Quadrotor control improves safety under limited rotation speeds
Escape-Aware Control Barrier Functions for Quadrotor Safety under Body-Rate Limits
Robotics
Summary
Controlling quadrotors to stay safe can be tricky because their engines need time to redirect thrust, and they can only rotate so fast. The authors show that usual safety checks, based only on current position and speed, can miss dangerous cases where the quadrotor cannot stop or escape in time. They create a new safety measure that also considers recent controls, allowing for better prediction and safer flight. Their tests show this method helps quadrotors avoid crashes that older methods miss.
What this means in practice
- •For autonomous drone developers: Improve quadrotor flight safety by accounting for limited rotation speed in control algorithms to prevent crashes in tight maneuvers.
- •For robotics control engineers: Incorporate body-rate-aware barrier functions into predictive controllers to certify safe states more accurately under actuator limits.
Authors
Lei Shi, Haosong Wen, Qichao Liu
Abstract
Control barrier functions for input-constrained systems place the admissible input set inside the definition of the safe set, yet the resulting barrier is almost always a function of the state alone; On a quadrotor this is not cosmetic: because the thrust vector must be reoriented before it can decelerate an approach, and reorientation is limited by the attainable body rate, a state-only barrier certifies states from which no escape is reachable in time; We characterize the certification gap in closed form and show its width is proportional to closing speed and inversely proportional to the body-rate limit; We then define an escape barrier on the augmented pair of state and previously applied input, with escape authority measured over the one-step reachable thrust cap; It admits a closed form and an analytic inverse for the maximum certifiable closing speed, and embeds in a predictive controller at no additional state cost; Across 550 paired closed-loop episodes on a 13-state quadrotor, the proposed controller completes every tested scenario, whereas the stopping-distance barrier enforced over the same horizon fails 15% and 25% of episodes in exactly the two scenarios that enter the predicted gap; Against an online backup-CBF baseline enforcing the same escape condition at the reached state, it holds a 29-74 degree larger directional margin and 3-18 times the clearance, and an independent conservative rollout referee finds no certified state from which escape fails.