Locomotion is supplied by a Lego Power Function motor controller. He cut an LPF extension wire in half so that he could patch into the PWM signals without altering the motors themselves.

Enhancing Lego Mindstorms with Arduino Lego Mindstorms NXT is a sophisticated and fun educational robotics set that teaches kids and adults engineering and programming skills.

A Stack Exchange post on a brick’s “clutch power” leads to a 10-day experiment.