Hi all,

I am trying to convert the following URDF into SDF using gz sdf -p model.urdf > model.sdf. I am trying to make sure the implicit spring damper is set to 1 through a gazebo reference. But in the output i get a duplicate.

INPUT URDF

<?xml version="1.0" ?>
<robot name="iris">
  <origin rpy="0 0 0" xyz="0    0     0.194923"/>

  <link name="base_link">
    <inertial>
      <mass value="1.5"/>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <inertia ixx="0.008" ixy="0" ixz="0" iyy="0.015" iyz="0" izz="0.017"/>
    </inertial>
    <collision name="base_link">
      <origin rpy="0 0 0" xyz="0      0      -0.08"/>
      <geometry>
        <box size="0.47 0.47 0.23"/>
      </geometry>
    </collision>
    <visual name="base_link">
      <geometry>
        <mesh filename="package://pysdf/scripts/meshes/iris.dae" scale="1.0 1.0 1.0"/>
      </geometry>
    </visual>
  </link>

  <link name="rotor_0">
    <inertial>
      <mass value="0.025"/>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <inertia ixx="9.75e-06" ixy="0" ixz="0" iyy="0.000166704" iyz="0" izz="0.000167604"/>
    </inertial>
    <collision name="rotor_0">
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <cylinder length="0.005" radius="0.1"/>
      </geometry>
    </collision>
    <visual name="rotor_0">
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <mesh filename="package://pysdf/scripts/meshes/iris_prop_ccw.dae" scale="1 1 1"/>
      </geometry>
    </visual>
  </link>

  <joint name="rotor_0_joint" type="revolute">
    <parent link="base_link"/>
    <child link="rotor_0"/>
    <origin rpy="0 0 0" xyz="0.13    -0.22     0.023"/>
    <axis xyz="0 0 1"/>
    <dynamics damping="0.004"/>
    <limit effort="-1" lower="-1e+16" upper="1e+16" velocity="-1"/>
  </joint>

  <gazebo reference="rotor_0">
    <collision name='rotor_0_collision'>
      <surface>
        <contact>
          <ode/>
        </contact>
        <friction>
          <ode/>
        </friction>
      </surface>
    </collision>
    <visual name='rotor_0_visual'>
      <material>
        <script>
          <name>Gazebo/Blue</name>
          <uri>__default__</uri>
        </script>
      </material>
    </visual>
    <self_collide>0</self_collide>
  </gazebo>

  <gazebo reference="rotor_0_joint">
    <physics>
      <ode>
         <implicit_spring_damper>1</implicit_spring_damper>
      </ode>
    </physics>
  </gazebo>

</robot>

The generated SDF returns multiple physics tags. Is it possible to combine them into the one tag upon upon conversion from URDF to SDF?

OUTPUT SDF (partial)

<joint name='rotor_0_joint' type='revolute'>
  <child>rotor_0</child>
  <parent>base_link</parent>
  <axis>
    <xyz>0 0 1</xyz>
    <limit>
      <lower>-1e+16</lower>
      <upper>1e+16</upper>
      <effort>-1</effort>
      <velocity>-1</velocity>
    </limit>
    <dynamics>
      <damping>0.004</damping>
      <friction>0</friction>
      <spring_reference>0</spring_reference>
      <spring_stiffness>0</spring_stiffness>
    </dynamics>
    <use_parent_model_frame>1</use_parent_model_frame>
  </axis>
  <physics>
    <ode>
      <limit>
        <cfm>0</cfm>
        <erp>0.2</erp>
      </limit>
    </ode>
  </physics>
  <physics>
    <ode>
      <implicit_spring_damper>1</implicit_spring_damper>
    </ode>
  </physics>
</joint>

Notice there are TWO physics tags! Does Gazebo9 automatically merge the two Physics tags and their contents together or does it only read one of them?

Thanks