Imitating the Katamari series, players push the real-life ball forward to roll up objects in-game. The controller works by rolling the ball on a fixed base with two optical computer mice attached to it. Each functions as one of the PlayStation 2's thumb sticks; whenever the ball is moved in any direction, it hits both mice together and acts like a player's thumbs would on a regular controller.
Check out the video above to see the ball work. LeBlanc posted photos and detailed the project's hardware and assembly on his blog.