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What Is UADF

The Universal Aircraft Description Format (UADF), defined by Tobas, is a format that extends the Universal Robot Description Format (URDF), a general-purpose format for describing robots, with aircraft-specific elements.

What Is URDF

It is a format for describing any robot represented as a rigid-link system. In addition to the mass, collision, and visual information of each link in a robot, it also defines the joints that connect them. For details, see urdf | ROS.org.

Differences Between UADF and URDF

In addition to the URDF joint types, UADF adds the following aircraft-specific joint types.

thrust

A joint representing a propulsion unit consisting of a motor and propeller. It is based on URDF's continuous, but differs in the following ways.

  • axis: Rotation axis. Thrust is assumed to be generated along the axis direction.
  • direction: Rotation direction. Specify either cw or ccw for value.

Note

A thrust joint must be an end joint.

cs

A joint representing a control surface on a fixed-wing aircraft. It is based on URDF's revolute.

Note

A cs joint must be an end joint.

tilt

Represents the tilt joint of an active tilt-rotor. It is based on URDF's revolute.

Note

Exactly one thrust joint must be connected downstream of a tilt joint.

How to Create UADF

Here, we create a UADF for the DJI F450, a typical quadcopter used in the tutorial.

f450

URDF supports importing mesh files and texture files for visualization. Since those files are often distributed together with the URDF itself, it is convenient to create a dedicated ROS package for each robot. In this example, we create a package called tobas_f450_description directly under ~/colcon_ws/src/ and include all required files in it. The completed package is published at TobasFlightControl/tobas_f450_description.

ROS Package Structure and Required Files

tobas_f450_description has the following structure.

tobas_f450_description/
├── meshes
│   ├── frame.stl
│   ├── phantom3_0945_ccw.stl
│   ├── phantom3_0945_cw.stl
│   └── tobas_fc100.stl
├── urdf
│   └── f450.uadf
├── CMakeLists.txt
└── package.xml

package.xml is a file that describes the package overview and dependencies. Exactly one of these must be placed at the root of every ROS package. Since the package created here does not depend on any external packages, it contains only the minimum required elements such as the package name and license.

<package format="3">
    <name>tobas_f450_description</name>
    <version>0.0.0</version>
    <description>A UADF example for the DJI F450.</description>
    <maintainer email="m.dohi@tobas.jp">Masayoshi Dohi</maintainer>
    <license>MIT</license>
    <buildtool_depend>ament_cmake</buildtool_depend>
    <export>
        <build_type>ament_cmake</build_type>
    </export>
</package>

CMakeLists.txt is a file that describes the package build and installation procedures. Configure it to install meshes, the directory that stores mesh files, and urdf, the directory that stores the UADF.

cmake_minimum_required(VERSION 3.25)
project(tobas_f450_description)
find_package(ament_cmake REQUIRED)
install(DIRECTORY meshes urdf DESTINATION share/${PROJECT_NAME})
ament_package()

How to Write UADF

The UADF for the F450 created here consists of the following components.

  • An empty root link (required)
  • The main frame including the motors
  • A battery fixed to the main frame
  • An FMU fixed to the main frame
  • Four propellers

Each of these elements is described as a single rigid link, and the entire model forms one tree structure by connecting them with appropriate joints.

In this example, all links under the main frame are attached directly to the root link. The overall tree structure is as follows.

base_link
├──frame
├──battery
├──fmu
├──propeller_0
├──propeller_1
├──propeller_2
└──propeller_3

First, describe the URDF root element. The URDF root element must be robot, and the name attribute must be specified. All elements below are described inside this root element.

<robot name="f450">
</robot>

Describe an empty root link inside robot. The root link is a conceptual link with no size or mass, and every UADF must have exactly one root link.

  <!-- Base Link (Empty) -->
  <link name="base_link"/>

Fix the main frame to the root link. The mesh file for visual is specified using a path relative to the package. In this way, package://<package name> can be used to describe a path relative to a ROS package. The collision geometry of collision is approximated as a rectangular box because using a mesh file would make the simulation heavier. The mass properties of inertial are copied directly from values obtained from 3D CAD.

  <!-- Main Frame -->
  <joint name="frame_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <parent link="base_link"/>
    <child link="frame"/>
  </joint>
  <link name="frame">
    <inertial>
      <mass value="0.55346"/>
      <origin xyz="0 0 -0.004136" rpy="0 0 0"/>
      <inertia ixx="0.008128" ixy="0" ixz="0" iyy="0.008193" iyz="0" izz="0.01597"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/frame.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 -0.03" rpy="0 0 0"/>
      <geometry>
        <box size="0.35 0.35 0.06"/>
      </geometry>
    </collision>
  </link>

Add the battery and FMU in the same way as the main frame. Their moments of inertia are calculated assuming the mass is uniformly distributed in a rectangular box of the same size as collision. For the specific calculation method, see Inertia Moment.

  <!-- Battery -->
  <joint name="battery_joint" type="fixed">
    <origin xyz="0 0 -0.025" rpy="0 0 0"/>
    <parent link="base_link"/>
    <child link="battery"/>
  </joint>
  <link name="battery">
    <inertial>
      <mass value="0.376"/>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="9.024e-05" ixy="0" ixz="0" iyy="0.000770831" iyz="0" izz="0.000824975"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="0.155 0.048 0.024"/>
      </geometry>
      <material name="yellow">
        <color rgba="1 1 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="0.155 0.048 0.024"/>
      </geometry>
    </collision>
  </link>

  <!-- Flight Management Unit -->
  <joint name="fmu_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <parent link="base_link"/>
    <child link="fmu"/>
  </joint>
  <link name="fmu">
    <inertial>
      <mass value="0.16"/>
      <origin xyz="0 0 0.014" rpy="0 0 0"/>
      <inertia ixx="6.17067e-05" ixy="0" ixz="0" iyy="0.000118453" iyz="0" izz="0.000159253"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/tobas_fc100.stl" scale="1 1 1"/>
      </geometry>
      <material name="red">
        <color rgba="1 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.014" rpy="0 0 0"/>
      <geometry>
        <box size="0.09 0.062 0.028"/>
      </geometry>
    </collision>
  </link>

Add a propeller. Specify the UADF-specific thrust as the joint type, set axis to the +Z-axis direction of thrust (0 0 1), and set direction to counterclockwise (ccw). The mesh file for visual is specified using a path relative to the package. The collision geometry of collision is approximated as a cylinder. The moment of inertia of inertial is calculated assuming the mass is uniformly distributed in a cylinder of the same size as collision. For the specific calculation method, see Inertia Moment.

  <!-- Propeller (0) -->
  <joint name="propeller_0_joint" type="thrust">
    <origin xyz="0.159099 -0.159099 0.0247" rpy="0 0 -0.785398"/>
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="propeller_0"/>
    <direction value="ccw"/>
  </joint>
  <link name="propeller_0">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/phantom3_0945_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>

Add the other three propellers in the same way. Note that their joint origins, rotation directions, and mesh paths are different.

The final UADF is as follows.

<robot name="f450">

  <!-- Base Link (Empty) -->
  <link name="base_link"/>

  <!-- Main Frame -->
  <joint name="frame_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <parent link="base_link"/>
    <child link="frame"/>
  </joint>
  <link name="frame">
    <inertial>
      <mass value="0.55346"/>
      <origin xyz="0 0 -0.004136" rpy="0 0 0"/>
      <inertia ixx="0.008128" ixy="0" ixz="0" iyy="0.008193" iyz="0" izz="0.01597"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/frame.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 -0.03" rpy="0 0 0"/>
      <geometry>
        <box size="0.35 0.35 0.06"/>
      </geometry>
    </collision>
  </link>

  <!-- Battery -->
  <joint name="battery_joint" type="fixed">
    <origin xyz="0 0 -0.025" rpy="0 0 0"/>
    <parent link="base_link"/>
    <child link="battery"/>
  </joint>
  <link name="battery">
    <inertial>
      <mass value="0.376"/>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="9.024e-05" ixy="0" ixz="0" iyy="0.000770831" iyz="0" izz="0.000824975"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="0.155 0.048 0.024"/>
      </geometry>
      <material name="yellow">
        <color rgba="1 1 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="0.155 0.048 0.024"/>
      </geometry>
    </collision>
  </link>

  <!-- Flight Management Unit -->
  <joint name="fmu_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <parent link="base_link"/>
    <child link="fmu"/>
  </joint>
  <link name="fmu">
    <inertial>
      <mass value="0.16"/>
      <origin xyz="0 0 0.014" rpy="0 0 0"/>
      <inertia ixx="6.17067e-05" ixy="0" ixz="0" iyy="0.000118453" iyz="0" izz="0.000159253"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/tobas_fc100.stl" scale="1 1 1"/>
      </geometry>
      <material name="red">
        <color rgba="1 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.014" rpy="0 0 0"/>
      <geometry>
        <box size="0.09 0.062 0.028"/>
      </geometry>
    </collision>
  </link>

  <!-- Propeller (0) -->
  <joint name="propeller_0_joint" type="thrust">
    <origin xyz="0.159099 -0.159099 0.0247" rpy="0 0 -0.785398"/>
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="propeller_0"/>
    <direction value="ccw"/>
  </joint>
  <link name="propeller_0">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/phantom3_0945_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>

  <!-- Propeller (1) -->
  <joint name="propeller_1_joint" type="thrust">
    <origin xyz="-0.159099 0.159099 0.0247" rpy="0 0 2.35619"/>
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="propeller_1"/>
    <direction value="ccw"/>
  </joint>
  <link name="propeller_1">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/phantom3_0945_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>

  <!-- Propeller (2) -->
  <joint name="propeller_2_joint" type="thrust">
    <origin xyz="0.159099 0.159099 0.0247" rpy="0 0 0.785398"/>
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="propeller_2"/>
    <direction value="cw"/>
  </joint>
  <link name="propeller_2">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/phantom3_0945_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>

  <!-- Propeller (3) -->
  <joint name="propeller_3_joint" type="thrust">
    <origin xyz="-0.159099 -0.159099 0.0247" rpy="0 0 -2.35619"/>
    <axis xyz="0 0 1"/>
    <parent link="base_link"/>
    <child link="propeller_3"/>
    <direction value="cw"/>
  </joint>
  <link name="propeller_3">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://tobas_f450_description/meshes/phantom3_0945_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>

</robot>

UADF Creation Examples

Above, we created a UADF for a simple quadcopter, but UADF can also represent many other types of aircraft. Here are several other UADF examples.

Unlike the previous example, these use XML macros called XACRO and perform the following kinds of programming-like processing internally:

  • Include other files
  • Define constants
  • Perform simple numerical calculations
  • Encapsulate repeated processing as functions

Using XACRO makes XML shorter and easier to understand.

Non-Planar Octacopter (TOC8)

An octacopter with eight thrust joints. However, each propeller is arranged to point outward from a vertex of a cube.

toc8_pt001

Before XACRO expansion 
<robot xmlns:xacro="http://ros.org/wiki/xacro" name="toc8_pt001">

  <!-- Included URDF Files -->
  <xacro:include filename="$(find tobas_description)/urdf/components/common.xacro"/>
  <xacro:include filename="$(find tobas_description)/urdf/components/fmu/tobas_fc100.xacro"/>
  <xacro:include filename="$(find tobas_description)/urdf/components/battery/sigp_6s_1100mah_120c.xacro"/>
  <xacro:include filename="$(find tobas_description)/urdf/components/combo/mt3508_0945.uadf"/>

  <!-- Properties -->
  <xacro:property name="frame_width" value="0.5"/>
  <xacro:property name="motor_offset" value="0.1705"/>
  <xacro:property name="x" value="${motor_offset/sqrt3}"/>
  <xacro:property name="prop_pitch" value="0.95"/>

  <!-- Base Link -->
  <link name="base_link"/>

  <!-- Frame -->
  <joint name="frame_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <parent link="base_link"/>
    <child link="frame"/>
  </joint>
  <link name="frame">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://toc8_pt001_description/meshes/frame.stl" scale="1 1 1"/>
      </geometry>
      <xacro:insert_block name="black"/>
    </visual>
    <inertial>
      <mass value="0.875668"/>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="2.731e-2" ixy="-1.176e-5" ixz="2.301e-5" iyy="2.415e-2" iyz="-3.35e-7" izz="2.615e-2"/>
    </inertial>
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <box size="${frame_width} ${frame_width} ${frame_width}"/>
      </geometry>
    </collision>
  </link>

  <!-- Flight Controller -->
  <xacro:tobas_fc100 parent="base_link">
    <origin xyz="0 0 0.0425" rpy="0 0 0"/>
  </xacro:tobas_fc100>

  <!-- Battery -->
  <xacro:sigp_6s_1100mah_120c link_name="battery" parent="base_link">
    <origin xyz="0 0 -0.060" rpy="${pi/2} 0 0"/>
  </xacro:sigp_6s_1100mah_120c>

  <!-- Propulsion System -->
  <xacro:mt3508_0945 parent="base_link" index="0" direction="ccw">
    <origin xyz="${x} ${x} ${x}" rpy="0 ${prop_pitch} ${pi/4*1}"/>
  </xacro:mt3508_0945>
  <xacro:mt3508_0945 parent="base_link" index="1" direction="cw">
    <origin xyz="${-x} ${x} ${x}" rpy="0 ${prop_pitch} ${pi/4*3}"/>
  </xacro:mt3508_0945>
  <xacro:mt3508_0945 parent="base_link" index="2" direction="ccw">
    <origin xyz="${-x} ${-x} ${x}" rpy="0 ${prop_pitch} ${pi/4*5}"/>
  </xacro:mt3508_0945>
  <xacro:mt3508_0945 parent="base_link" index="3" direction="cw">
    <origin xyz="${x} ${-x} ${x}" rpy="0 ${prop_pitch} ${pi/4*7}"/>
  </xacro:mt3508_0945>
  <xacro:mt3508_0945 parent="base_link" index="4" direction="cw">
    <origin xyz="${x} ${x} ${-x}" rpy="0 ${pi-prop_pitch} ${pi/4*1}"/>
  </xacro:mt3508_0945>
  <xacro:mt3508_0945 parent="base_link" index="5" direction="ccw">
    <origin xyz="${-x} ${x} ${-x}" rpy="0 ${pi-prop_pitch} ${pi/4*3}"/>
  </xacro:mt3508_0945>
  <xacro:mt3508_0945 parent="base_link" index="6" direction="cw">
    <origin xyz="${-x} ${-x} ${-x}" rpy="0 ${pi-prop_pitch} ${pi/4*5}"/>
  </xacro:mt3508_0945>
  <xacro:mt3508_0945 parent="base_link" index="7" direction="ccw">
    <origin xyz="${x} ${-x} ${-x}" rpy="0 ${pi-prop_pitch} ${pi/4*7}"/>
  </xacro:mt3508_0945>

</robot>
After XACRO expansion 
<robot name="toc8_pt001">
  <material name="black">
    <texture/>
    <color rgba="0 0 0 1"/>
  </material>
  <material name="blue">
    <texture/>
    <color rgba="0 0 1 1"/>
  </material>
  <material name="orange">
    <texture/>
    <color rgba="1 0.423529 0.0392157 1"/>
  </material>
  <material name="red">
    <texture/>
    <color rgba="1 0 0 1"/>
  </material>
  <material name="white">
    <texture/>
    <color rgba="1 1 1 1"/>
  </material>
  <link name="base_link"/>
  <link name="battery">
    <inertial>
      <mass value="0.205"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="5.10621e-05" ixy="0" ixz="0" iyy="0.000131422" iyz="0" izz="0.000122214"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <box size="0.077 0.035 0.042"/>
      </geometry>
      <material name="blue">
        <texture/>
        <color rgba="0 0 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <box size="0.077 0.035 0.042"/>
      </geometry>
    </collision>
  </link>
  <link name="fmu">
    <inertial>
      <mass value="0.2"/>
      <origin xyz="0 0 0.014" rpy="0 -0 0"/>
      <inertia ixx="7.71333e-05" ixy="0" ixz="0" iyy="0.000148067" iyz="0" izz="0.000199067"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/tobas_fc100.stl" scale="1 1 1"/>
      </geometry>
      <material name="red">
        <texture/>
        <color rgba="1 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.014" rpy="0 -0 0"/>
      <geometry>
        <box size="0.09 0.062 0.028"/>
      </geometry>
    </collision>
  </link>
  <link name="frame">
    <inertial>
      <mass value="0.875668"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="0.02731" ixy="-1.176e-05" ixz="2.301e-05" iyy="0.02415" iyz="-3.35e-07" izz="0.02615"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/frame.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <box size="0.5 0.5 0.5"/>
      </geometry>
    </collision>
  </link>
  <link name="motor_0">
    <inertial>
      <mass value="0.086"/>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <inertia ixx="1.36095e-05" ixy="0" ixz="0" iyy="1.36095e-05" iyz="0" izz="1.8963e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/mt3508_580kv.stl" scale="1 1 1"/>
      </geometry>
      <material name="orange">
        <texture/>
        <color rgba="1 0.423529 0.0392157 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.021" length="0.024"/>
      </geometry>
    </collision>
  </link>
  <link name="motor_1">
    <inertial>
      <mass value="0.086"/>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <inertia ixx="1.36095e-05" ixy="0" ixz="0" iyy="1.36095e-05" iyz="0" izz="1.8963e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/mt3508_580kv.stl" scale="1 1 1"/>
      </geometry>
      <material name="orange">
        <texture/>
        <color rgba="1 0.423529 0.0392157 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.021" length="0.024"/>
      </geometry>
    </collision>
  </link>
  <link name="motor_2">
    <inertial>
      <mass value="0.086"/>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <inertia ixx="1.36095e-05" ixy="0" ixz="0" iyy="1.36095e-05" iyz="0" izz="1.8963e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/mt3508_580kv.stl" scale="1 1 1"/>
      </geometry>
      <material name="orange">
        <texture/>
        <color rgba="1 0.423529 0.0392157 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.021" length="0.024"/>
      </geometry>
    </collision>
  </link>
  <link name="motor_3">
    <inertial>
      <mass value="0.086"/>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <inertia ixx="1.36095e-05" ixy="0" ixz="0" iyy="1.36095e-05" iyz="0" izz="1.8963e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/mt3508_580kv.stl" scale="1 1 1"/>
      </geometry>
      <material name="orange">
        <texture/>
        <color rgba="1 0.423529 0.0392157 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.021" length="0.024"/>
      </geometry>
    </collision>
  </link>
  <link name="motor_4">
    <inertial>
      <mass value="0.086"/>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <inertia ixx="1.36095e-05" ixy="0" ixz="0" iyy="1.36095e-05" iyz="0" izz="1.8963e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/mt3508_580kv.stl" scale="1 1 1"/>
      </geometry>
      <material name="orange">
        <texture/>
        <color rgba="1 0.423529 0.0392157 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.021" length="0.024"/>
      </geometry>
    </collision>
  </link>
  <link name="motor_5">
    <inertial>
      <mass value="0.086"/>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <inertia ixx="1.36095e-05" ixy="0" ixz="0" iyy="1.36095e-05" iyz="0" izz="1.8963e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/mt3508_580kv.stl" scale="1 1 1"/>
      </geometry>
      <material name="orange">
        <texture/>
        <color rgba="1 0.423529 0.0392157 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.021" length="0.024"/>
      </geometry>
    </collision>
  </link>
  <link name="motor_6">
    <inertial>
      <mass value="0.086"/>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <inertia ixx="1.36095e-05" ixy="0" ixz="0" iyy="1.36095e-05" iyz="0" izz="1.8963e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/mt3508_580kv.stl" scale="1 1 1"/>
      </geometry>
      <material name="orange">
        <texture/>
        <color rgba="1 0.423529 0.0392157 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.021" length="0.024"/>
      </geometry>
    </collision>
  </link>
  <link name="motor_7">
    <inertial>
      <mass value="0.086"/>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <inertia ixx="1.36095e-05" ixy="0" ixz="0" iyy="1.36095e-05" iyz="0" izz="1.8963e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/mt3508_580kv.stl" scale="1 1 1"/>
      </geometry>
      <material name="orange">
        <texture/>
        <color rgba="1 0.423529 0.0392157 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.012" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.021" length="0.024"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_0">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/phantom3_0945_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_1">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/phantom3_0945_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_2">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/phantom3_0945_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_3">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/phantom3_0945_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_4">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/phantom3_0945_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_5">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/phantom3_0945_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_6">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/phantom3_0945_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_7">
    <inertial>
      <mass value="0.011"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="3.9732e-05" ixy="0" ixz="0" iyy="3.9732e-05" iyz="0" izz="7.92e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_toc8_pt001_config/meshes/phantom3_0945_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.12" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <joint name="battery_joint" type="fixed">
    <origin xyz="0 0 -0.06" rpy="1.5708 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="battery"/>
  </joint>
  <joint name="fmu_joint" type="fixed">
    <origin xyz="0 0 0.0425" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="fmu"/>
  </joint>
  <joint name="frame_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="frame"/>
  </joint>
  <joint name="motor_0_joint" type="fixed">
    <origin xyz="0.0984382 0.0984382 0.0984382" rpy="9.54319e-17 0.95 0.785398"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="motor_0"/>
  </joint>
  <joint name="motor_1_joint" type="fixed">
    <origin xyz="-0.0984382 0.0984382 0.0984382" rpy="0 0.95 2.35619"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="motor_1"/>
  </joint>
  <joint name="motor_2_joint" type="fixed">
    <origin xyz="-0.0984382 -0.0984382 0.0984382" rpy="9.54319e-17 0.95 -2.35619"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="motor_2"/>
  </joint>
  <joint name="motor_3_joint" type="fixed">
    <origin xyz="0.0984382 -0.0984382 0.0984382" rpy="9.54319e-17 0.95 -0.785398"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="motor_3"/>
  </joint>
  <joint name="motor_4_joint" type="fixed">
    <origin xyz="0.0984382 0.0984382 -0.0984382" rpy="3.14159 0.95 -2.35619"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="motor_4"/>
  </joint>
  <joint name="motor_5_joint" type="fixed">
    <origin xyz="-0.0984382 0.0984382 -0.0984382" rpy="3.14159 0.95 -0.785398"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="motor_5"/>
  </joint>
  <joint name="motor_6_joint" type="fixed">
    <origin xyz="-0.0984382 -0.0984382 -0.0984382" rpy="3.14159 0.95 0.785398"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="motor_6"/>
  </joint>
  <joint name="motor_7_joint" type="fixed">
    <origin xyz="0.0984382 -0.0984382 -0.0984382" rpy="3.14159 0.95 2.35619"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="motor_7"/>
  </joint>
  <joint name="propeller_0_joint" type="thrust">
    <origin xyz="0 0 0.029" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="motor_0"/>
    <child link="propeller_0"/>
    <direction value="ccw"/>
  </joint>
  <joint name="propeller_1_joint" type="thrust">
    <origin xyz="0 0 0.029" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="motor_1"/>
    <child link="propeller_1"/>
    <direction value="cw"/>
  </joint>
  <joint name="propeller_2_joint" type="thrust">
    <origin xyz="0 0 0.029" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="motor_2"/>
    <child link="propeller_2"/>
    <direction value="ccw"/>
  </joint>
  <joint name="propeller_3_joint" type="thrust">
    <origin xyz="0 0 0.029" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="motor_3"/>
    <child link="propeller_3"/>
    <direction value="cw"/>
  </joint>
  <joint name="propeller_4_joint" type="thrust">
    <origin xyz="0 0 0.029" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="motor_4"/>
    <child link="propeller_4"/>
    <direction value="cw"/>
  </joint>
  <joint name="propeller_5_joint" type="thrust">
    <origin xyz="0 0 0.029" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="motor_5"/>
    <child link="propeller_5"/>
    <direction value="ccw"/>
  </joint>
  <joint name="propeller_6_joint" type="thrust">
    <origin xyz="0 0 0.029" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="motor_6"/>
    <child link="propeller_6"/>
    <direction value="cw"/>
  </joint>
  <joint name="propeller_7_joint" type="thrust">
    <origin xyz="0 0 0.029" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="motor_7"/>
    <child link="propeller_7"/>
    <direction value="ccw"/>
  </joint>
</robot>


Active Tilt Hexacopter (Voliro Like)

A hexacopter with six pairs of thrust joints and tilt joints.

voliro_like_pt003

Before XACRO expansion 
<robot xmlns:xacro="http://ros.org/wiki/xacro" name="voliro_like_pt003">

  <!-- Included URDF Files -->
  <xacro:include filename="$(find tobas_description)/urdf/components/common.xacro"/>
  <xacro:include filename="$(find tobas_description)/urdf/components/fmu/tobas_fc100.xacro"/>
  <xacro:include filename="$(find tobas_description)/urdf/components/battery/hrb_6s_5000mah_50c.xacro"/>
  <xacro:include filename="$(find tobas_description)/urdf/components/landing_gear/zhizicathy_electric_150.xacro"/>
  <xacro:include filename="$(find voliro_like_pt003_description)/urdf/tmotor_1344.uadf"/>

  <!-- Properties -->
  <xacro:property name="arm_offset" value="0.330"/>

  <!-- Base Link -->
  <link name="base_link"/>

  <!-- Body -->
  <joint name="frame_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <parent link="base_link"/>
    <child link="body"/>
  </joint>
  <link name="body">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://voliro_like_pt003_description/meshes/body.stl" scale="1 1 1"/>
      </geometry>
      <xacro:insert_block name="white"/>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <geometry>
        <mesh filename="package://voliro_like_pt003_description/meshes/body.stl" scale="1 1 1"/>
      </geometry>
    </collision>
    <inertial>
      <mass value="0.575"/>
      <origin xyz="-0.011 0 0.021" rpy="0 0 0"/>
      <inertia ixx="6.800e-3" ixy="-1.818e-5" ixz="-1.767e-4" iyy="7.155e-3" iyz="-9.915e-7" izz="1.333e-2"/>
    </inertial>
  </link>

  <!-- Flight Controller -->
  <xacro:tobas_fc100 parent="base_link">
    <origin xyz="0 0 0.058" rpy="0 0 0"/>
  </xacro:tobas_fc100>

  <!-- Battery -->
  <xacro:hrb_6s_5000mah_50c link_name="battery" parent="base_link">
    <origin xyz="0 0 0.026" rpy="${pi/2} 0 0"/>
  </xacro:hrb_6s_5000mah_50c>

  <!-- Tilt Rotor -->
  <xacro:macro name="tilt_rotor" params="index direction yaw_deg">
    <joint name="arm_${index}_joint" type="tilt">
      <origin xyz="${arm_offset*cos(yaw_deg*deg2rad)} ${arm_offset*sin(yaw_deg*deg2rad)} 0.029" rpy="0 0 ${yaw_deg*deg2rad}"/>
      <axis xyz="1 0 0"/>
      <parent link="base_link"/>
      <child link="arm_${index}"/>

      <!-- 9imod BLS-HV25MG-270 @8.4V: https://ja.aliexpress.com/item/1005007702114246.html -->
      <limit lower="${-135*deg2rad}" upper="${135*deg2rad}" velocity="${60*deg2rad/0.04}" effort="${25*gravity/100}"/>
    </joint>

    <link name="arm_${index}">
      <visual>
        <origin xyz="0 0 0" rpy="0 0 ${pi}"/>
        <geometry>
          <mesh filename="package://voliro_like_pt003_description/meshes/arm.stl" scale="1 1 1"/>
        </geometry>
        <xacro:insert_block name="black"/>
      </visual>
      <collision>
        <origin xyz="0 0 0" rpy="0 0 ${pi}"/>
        <geometry>
          <mesh filename="package://voliro_like_pt003_description/meshes/arm.stl" scale="1 1 1"/>
        </geometry>
      </collision>
      <inertial>
        <mass value="0.224"/>
        <origin xyz="0.025 0 5.736e-3" rpy="0 0 ${pi}"/>
        <inertia ixx="8.806e-5" ixy="0" ixz="-8.840e-5" iyy="3.292e-4" iyz="0" izz="2.949e-4"/>
      </inertial>
    </link>

    <xacro:tmotor_1344 parent="arm_${index}" index="${index}" direction="${direction}">
      <origin xyz="0 0 0.034" rpy="0 0 0"/>
    </xacro:tmotor_1344>
  </xacro:macro>

  <xacro:tilt_rotor index="0" direction="ccw" yaw_deg="30"/>
  <xacro:tilt_rotor index="1" direction="cw" yaw_deg="90"/>
  <xacro:tilt_rotor index="2" direction="ccw" yaw_deg="150"/>
  <xacro:tilt_rotor index="3" direction="cw" yaw_deg="210"/>
  <xacro:tilt_rotor index="4" direction="ccw" yaw_deg="270"/>
  <xacro:tilt_rotor index="5" direction="cw" yaw_deg="330"/>

  <!-- Landing Gear -->
  <xacro:zhizicathy_electric_150 parent="base_link" distance="0.165" max_angle="${55*deg2rad}">
    <origin xyz="0 0 0" rpy="0 0 0"/>
  </xacro:zhizicathy_electric_150>

</robot>
After XACRO expansion 
<robot name="voliro_like_pt003">
  <material name="black">
    <texture/>
    <color rgba="0 0 0 1"/>
  </material>
  <material name="red">
    <texture/>
    <color rgba="1 0 0 1"/>
  </material>
  <material name="white">
    <texture/>
    <color rgba="1 1 1 1"/>
  </material>
  <material name="yellow">
    <texture/>
    <color rgba="1 1 0 1"/>
  </material>
  <link name="arm_0">
    <inertial>
      <mass value="0.224"/>
      <origin xyz="0.025 0 0.005736" rpy="0 -0 3.14159"/>
      <inertia ixx="8.806e-05" ixy="0" ixz="-8.84e-05" iyy="0.0003292" iyz="0" izz="0.0002949"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="arm_1">
    <inertial>
      <mass value="0.224"/>
      <origin xyz="0.025 0 0.005736" rpy="0 -0 3.14159"/>
      <inertia ixx="8.806e-05" ixy="0" ixz="-8.84e-05" iyy="0.0003292" iyz="0" izz="0.0002949"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="arm_2">
    <inertial>
      <mass value="0.224"/>
      <origin xyz="0.025 0 0.005736" rpy="0 -0 3.14159"/>
      <inertia ixx="8.806e-05" ixy="0" ixz="-8.84e-05" iyy="0.0003292" iyz="0" izz="0.0002949"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="arm_3">
    <inertial>
      <mass value="0.224"/>
      <origin xyz="0.025 0 0.005736" rpy="0 -0 3.14159"/>
      <inertia ixx="8.806e-05" ixy="0" ixz="-8.84e-05" iyy="0.0003292" iyz="0" izz="0.0002949"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="arm_4">
    <inertial>
      <mass value="0.224"/>
      <origin xyz="0.025 0 0.005736" rpy="0 -0 3.14159"/>
      <inertia ixx="8.806e-05" ixy="0" ixz="-8.84e-05" iyy="0.0003292" iyz="0" izz="0.0002949"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="arm_5">
    <inertial>
      <mass value="0.224"/>
      <origin xyz="0.025 0 0.005736" rpy="0 -0 3.14159"/>
      <inertia ixx="8.806e-05" ixy="0" ixz="-8.84e-05" iyy="0.0003292" iyz="0" izz="0.0002949"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 3.14159"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/arm.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="base_link"/>
  <link name="battery">
    <inertial>
      <mass value="0.725"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="0.0002784" ixy="0" ixz="0" iyy="0.00159071" iyz="0" izz="0.00159071"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <box size="0.155 0.048 0.048"/>
      </geometry>
      <material name="yellow">
        <texture/>
        <color rgba="1 1 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <box size="0.155 0.048 0.048"/>
      </geometry>
    </collision>
  </link>
  <link name="body">
    <inertial>
      <mass value="0.575"/>
      <origin xyz="-0.011 0 0.021" rpy="0 -0 0"/>
      <inertia ixx="0.0068" ixy="-1.818e-05" ixz="-0.0001767" iyy="0.007155" iyz="-9.915e-07" izz="0.01333"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/body.stl" scale="1 1 1"/>
      </geometry>
      <material name="white">
        <texture/>
        <color rgba="1 1 1 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/body.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="fmu">
    <inertial>
      <mass value="0.16"/>
      <origin xyz="0 0 0.014" rpy="0 -0 0"/>
      <inertia ixx="6.17067e-05" ixy="0" ixz="0" iyy="0.000118453" iyz="0" izz="0.000159253"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/tobas_fc100.stl" scale="1 1 1"/>
      </geometry>
      <material name="red">
        <texture/>
        <color rgba="1 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.014" rpy="0 -0 0"/>
      <geometry>
        <box size="0.09 0.062 0.028"/>
      </geometry>
    </collision>
  </link>
  <link name="lg_base_link">
    <inertial>
      <mass value="1e-06"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="1e-12" ixy="0" ixz="0" iyy="1e-12" iyz="0" izz="1e-12"/>
    </inertial>
  </link>
  <link name="lg_left_bottom">
    <inertial>
      <mass value="0.0706"/>
      <origin xyz="0 0.029 -0.142" rpy="0 -0 0"/>
      <inertia ixx="0.0002169" ixy="0" ixz="0" iyy="0.000432" iyz="4.968e-05" izz="0.0002437"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/bottom.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0.013 -0.085" rpy="0.261799 -0 0"/>
      <geometry>
        <cylinder radius="0.008" length="0.18"/>
      </geometry>
    </collision>
    <collision>
      <origin xyz="0 0.036 -0.17" rpy="0 -0 0"/>
      <geometry>
        <box size="0.24 0.02 0.02"/>
      </geometry>
    </collision>
  </link>
  <link name="lg_left_top">
    <inertial>
      <mass value="0.0988"/>
      <origin xyz="0 0.0175 -0.007" rpy="0 -0 0"/>
      <inertia ixx="3.841e-05" ixy="0" ixz="0" iyy="5.358e-06" iyz="8.642e-07" izz="4.031e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/top.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/top.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="lg_right_bottom">
    <inertial>
      <mass value="0.0706"/>
      <origin xyz="0 0.029 -0.142" rpy="0 -0 0"/>
      <inertia ixx="0.0002169" ixy="0" ixz="0" iyy="0.000432" iyz="4.968e-05" izz="0.0002437"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/bottom.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0.013 -0.085" rpy="0.261799 -0 0"/>
      <geometry>
        <cylinder radius="0.008" length="0.18"/>
      </geometry>
    </collision>
    <collision>
      <origin xyz="0 0.036 -0.17" rpy="0 -0 0"/>
      <geometry>
        <box size="0.24 0.02 0.02"/>
      </geometry>
    </collision>
  </link>
  <link name="lg_right_top">
    <inertial>
      <mass value="0.0988"/>
      <origin xyz="0 0.0175 -0.007" rpy="0 -0 0"/>
      <inertia ixx="3.841e-05" ixy="0" ixz="0" iyy="5.358e-06" iyz="8.642e-07" izz="4.031e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/top.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/top.stl" scale="1 1 1"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_0">
    <inertial>
      <mass value="0.0142"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="9.69363e-05" ixy="0" ixz="0" iyy="9.69363e-05" iyz="0" izz="0.000193532"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/tmotor_1344_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.1651" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_1">
    <inertial>
      <mass value="0.0142"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="9.69363e-05" ixy="0" ixz="0" iyy="9.69363e-05" iyz="0" izz="0.000193532"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/tmotor_1344_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.1651" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_2">
    <inertial>
      <mass value="0.0142"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="9.69363e-05" ixy="0" ixz="0" iyy="9.69363e-05" iyz="0" izz="0.000193532"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/tmotor_1344_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.1651" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_3">
    <inertial>
      <mass value="0.0142"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="9.69363e-05" ixy="0" ixz="0" iyy="9.69363e-05" iyz="0" izz="0.000193532"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/tmotor_1344_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.1651" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_4">
    <inertial>
      <mass value="0.0142"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="9.69363e-05" ixy="0" ixz="0" iyy="9.69363e-05" iyz="0" izz="0.000193532"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/tmotor_1344_ccw.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.1651" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <link name="propeller_5">
    <inertial>
      <mass value="0.0142"/>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <inertia ixx="9.69363e-05" ixy="0" ixz="0" iyy="9.69363e-05" iyz="0" izz="0.000193532"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_voliro_like_pt003_config/meshes/tmotor_1344_cw.stl" scale="1 1 1"/>
      </geometry>
      <material name="black">
        <texture/>
        <color rgba="0 0 0 1"/>
      </material>
    </visual>
    <collision>
      <origin xyz="0 0 0.006" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.1651" length="0.012"/>
      </geometry>
    </collision>
  </link>
  <joint name="arm_0_joint" type="tilt">
    <origin xyz="0.285788 0.165 0.029" rpy="0 -0 0.523599"/>
    <axis xyz="1 0 0"/>
    <parent link="base_link"/>
    <child link="arm_0"/>
    <limit effort="2.45166" velocity="26.1799" lower="-2.35619" upper="2.35619"/>
  </joint>
  <joint name="arm_1_joint" type="tilt">
    <origin xyz="2.02067e-17 0.33 0.029" rpy="0 -0 1.5708"/>
    <axis xyz="1 0 0"/>
    <parent link="base_link"/>
    <child link="arm_1"/>
    <limit effort="2.45166" velocity="26.1799" lower="-2.35619" upper="2.35619"/>
  </joint>
  <joint name="arm_2_joint" type="tilt">
    <origin xyz="-0.285788 0.165 0.029" rpy="0 -0 2.61799"/>
    <axis xyz="1 0 0"/>
    <parent link="base_link"/>
    <child link="arm_2"/>
    <limit effort="2.45166" velocity="26.1799" lower="-2.35619" upper="2.35619"/>
  </joint>
  <joint name="arm_3_joint" type="tilt">
    <origin xyz="-0.285788 -0.165 0.029" rpy="0 -0 -2.61799"/>
    <axis xyz="1 0 0"/>
    <parent link="base_link"/>
    <child link="arm_3"/>
    <limit effort="2.45166" velocity="26.1799" lower="-2.35619" upper="2.35619"/>
  </joint>
  <joint name="arm_4_joint" type="tilt">
    <origin xyz="-6.062e-17 -0.33 0.029" rpy="0 -0 -1.5708"/>
    <axis xyz="1 0 0"/>
    <parent link="base_link"/>
    <child link="arm_4"/>
    <limit effort="2.45166" velocity="26.1799" lower="-2.35619" upper="2.35619"/>
  </joint>
  <joint name="arm_5_joint" type="tilt">
    <origin xyz="0.285788 -0.165 0.029" rpy="0 -0 -0.523599"/>
    <axis xyz="1 0 0"/>
    <parent link="base_link"/>
    <child link="arm_5"/>
    <limit effort="2.45166" velocity="26.1799" lower="-2.35619" upper="2.35619"/>
  </joint>
  <joint name="battery_joint" type="fixed">
    <origin xyz="0 0 0.026" rpy="1.5708 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="battery"/>
  </joint>
  <joint name="fmu_joint" type="fixed">
    <origin xyz="0 0 0.058" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="fmu"/>
  </joint>
  <joint name="frame_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="body"/>
  </joint>
  <joint name="lg_base_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="base_link"/>
    <child link="lg_base_link"/>
  </joint>
  <joint name="lg_left_bottom_joint" type="revolute">
    <origin xyz="0 0 -0.0125" rpy="0 -0 0"/>
    <axis xyz="1 0 0"/>
    <parent link="lg_left_top"/>
    <child link="lg_left_bottom"/>
    <dynamics damping="0" friction="0.1"/>
    <limit effort="10" velocity="0.218166" lower="-0.01" upper="0.959931"/>
  </joint>
  <joint name="lg_left_top_joint" type="fixed">
    <origin xyz="0 0.0825 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="lg_base_link"/>
    <child link="lg_left_top"/>
  </joint>
  <joint name="lg_right_bottom_joint" type="revolute">
    <origin xyz="0 0 -0.0125" rpy="0 -0 0"/>
    <axis xyz="1 0 0"/>
    <parent link="lg_right_top"/>
    <child link="lg_right_bottom"/>
    <dynamics damping="0" friction="0.1"/>
    <limit effort="10" velocity="0.218166" lower="-0.01" upper="0.959931"/>
  </joint>
  <joint name="lg_right_top_joint" type="fixed">
    <origin xyz="0 -0.0825 0" rpy="0 -0 3.14159"/>
    <axis xyz="0 0 0"/>
    <parent link="lg_base_link"/>
    <child link="lg_right_top"/>
  </joint>
  <joint name="propeller_0_joint" type="thrust">
    <origin xyz="0 0 0.034" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="arm_0"/>
    <child link="propeller_0"/>
    <direction value="ccw"/>
  </joint>
  <joint name="propeller_1_joint" type="thrust">
    <origin xyz="0 0 0.034" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="arm_1"/>
    <child link="propeller_1"/>
    <direction value="cw"/>
  </joint>
  <joint name="propeller_2_joint" type="thrust">
    <origin xyz="0 0 0.034" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="arm_2"/>
    <child link="propeller_2"/>
    <direction value="ccw"/>
  </joint>
  <joint name="propeller_3_joint" type="thrust">
    <origin xyz="0 0 0.034" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="arm_3"/>
    <child link="propeller_3"/>
    <direction value="cw"/>
  </joint>
  <joint name="propeller_4_joint" type="thrust">
    <origin xyz="0 0 0.034" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="arm_4"/>
    <child link="propeller_4"/>
    <direction value="ccw"/>
  </joint>
  <joint name="propeller_5_joint" type="thrust">
    <origin xyz="0 0 0.034" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="arm_5"/>
    <child link="propeller_5"/>
    <direction value="cw"/>
  </joint>
</robot>


Transformable Multicopter (JSK Hydrus)

A quadcopter with four thrust joints and three revolute joints. Command values for the revolute joints can be freely specified by the user.

hydrus

Before XACRO expansion 
<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="hydrus">

  <!-- basic kinematics model -->
  <xacro:include filename="$(find tobas_description)/urdf/components/hydrus/common.xacro"/>
  <xacro:include filename="$(find tobas_description)/urdf/components/hydrus/link.uadf"/>

  <xacro:hydrus_link links="4" self="1" rotor_direction="-1" with_battery="0"/>
  <xacro:hydrus_link links="4" self="2" rotor_direction="1" with_battery="0"/>
  <xacro:hydrus_link links="4" self="3" rotor_direction="-1" with_battery="0"/>
  <xacro:hydrus_link links="4" self="4" rotor_direction="1" with_battery="0"/>

  <!-- special battery arrangement -->
  <xacro:extra_module name="bat1" parent="link1" visible="1" model_url="package://tobas_description/meshes/hydrus/battery/Kypom-3000-6s.dae">
    <origin xyz="${link_length/2} 0.0 -0.048" rpy="0 0 0"/>
    <inertial>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <mass value="0.4108"/>
      <inertia ixx="0.0001" iyy="0.0006" izz="0.0006" ixy="0.0" ixz="0.0" iyz="0.0"/>
    </inertial>
  </xacro:extra_module>

  <xacro:extra_module name="bat2" parent="link4" visible="1" model_url="package://tobas_description/meshes/hydrus/battery/Kypom-3000-6s.dae">
    <origin xyz="${link_length/2} 0.0 -0.048" rpy="0 0 0"/>
    <inertial>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <mass value="0.4108"/>
      <inertia ixx="0.0001" iyy="0.0006" izz="0.0006" ixy="0.0" ixz="0.0" iyz="0.0"/>
    </inertial>
  </xacro:extra_module>

  <!-- onboard -->
  <!-- 1.  processor -->
  <!-- 1.1 flight controller -->
  <xacro:extra_module name="fc" parent="link2" visible="1" model_url="package://tobas_description/meshes/hydrus/ver2/flight_controller/spinal.dae">    <!-- same with intel euclid -->
    <origin xyz="${link_length / 2 + 0.2221} ${-4.4*0.001} 0.02135" rpy="0 0 0"/>
    <inertial>
      <mass value="0.05"/>
      <origin xyz="${13*0.001} ${4.4*0.001} ${-9*0.001}" rpy="0 0 0"/>
      <inertia ixx="0.00001" ixy="0.0" ixz="0.0" iyy="0.00001" iyz="0.0" izz="0.00002"/>
    </inertial>
  </xacro:extra_module>
  <!-- end: flight controller -->

  <!-- 1.2 processor: jetson tx2 -->
  <!-- confirm the inertial parameter with real machine -->
  <xacro:extra_module name="pc" parent="link3" visible="1" model_url="package://tobas_description/meshes/hydrus/ver2/processor/jetson_tx2_unit.dae">
    <origin xyz="${link_length / 2 - 0.23775} 0.0 ${-0.01}" rpy="0 0 0"/>
    <inertial>
      <mass value="0.181"/>
      <origin xyz="${18 * 0.001} ${4 * 0.001} ${-18 * 0.001}" rpy="0 0 0"/>
      <inertia ixx="0.00007" ixy="0.0" ixz="0.0" iyy="0.00003" iyz="0.0" izz="0.00009"/>
    </inertial>
  </xacro:extra_module>
  <!-- end: processor: jetson tx2 -->

  <!-- 2.  sensor -->
  <!-- 2.1 leddar one -->
  <xacro:extra_module name="leddarone" parent="link3" visible="1" model_url="package://tobas_description/meshes/hydrus/sensor/leddar_one_tx2_attached_mode.dae">
    <origin xyz="${link_length/2 - 0.1855} 0.0 -0.0626" rpy="${pi} 0 0"/>
    <inertial>
      <origin xyz="-0.008 0.0 0.0" rpy="0 0 0"/>
      <mass value="0.025"/>
      <inertia ixx="0.00001" iyy="0.000006" izz="0.00001" ixy="0.000000" ixz="0.000000" iyz="0.000000"/>
    </inertial>
  </xacro:extra_module>
  <!-- end: leddar one -->

  <!-- 2.2 gps -->
  <xacro:extra_module name="gps" parent="link2" visible="1" model_url="package://tobas_description/meshes/hydrus/sensor/gps_ublox_m8n.dae">
    <origin xyz="${link_length/2 + 0.1925} 0.0 0.152" rpy="0 0 0"/>
    <inertial>
      <origin xyz="0.000000 0.000000 -0.013" rpy="0 0 0"/>
      <mass value="0.042"/>
      <inertia ixx="0.00006" iyy="0.00006" izz="0.000007" ixy="0.000000" ixz="0.000000" iyz="0.000000"/>
    </inertial>
  </xacro:extra_module>
  <xacro:extra_module name="magnet" parent="gps">
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <inertial>
      <mass value="0.00001"/>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="0.000001" ixy="0.0" ixz="0.0" iyy="0.000001" iyz="0.0" izz="0.000002"/>
    </inertial>
  </xacro:extra_module>
  <!-- end: gps -->

</robot>
After XACRO expansion 
<robot name="hydrus">
  <link name="bat1">
    <inertial>
      <mass value="0.4108"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="0.0001" ixy="0" ixz="0" iyy="0.0006" iyz="0" izz="0.0006"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/Kypom-3000-6s.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="bat2">
    <inertial>
      <mass value="0.4108"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="0.0001" ixy="0" ixz="0" iyy="0.0006" iyz="0" izz="0.0006"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/Kypom-3000-6s.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="fc">
    <inertial>
      <mass value="0.05"/>
      <origin xyz="0.013 0.0044 -0.009" rpy="0 -0 0"/>
      <inertia ixx="1e-05" ixy="0" ixz="0" iyy="1e-05" iyz="0" izz="2e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/spinal.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="gps">
    <inertial>
      <mass value="0.042"/>
      <origin xyz="0 0 -0.013" rpy="0 -0 0"/>
      <inertia ixx="6e-05" ixy="0" ixz="0" iyy="6e-05" iyz="0" izz="7e-06"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/gps_ublox_m8n.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="leddarone">
    <inertial>
      <mass value="0.025"/>
      <origin xyz="-0.008 0 0" rpy="0 -0 0"/>
      <inertia ixx="1e-05" ixy="0" ixz="0" iyy="6e-06" iyz="0" izz="1e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/leddar_one_tx2_attached_mode.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="leg1">
    <inertial>
      <mass value="0.0471"/>
      <origin xyz="0 0.0005 -0.09411" rpy="0 -0 0"/>
      <inertia ixx="0.000251" ixy="0" ixz="0" iyy="0.000242" iyz="0" izz="1.1e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/end_leg.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="leg2">
    <inertial>
      <mass value="0.0471"/>
      <origin xyz="0 0.0005 -0.09521" rpy="0 -0 0"/>
      <inertia ixx="0.000251" ixy="0" ixz="0" iyy="0.000242" iyz="0" izz="1.1e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/joint_leg.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="leg3">
    <inertial>
      <mass value="0.0471"/>
      <origin xyz="0 0.0005 -0.09521" rpy="0 -0 0"/>
      <inertia ixx="0.000251" ixy="0" ixz="0" iyy="0.000242" iyz="0" izz="1.1e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/joint_leg.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="leg4">
    <inertial>
      <mass value="0.0471"/>
      <origin xyz="0 0.0005 -0.09521" rpy="0 -0 0"/>
      <inertia ixx="0.000251" ixy="0" ixz="0" iyy="0.000242" iyz="0" izz="1.1e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/joint_leg.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="leg5">
    <inertial>
      <mass value="0.0471"/>
      <origin xyz="0 0.0005 -0.09411" rpy="0 -0 0"/>
      <inertia ixx="0.000251" ixy="0" ixz="0" iyy="0.000242" iyz="0" izz="1.1e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/end_leg.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="link1">
    <inertial>
      <mass value="0.58712"/>
      <origin xyz="0.357 0 0.018" rpy="0 -0 0"/>
      <inertia ixx="0.00179" ixy="0" ixz="0.00067" iyy="0.01605" iyz="0" izz="0.01714"/>
    </inertial>
    <visual>
      <origin xyz="0.3 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/link1.dae" scale="1 1 1"/>
      </geometry>
    </visual>
    <collision>
      <origin xyz="0.3 0 -0.08575" rpy="0 -0 0"/>
      <geometry>
        <box size="0.6 0.05 0.1715"/>
      </geometry>
    </collision>
  </link>
  <link name="link2">
    <inertial>
      <mass value="0.55744"/>
      <origin xyz="0.3 0 0.01287" rpy="0 -0 0"/>
      <inertia ixx="0.00171" ixy="0" ixz="1e-05" iyy="0.01727" iyz="0" izz="0.01844"/>
    </inertial>
    <visual>
      <origin xyz="0.3 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/link2.dae" scale="1 1 1"/>
      </geometry>
    </visual>
    <collision>
      <origin xyz="0.3 0 -0.08575" rpy="0 -0 0"/>
      <geometry>
        <box size="0.6 0.05 0.1715"/>
      </geometry>
    </collision>
  </link>
  <link name="link3">
    <inertial>
      <mass value="0.63453"/>
      <origin xyz="0.2683 0 0.01836" rpy="0 -0 0"/>
      <inertia ixx="0.00182" ixy="0" ixz="-0.00077" iyy="0.02232" iyz="0" izz="0.02254"/>
    </inertial>
    <visual>
      <origin xyz="0.3 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/link3.dae" scale="1 1 1"/>
      </geometry>
    </visual>
    <collision>
      <origin xyz="0.3 0 -0.08575" rpy="0 -0 0"/>
      <geometry>
        <box size="0.6 0.05 0.1715"/>
      </geometry>
    </collision>
  </link>
  <link name="link4">
    <inertial>
      <mass value="0.59"/>
      <origin xyz="0.242 0 0.0188" rpy="0 -0 0"/>
      <inertia ixx="0.00179" ixy="0" ixz="-0.00067" iyy="0.01581" iyz="0" izz="0.01692"/>
    </inertial>
    <visual>
      <origin xyz="0.3 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/link4.dae" scale="1 1 1"/>
      </geometry>
    </visual>
    <collision>
      <origin xyz="0.3 0 -0.08575" rpy="0 -0 0"/>
      <geometry>
        <box size="0.6 0.05 0.1715"/>
      </geometry>
    </collision>
  </link>
  <link name="magnet">
    <inertial>
      <mass value="1e-05"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="1e-06" ixy="0" ixz="0" iyy="1e-06" iyz="0" izz="2e-06"/>
    </inertial>
  </link>
  <link name="pc">
    <inertial>
      <mass value="0.181"/>
      <origin xyz="0.018 0.004 -0.018" rpy="0 -0 0"/>
      <inertia ixx="7e-05" ixy="0" ixz="0" iyy="3e-05" iyz="0" izz="9e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/jetson_tx2_unit.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>
  <link name="root"/>
  <link name="thrust1">
    <inertial>
      <mass value="0.0001"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="1e-05" ixy="0" ixz="0" iyy="1e-05" iyz="0" izz="2e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0.032" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/T-motor-CF-14inch-CW.dae" scale="1 1 1"/>
      </geometry>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.2025" length="0.1"/>
      </geometry>
    </collision>
  </link>
  <link name="thrust2">
    <inertial>
      <mass value="0.0001"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="1e-05" ixy="0" ixz="0" iyy="1e-05" iyz="0" izz="2e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0.032" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/T-motor-CF-14inch-CCW.dae" scale="1 1 1"/>
      </geometry>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.2025" length="0.1"/>
      </geometry>
    </collision>
  </link>
  <link name="thrust3">
    <inertial>
      <mass value="0.0001"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="1e-05" ixy="0" ixz="0" iyy="1e-05" iyz="0" izz="2e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0.032" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/T-motor-CF-14inch-CW.dae" scale="1 1 1"/>
      </geometry>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.2025" length="0.1"/>
      </geometry>
    </collision>
  </link>
  <link name="thrust4">
    <inertial>
      <mass value="0.0001"/>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <inertia ixx="1e-05" ixy="0" ixz="0" iyy="1e-05" iyz="0" izz="2e-05"/>
    </inertial>
    <visual>
      <origin xyz="0 0 0.032" rpy="0 -0 0"/>
      <geometry>
        <mesh filename="package://tobas_hydrus_config/meshes/T-motor-CF-14inch-CCW.dae" scale="1 1 1"/>
      </geometry>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 -0 0"/>
      <geometry>
        <cylinder radius="0.2025" length="0.1"/>
      </geometry>
    </collision>
  </link>
  <joint name="gps2magnet" type="fixed">
    <origin xyz="0 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="gps"/>
    <child link="magnet"/>
  </joint>
  <joint name="joint1" type="revolute">
    <origin xyz="0.6 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="link1"/>
    <child link="link2"/>
    <dynamics damping="0.9" friction="0.05"/>
    <limit effort="10" velocity="0.5" lower="-1.5708" upper="1.5708"/>
  </joint>
  <joint name="joint2" type="revolute">
    <origin xyz="0.6 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="link2"/>
    <child link="link3"/>
    <dynamics damping="0.9" friction="0.05"/>
    <limit effort="10" velocity="0.5" lower="-1.5708" upper="1.5708"/>
  </joint>
  <joint name="joint3" type="revolute">
    <origin xyz="0.6 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="link3"/>
    <child link="link4"/>
    <dynamics damping="0.9" friction="0.05"/>
    <limit effort="10" velocity="0.5" lower="-1.5708" upper="1.5708"/>
  </joint>
  <joint name="link12bat1" type="fixed">
    <origin xyz="0.3 0 -0.048" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link1"/>
    <child link="bat1"/>
  </joint>
  <joint name="link12leg1" type="fixed">
    <origin xyz="0.04116 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link1"/>
    <child link="leg1"/>
  </joint>
  <joint name="link22fc" type="fixed">
    <origin xyz="0.5221 -0.0044 0.02135" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link2"/>
    <child link="fc"/>
  </joint>
  <joint name="link22gps" type="fixed">
    <origin xyz="0.4925 0 0.152" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link2"/>
    <child link="gps"/>
  </joint>
  <joint name="link22leg2" type="fixed">
    <origin xyz="0 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link2"/>
    <child link="leg2"/>
  </joint>
  <joint name="link32leddarone" type="fixed">
    <origin xyz="0.1145 0 -0.0626" rpy="3.14159 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link3"/>
    <child link="leddarone"/>
  </joint>
  <joint name="link32leg3" type="fixed">
    <origin xyz="0 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link3"/>
    <child link="leg3"/>
  </joint>
  <joint name="link32pc" type="fixed">
    <origin xyz="0.06225 0 -0.01" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link3"/>
    <child link="pc"/>
  </joint>
  <joint name="link42bat2" type="fixed">
    <origin xyz="0.3 0 -0.048" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link4"/>
    <child link="bat2"/>
  </joint>
  <joint name="link42leg4" type="fixed">
    <origin xyz="0 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link4"/>
    <child link="leg4"/>
  </joint>
  <joint name="link42leg5" type="fixed">
    <origin xyz="0.55884 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="link4"/>
    <child link="leg5"/>
  </joint>
  <joint name="root_joint" type="fixed">
    <origin xyz="0 0 0" rpy="0 -0 0"/>
    <axis xyz="0 0 0"/>
    <parent link="root"/>
    <child link="link1"/>
  </joint>
  <joint name="rotor1" type="thrust">
    <origin xyz="0.3 0 0.013" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="link1"/>
    <child link="thrust1"/>
    <direction value="cw"/>
  </joint>
  <joint name="rotor2" type="thrust">
    <origin xyz="0.3 0 0.013" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="link2"/>
    <child link="thrust2"/>
    <direction value="ccw"/>
  </joint>
  <joint name="rotor3" type="thrust">
    <origin xyz="0.3 0 0.013" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="link3"/>
    <child link="thrust3"/>
    <direction value="cw"/>
  </joint>
  <joint name="rotor4" type="thrust">
    <origin xyz="0.3 0 0.013" rpy="0 -0 0"/>
    <axis xyz="0 0 1"/>
    <parent link="link4"/>
    <child link="thrust4"/>
    <direction value="ccw"/>
  </joint>
</robot>