Modeling and Control for Dynamic Drifting Trajectories

Passenger vehicles are conventionally designed to understeer at the limit of handling. While cornering with maximum lateral acceleration, the front tires tend to reach the friction limit before the rear. This means the vehicle’s rotational dynamics remain predictable and stable - but at the expense of controllability. When the front tires are friction saturated, additional steering input can no longer alter the vehicle’s trajectory [1] . In contrast, limit oversteer – cornering with rear tires at the friction limit – offers the opposite trade-off. The vehicle maintains controllability despite operating at the saturation limit of the rear tires, but the rotational dynamics become unstable [2] . However, in this region of the state space unstable equilibria exist that the vehicle can operate around [3] . This is the foundation of the sport of drifting - a cornering technique that involves deliberately oversteering and then countersteering so that the vehicle maintains a large sideslip angle. A skilled driver can exploit the stability-controllability trade-off and perform agile maneuvers despite operating at the friction limit.