TurtleBot3 Waffle PI /cmd_vel topic is not active

edit

On the TB3 Waffle PI, I am implementing interactive markers and have this following rqt_graph showing all nodes and topics: Nodes and Topics. However, when I change the graph so that it only shows the active nodes and topics, it gives this: Active Nodes and Topics. I have no idea why this is happening. How can I make this topic active so that it can actively subscribe and publish messages over it?

I am using Ubuntu 16.04 and ROS Kinetic Kame.

Thank you in advance!