch>