diff --git a/nav2_minimal_tb3_sim/urdf/gz_waffle_gps.sdf.xacro b/nav2_minimal_tb3_sim/urdf/gz_waffle_gps.sdf.xacro
index 4272066..9e07859 100644
--- a/nav2_minimal_tb3_sim/urdf/gz_waffle_gps.sdf.xacro
+++ b/nav2_minimal_tb3_sim/urdf/gz_waffle_gps.sdf.xacro
@@ -156,7 +156,7 @@
             </mesh>
           </geometry>
           <material>
-            <diffuse>1 1 1</diffuse>
+            <diffuse>0.5 0.5 0.5</diffuse>
           </material>
         </visual>
 
@@ -215,23 +215,23 @@
           </geometry>
           <surface>
             <friction>
-              <ode>
+              <bullet>
                 <mu>1</mu>
                 <mu2>1</mu2>
                 <slip1>0.035</slip1>
                 <slip2>0</slip2>
                 <fdir1>0 0 1</fdir1>
-              </ode>
+              </bullet>
             </friction>
             <contact>
-              <ode>
+              <bullet>
                 <soft_cfm>0</soft_cfm>
                 <soft_erp>0.2</soft_erp>
                 <kp>1e+5</kp>
                 <kd>1</kd>
                 <max_vel>0.01</max_vel>
                 <min_depth>0.001</min_depth>
-              </ode>
+              </bullet>
             </contact>
           </surface>
         </collision>
@@ -245,7 +245,7 @@
             </mesh>
           </geometry>
           <material>
-            <diffuse>1 1 1</diffuse>
+            <diffuse>0.5 0.5 0.5</diffuse>
           </material>
         </visual>
       </link>
@@ -275,23 +275,23 @@
           </geometry>
           <surface>
             <friction>
-              <ode>
+              <bullet>
                 <mu>1</mu>
                 <mu2>1</mu2>
                 <slip1>0.035</slip1>
                 <slip2>0</slip2>
                 <fdir1>0 0 1</fdir1>
-              </ode>
+              </bullet>
             </friction>
             <contact>
-              <ode>
+              <bullet>
                 <soft_cfm>0</soft_cfm>
                 <soft_erp>0.2</soft_erp>
                 <kp>1e+5</kp>
                 <kd>1</kd>
                 <max_vel>0.01</max_vel>
                 <min_depth>0.001</min_depth>
-              </ode>
+              </bullet>
             </contact>
           </surface>
         </collision>
@@ -305,13 +305,13 @@
             </mesh>
           </geometry>
           <material>
-            <diffuse>1 1 1</diffuse>
+            <diffuse>0.5 0.5 0.5</diffuse>
           </material>
         </visual>
       </link>
 
       <link name='caster_back_right_link'>
-        <pose>-0.177 -0.064 -0.004 0 0 0</pose>
+        <pose>-0.177 -0.064 -0.004 -1.57 0 0</pose>
         <inertial>
           <mass>0.001</mass>
           <inertia>
@@ -323,29 +323,41 @@
             <izz>0.00001</izz>
           </inertia>
         </inertial>
-        <collision name='collision'>
+        <collision name='caster_back_right_collision'>
           <geometry>
             <sphere>
-              <radius>0.005000</radius>
+              <radius>0.0060000</radius>
             </sphere>
           </geometry>
           <surface>
             <contact>
-              <ode>
+              <bullet>
                 <soft_cfm>0</soft_cfm>
                 <soft_erp>0.2</soft_erp>
                 <kp>1e+5</kp>
                 <kd>1</kd>
                 <max_vel>0.01</max_vel>
                 <min_depth>0.001</min_depth>
-              </ode>
+              </bullet>
             </contact>
           </surface>
         </collision>
+
+        <visual name="sphere_visual">
+          <geometry>
+            <sphere>
+              <radius>0.0060000</radius>
+            </sphere>
+          </geometry>
+          <material>
+            <diffuse>0.5 0.5 0.5</diffuse>
+          </material>
+        </visual>
       </link>
 
       <link name='caster_back_left_link'>
-        <pose>-0.177 0.064 -0.004 0 0 0</pose>
+        <pose>-0.177 0.064 -0.004 -1.57 0 0</pose>
+
         <inertial>
           <mass>0.001</mass>
           <inertia>
@@ -357,25 +369,35 @@
             <izz>0.00001</izz>
           </inertia>
         </inertial>
-        <collision name='collision'>
+        <collision name='caster_back_left_collision'>
           <geometry>
             <sphere>
-              <radius>0.005000</radius>
+              <radius>0.0060000</radius>
             </sphere>
           </geometry>
           <surface>
             <contact>
-              <ode>
+              <bullet>
                 <soft_cfm>0</soft_cfm>
                 <soft_erp>0.2</soft_erp>
                 <kp>1e+5</kp>
                 <kd>1</kd>
                 <max_vel>0.01</max_vel>
                 <min_depth>0.001</min_depth>
-              </ode>
+              </bullet>
             </contact>
           </surface>
         </collision>
+       <visual name="sphere_visual">
+          <geometry>
+            <sphere>
+              <radius>0.0060000</radius>
+            </sphere>
+          </geometry>
+          <material>
+            <diffuse>0.5 0.5 0.5</diffuse>
+          </material>
+        </visual>
       </link>
 
       <link name="camera_link">