Why spawned model keep falling down?

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Hi everyone,

After I launch gazebo.launch, the spawned model keep falling down to the floor, it seems controllers doesn't work. I did rosservice call /notspot_controller/controller_manager/list_controllers and it printed out: controller: [].

From terminal has warning: Controller Spawner couldn't find the expected controller_manager ROS interface., although I installed the needed package: sudo apt-get install ros-melodic-ros-control ros-melodic-joint-state-controller ros-melodic-effort-controllers ros-melodic-position-controllers ros-melodic-velocity-controllers ros-melodic-ros-controllers ros-melodic-gazebo-ros ros-melodic-gazebo-ros-control.

I have an urdf model notspot.urdf in here:

<?xml version="1.0" encoding="utf-8"?>
<!-- Author: lnotspotl -->

<!-- This URDF was automatically created by SolidWorks to URDF Exporter! Originally created by Stephen Brawner (brawner@gmail.com)
     Commit Version: 1.5.1-0-g916b5db  Build Version: 1.5.7152.31018
     For more information, please see http://wiki.ros.org/sw_urdf_exporter -->

<robot name="spot" xmlns:xacro="http://www.ros.org/wiki/xacro">

  <!-- Maximum torque -->
  <xacro:property name="effort_limit" value="1.4" />

  <!-- base_link -->
  <link name="base_link">
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://spot_description/meshes/body_obj.obj" />
      </geometry>
    </visual>
    <collision>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <box size="0.25 0.1285 0.055"/>
      </geometry>
    </collision>
  </link>

  <link name="base_inertia">
    <inertial>
      <origin xyz="-0.00048043 9.0814E-05 0.00023409" rpy="0 0 0" />
      <mass value="0.81776" />
      <inertia
        ixx="0.00058474"
        ixy="-1.0045E-06"
        ixz="1.0886E-08"
        iyy="0.00029699"
        iyz="3.2027E-08"
        izz="0.00063853" />
    </inertial>
  </link>

  <!-- FR1 -->
  <link name="FR1">
    <inertial>
      <origin xyz="0.011092 -0.0032719 0.00019267" rpy="0 0 0" />
      <mass value="0.15379" />
      <inertia
        ixx="4.474E-05"
        ixy="-1.0746E-05"
        ixz="-1.7651E-07"
        iyy="4.3489E-05"
        iyz="-7.8105E-08"
        izz="6.8646E-05" />
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://spot_description/meshes/FR1_obj.obj" />
      </geometry>
    </visual>
  </link>

    <!-- FR2 -->
  <link name="FR2">
    <inertial>
      <origin xyz="0.038603 -0.0025578 -0.0001752" rpy="0 0 0" />
      <mass value="0.15106" />
      <inertia
        ixx="2.365E-05"
        ixy="-5.3771E-07"
        ixz="-1.6144E-06"
        iyy="0.00010469"
        iyz="8.3059E-08"
        izz="0.00011187" />
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://spot_description/meshes/R2_obj.obj" />
      </geometry>
    </visual>
    <collision>
      <origin xyz="0.04 0 0" rpy="0 1.57075 0" />
      <geometry>
        <cylinder length="0.125" radius="0.014"/>
      </geometry>
    </collision>
  </link>

    <!-- FR3 -->
  <link name="FR3">
    <inertial>
      <origin xyz="0.029797 -0.00098828 -9.2749E-05" rpy="0 0 0" />
      <mass value="0.023372" />
      <inertia
        ixx="6.565E-07"
        ixy="6.8071E-07"
        ixz="-1.0503E-07"
        iyy="2.7257E-05"
        iyz="3.918E-09"
        izz="2.7469E-05" />
    </inertial>
    <visual>
      <origin xyz="0 0 0" rpy="0 0 0" />
      <geometry>
        <mesh filename="package://spot_description/meshes/R3_obj.obj" />
      </geometry> ...