ROS2 Control - Velocity Controller

Problem Statement

Implement a velocity controller node that drives a robot along a parameterized motion pattern and publishes velocity commands to /cmd_vel.

Requirements

Your node must:

• Declare parameters: max_linear_speed (default 0.5 m/s) and max_angular_speed (default 1.0 rad/s)
• Create a publisher for geometry_msgs/Twist on /cmd_vel
• Create a create_timer(0.1, ...) (10 Hz) control loop
• In each control loop iteration:
  • Build a Twist message with non-zero linear.x or angular.z (or both)
  • Clamp linear.x to [-max_linear_speed, max_linear_speed]
  • Clamp angular.z to [-max_angular_speed, max_angular_speed]
  • Publish the Twist message
• Publish at least 5 messages during the test window
• Log "Velocity Controller Ready" on startup

Input / Output

Output: geometry_msgs/Twist on /cmd_vel at 10 Hz

🤖 Why This Matters in Real Robots

This is the interface contract for every differential drive robot: differential drive controllers, omni-wheel controllers, and skid-steer controllers all listen on /cmd_vel and convert Twist into individual wheel velocities. Understanding this interface — and its limits — is prerequisite knowledge for working with ros2_control, Nav2, or writing any teleoperation interface.

⚠️ Common Pitfalls

• Publishing zero Twist: A default-constructed Twist() has all zeros. The robot won't move. Your control loop must set at least one non-zero field.
• Speed limits not from parameters: Hard-coding 0.5 instead of reading self.get_parameter('max_linear_speed').value defeats the purpose of parameterisation.