how to use robot_mechanism_controllers/JointVelocityController ?

edit

In brief: how to public message to the topic that one sample robot_mechanism_controllers/JointVelocityController subscribes?

I launched my robot_mechanism_controllers/JointVelocityController with this yaml file:

r_shoulder_pan_joint_controller:   
 type: robot_mechanism_controllers/JointVelocityController  
 joint: r_shoulder_pan_joint  
 pid:   
   p: 10.0  
   i: 0.0  
   d: 0.0  
   i_clamp: 0.0

and I published to the topic "/r_shoulder_pan_joint_controller/command".

In my rxgraph terminal I could see that the publisher is working however the "r_shoulder_pan_joint_controller" is not subscribing. Its connection is like:

Connections:
  * topic: /rosout
   * to: /rosout
   * direction: outbound
   * transport: TCPROS
 * topic: /clock
   * to: /gazebo (<a href="http://localhost:39443/">http://localhost:39443/</a>)
   * direction: inbound
   * transport: TCPROS

In addition after the "gazebo" node received the message (that I published), it publishes it to itself instead of to "r_shoulder_pan_joint_controller" node:

topic: /r_shoulder_pan_joint_controller/command
* to: <a href="http://localhost:55720/">http://localhost:55720/</a>
* direction: inbound
* transport: TCPROS

I suppose "to: http://localhost:55720/" should be "to: /r_shoulder_pan_joint_controller"

Any hint/suggestion/discussion is very much welcome! Thanks!

Yuquan