Controllers
Controllers are the heart of your robot system, without a controller your robot does very little. The controller reads sensors, performs the required decision making, and implements the plan of action by manipulating the relevant actuators.
But the controller does NOTHING without you.
You prepare the controller by programming it on the PC, then connect the controller to the PC (throught the USB port), download the compiled program to the robot, disconnect the robot from the PC, and start the program running in the controller... and your robot is FREE.