add transmission to the wheels:xacro.

Author: pxalcantara

urdf/include/common_macros.urdf.xacro

@@ -65,6 +65,18 @@
       <child link="${prefix}_wheel"/>
       <origin xyz="${pos_x_joint} ${reflect* pos_y_joint} ${pos_z_joint}" rpy="0 0 0"/>
     </joint>
+
+    <transmission name="${prefix}_wheel_transmission">
+      <type>transmission_interface/SimpleTransmission</type>
+      <joint name="${prefix}_wheel_joint">
+        <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
+      </joint>
+      <actuator name="${prefix}_motor">
+        <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
+        <mechanicalReduction>1</mechanicalReduction>
+      </actuator>
+    </transmission>
+    
   </xacro:macro>
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