How can I see the velocity response graph?

Hello ROS users: I am using linux 14.04, Ros indigo and Gazebo2. I would like to know how I can visualize the velocity response graph of my p3dx model. I explain it: I have a p3dx model in Gazebo and I send angular and linear velocity to it with "rostopic pub..." , so I would like to visualize the velocity response of the model p3dx with rqt because I want to know the time constant of my model. It seems like pose turtlebox in this tutorial http://wiki.ros.org/ROS/Tutorials/UnderstandingTopics (point 1.5) but with /p3dx/cmd_vel topic to visualize. How can I do that? Thank you so much!