Control the robot directly

Understand the velocity interface

The ROX base subscribes to the /cmd_vel topic using the geometry_msgs/Twist message type. The message carries linear and angular velocity commands.

Any process that publishes to /cmd_vel can control the base. Navigation2 uses this same interface, so it is one publisher to the robot rather than a privileged control path.

Open a sourced terminal in the robot container:

    

        
        
source ~/workshop_env.bash

    

Control the robot with the keyboard

Start keyboard teleoperation:

    

        
        
just teleop

    

Use the key bindings displayed in the terminal to drive the robot while you observe its movement in RViz.

Publish a velocity command

You can also publish forward velocity at 0.2 m/s and a fixed rate of 10 Hz:

    

        
        
ros2 topic pub --rate 10 /cmd_vel geometry_msgs/msg/Twist "{linear: {x: 0.2}}"

    

Let the command run for approximately three seconds, then press Ctrl+C to stop the publisher. Explicitly stop the robot by publishing a zero-velocity command:

    

        
        
ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist "{}"

    

These commands use the same /cmd_vel interface as teleoperation and Navigation2.

Verify movement with odometry

Read one odometry message and display the robot position:

    

        
        
ros2 topic echo /odom --once | grep -A2 position

    

The x position should advance when the robot moves. On the supplied reference system, a 3-second command at 0.2 m/s moved the robot from approximately x = 0 to x = 0.39 m:

    

        
              x: 0.3899999883542309

        
    

This value is an example, not an exact target. Acceleration behaviour and the robot’s starting position affect the result.

What you’ve learned and what’s next

You’ve controlled the robot through the same velocity interface used by Navigation2 and confirmed its movement through /odom. Next, you’ll inspect the CPU cost, simulation speed, and internal traffic of the running system.