How can I attach different models on a new model. I am unable to attach a camera model to my quadcopter model

edit

I am working on adding a camera model to my Iris Quadcopter. It has Optical Flow camera and Lidar. When I add a new camera, the camera gets left out and it will not stay with my quadcopter.

here is my different model:

Iris:

<sdf version='1.6'>
  <model name='iris'>
    <link name='base_link'>
      <pose frame=''>0 0 0 0 -0 0</pose>
      <inertial>
        <pose frame=''>0 0 0 0 -0 0</pose>
        <mass>1.5</mass>
        <inertia>
          <ixx>0.0347563</ixx>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyy>0.0458929</iyy>
          <iyz>0</iyz>
          <izz>0.0977</izz>
        </inertia>
      </inertial>
      <collision name='base_link_inertia_collision'>
        <pose frame=''>0 0 0 0 -0 0</pose>
        <geometry>
          <box>
            <size>0.47 0.47 0.11</size>
          </box>
        </geometry>
        <surface>
          <contact>
            <ode>
              <min_depth>0.001</min_depth>
              <max_vel>0</max_vel>
            </ode>
          </contact>
          <friction>
            <ode/>
          </friction>
        </surface>
      </collision>
      <visual name='base_link_inertia_visual'>
        <pose frame=''>0 0 0 0 -0 0</pose>
        <geometry>
          <mesh>
            <scale>1 1 1</scale>
            <uri>model://rotors_description/meshes/iris.stl</uri>
          </mesh>
        </geometry>
        <material>
          <script>
            <name>Gazebo/DarkGrey</name>
            <uri>file://media/materials/scripts/gazebo.material</uri>
          </script>
        </material>
      </visual>
      <gravity>1</gravity>
      <velocity_decay/>
    </link>
    <link name='/imu_link'>
      <pose frame=''>0 0 0 0 -0 0</pose>
      <inertial>
        <pose frame=''>0 0 0 0 -0 0</pose>
        <mass>0.015</mass>
        <inertia>
          <ixx>1e-05</ixx>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyy>1e-05</iyy>
          <iyz>0</iyz>
          <izz>1e-05</izz>
        </inertia>
      </inertial>
    </link>
    <joint name='/imu_joint' type='revolute'>
      <child>/imu_link</child>
      <parent>base_link</parent>
      <axis>
        <xyz>1 0 0</xyz>
        <limit>
          <lower>0</lower>
          <upper>0</upper>
          <effort>0</effort>
          <velocity>0</velocity>
        </limit>
        <dynamics>
          <spring_reference>0</spring_reference>
          <spring_stiffness>0</spring_stiffness>
        </dynamics>
        <use_parent_model_frame>1</use_parent_model_frame>
      </axis>
    </joint>
    <link name='rotor_0'>
      <pose frame=''>0.13 -0.22 0.023 0 -0 0</pose>
      <inertial>
        <pose frame=''>0 0 0 0 -0 0</pose>
        <mass>0.005</mass>
        <inertia>
          <ixx>9.75e-07</ixx>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyy>0.000273104</iyy>
          <iyz>0</iyz>
          <izz>0.000274004</izz>
        </inertia>
      </inertial>
      <collision name='rotor_0_collision'>
        <pose frame=''>0 0 0 0 -0 0</pose>
        <geometry>
          <cylinder>
            <length>0.005</length>
            <radius>0.128</radius>
          </cylinder>
        </geometry>
        <surface>
          <contact>
            <ode/>
          </contact>
          <friction>
            <ode/>
          </friction>
        </surface>
      </collision>
      <visual name='rotor_0_visual'>
        <pose frame=''>0 0 0 0 -0 0</pose>
        <geometry>
          <mesh>
            <scale>1 1 1</scale>
            <uri>model://rotors_description/meshes/iris_prop_ccw.dae</uri>
          </mesh>
        </geometry>
        <material>
          <script>
            <name>Gazebo/Blue</name>
            <uri>file://media/materials/scripts/gazebo.material</uri>
          </script>
        </material>
      </visual>
      <gravity>1</gravity>
      <velocity_decay/>
    </link>
    <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>
        </limit>
        <dynamics>
          <spring_reference>0</spring_reference>
          <spring_stiffness>0</spring_stiffness>
        </dynamics>
        <use_parent_model_frame>1</use_parent_model_frame>
      </axis>
    </joint>
    <link name='rotor_1'>
      <pose frame=''>-0.13 0.2 0.023 0 -0 0</pose>
      <inertial>
        <pose frame=''>0 0 0 0 -0 0</pose>
        <mass>0.005</mass>
        <inertia>
          <ixx>9.75e-07</ixx>
          <ixy>0</ixy>
          <ixz>0</ixz ...