If you want to do full crab like the one in the article, not just front wheels like in the oldies video, you need to power the wheels. With 4 independent driving wheels you can switch between traditional 2 wheel steer, 4 wheel steer, crab (for parallel parking) and orbit for turning around in place. There is no transmission axle between the wheels so they can be independently rotated and controlled, just like on a film dolly.