Velocity Instantaneously x Velocity With Joint Motors and How to Use

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Hi everyone,

I'm trying to control the height of a UAV using predictive control. To do so I'm using the "Iris with Standoff" model, but I'm having some trouble to set the velocity of the rotor's joint. I followed the tutorial "Setting Velocity on Links And Joints" (http://gazebosim.org/tutorials?tut=se...) and tried to use the "Set Velocity Instantaneously", but the UAV doesn't take off, independent of the velocity that I set, even though the rotors rotate. It seems to me, that I should set the velocity with joint motors, but I didn't understand how to use. I can't set the velocity using PID Controllers, because that is already in my controller. I'm setting the velocity with a plugin that is subscribed in a ROS Topic, all the "ROS Thing" is working, I followed the velodyne tutorial (http://gazebosim.org/tutorials?tut=gu...). So, in my situation, how should I set the velocity? Instantaneously or with joint motors? And how can I do this?

I'm using Gazebo7, ROS Kinetic and Ubuntu 16.04.

The model.sdf and the plugin that i developed are below. Sorry if the post is too big, it is because of the models and plugins code, first time here.

Mode.sdf

<?xml version='1.0'?>
<sdf version='1.6'>
  <model name='iris'>
    <pose>0 0 0.194923 0 0 0</pose>
    <link name='base_link'>
      <velocity_decay>
        <linear>0.0</linear>
        <angular>0.0</angular>
      </velocity_decay>
      <inertial>
        <pose>0 0 0 0 0 0</pose>
        <mass>0.468</mass>
        <inertia>
          <ixx>0.004856</ixx>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyy>0.004856</iyy>
          <iyz>0</iyz>
          <izz>0.008801</izz>
        </inertia>
      </inertial>
      <collision name='base_link_collision'>
        <pose>0 0 -0.08 0 0 0</pose>
        <geometry>
          <box>
            <size>0.47 0.47 0.23</size>
          </box>
        </geometry>
        <surface>
          <contact>
            <ode>
              <max_vel>100.0</max_vel>
              <min_depth>0.001</min_depth>
            </ode>
          </contact>
          <friction>
            <ode>
              <mu>1.0</mu>
              <mu2>1.0</mu2>
            </ode>
          </friction>
        </surface>
      </collision>
      <visual name='base_link_visual'>
        <geometry>
          <mesh>
            <uri>model://iris_with_standoffs/meshes/iris.dae</uri>
          </mesh>
        </geometry>
        <material>
          <script>
            <name>Gazebo/DarkGrey</name>
          </script>
        </material>
      </visual>

      <visual name='front_left_leg_visual'>
        <pose>0.123 0.22 -0.11 0 0 0</pose>
        <geometry>
          <cylinder>
            <radius>0.005</radius>
            <length>0.17</length>
          </cylinder>
        </geometry>
        <material>
          <script>
            <name>Gazebo/FlatBlack</name>
            <uri>file://media/materials/scripts/gazebo.material</uri>
          </script>
        </material>
      </visual>
      <visual name='front_right_leg_visual'>
        <pose>0.123 -0.22 -0.11 0 0 0</pose>
        <geometry>
          <cylinder>
            <radius>0.005</radius>
            <length>0.17</length>
          </cylinder>
        </geometry>
        <material>
          <script>
            <name>Gazebo/FlatBlack</name>
            <uri>file://media/materials/scripts/gazebo.material</uri>
          </script>
        </material>
      </visual>
      <visual name='rear_left_leg_visual'>
        <pose>-0.140 0.21 -0.11 0 0 0</pose>
        <geometry>
          <cylinder>
            <radius>0.005</radius>
            <length>0.17</length>
          </cylinder>
        </geometry>
        <material>
          <script>
            <name>Gazebo/FlatBlack</name>
            <uri>file://media/materials/scripts/gazebo.material</uri>
          </script>
        </material>
      </visual>
      <visual name='rear_right_leg_visual'>
        <pose>-0.140 -0.21 -0.11 0 ...