Custom_Bot get_model_state frame_id is "", and odom output

edit

Hi, sorry it's a bit long question. i have a 4 wheel custombot, the problem is i dont have any odom output, when i use rosserver

rosservice call /gazebo/get_model_state "model_name: 'rover' "

i get frame id is blank, and linear and angular twist is near zero. Is there any way to make the twists 0 when the bot is not moving, also my main concern is why the frame_id is blank?

    header: 
  seq: 3
  stamp: 
    secs: 6778
    nsecs: 359000000
  frame_id: ''
pose: 
  position: 
    x: 0.914803052943
    y: -0.0530903805427
    z: 0.0999992861131
  orientation: 
    x: 9.77827171294e-08
    y: -4.60199492012e-07
    z: -0.0135620999519
    w: 0.999908030493
twist: 
  linear: 
    x: -2.27657820656e-05
    y: -0.000137324696237
    z: 0.0048809205918
  angular: 
    x: 5.48403843617e-06
    y: -1.14813782152e-06
    z: -1.01071109906e-05
success: True
status_message: "GetModelState: got properties"

and as i'm new, what is publishing here? and how do i get odometry output in position from my robot? as it is a custom robot i have these topic from my robot:

/clock
/gazebo/link_states
/gazebo/model_states
/gazebo/parameter_descriptions
/gazebo/parameter_updates
/gazebo/set_link_state
/gazebo/set_model_state
/gazebo_gui/parameter_descriptions
/gazebo_gui/parameter_updates
/rosout
/rosout_agg
/rover/joint_states
/rover/laser/scan
/rover/left_back_wheel_controller/command
/rover/left_front_wheel_controller/command
/rover/right_back_wheel_controller/command
/rover/right_front_wheel_controller/command
/tf
/tf_static

i'm using following plugin:

<plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">