Increased the torque of the wheel joints to 1N each.

urdf/include/wheel.xacro

@@ -35,7 +35,7 @@
       <parent link="${parent}"/>
       <child link="${name}_wheel"/>
       <axis xyz="0 0 ${direction}"/>
-      <limit effort="0.1" velocity="20.0" upper="1e16" lower="-1e16"/>
+      <limit effort="1.0" velocity="20.0" upper="1e16" lower="-1e16"/>
       <!-- the limits only apply to revolute and prismatic joints -->
       <dynamics damping="0.001"/>
     </joint>