<?xml version="1.0" ?>
<sdf version="1.5">
  <world name="default">
    <include>
      <uri>model://sun</uri>
    </include>

    <include>
      <uri>model://ground_plane</uri>
    </include>

    <model name="model_1">
      <pose>0 0 0 0 0 0</pose>

      <link name="link_1">
        <pose>0 0 0 0 0 0</pose>
        <collision name="collision_1">
          <geometry>
            <box>
              <size>1 1 1</size>
            </box>
          </geometry>
        </collision>
        <visual name="visual_1">
          <geometry>
            <box>
              <size>1 1 1</size>
            </box>
          </geometry>
        </visual>
      </link>

      <model name="model_2">
        <pose>0 0 1 0 0 0</pose>

        <link name="link_1">
          <pose>0 0 0 0 0 0</pose>
          <collision name="collision_1">
            <geometry>
              <box>
                <size>1 1 1</size>
              </box>
            </geometry>
          </collision>
          <visual name="visual_1">
            <geometry>
              <box>
                <size>1 1 1</size>
              </box>
            </geometry>
          </visual>
        </link>

        <link name="link_2">
          <pose>0 0 1 0 0 0</pose>
          <collision name="collision_2">
            <geometry>
              <box>
                <size>1 1 1</size>
              </box>
            </geometry>
          </collision>
          <visual name="visual_2">
            <geometry>
              <box>
                <size>1 1 1</size>
              </box>
            </geometry>
          </visual>
        </link>

        <joint name="joint_1" type="revolute">
          <parent>link_1</parent>
          <child>link_2</child>
          <pose>0 0 0 0 0 0</pose>
          <axis>
            <xyz>0 0 1</xyz>
          </axis>
        </joint>

      </model>

      <joint name="joint_1" type="revolute">
        <parent>link_1</parent>
        <child>model_2::link_1</child>
        <pose>0 0 0 0 0 0</pose>
        <axis>
          <xyz>0 0 1</xyz>
        </axis>
      </joint>
    </model>

  </world>
</sdf>
