Higher-order and torque-aware safety filters for thrust-direction singularities

Develop higher-order or torque-aware safety filters for quadrotor configurations in which the relative-position vector is nearly orthogonal to both available thrust directions, causing poor instantaneous control authority for the second-order distance constraint.

Background

The paper’s robust HOCBF-QP modifies only the scalar thrust magnitudes, while body torques influence collision avoidance indirectly through the evolution of the quadrotor attitudes and thrust directions. The safety guarantee is conditional on feasibility of this QP. When the relative-position vector is nearly orthogonal to both agents’ thrust directions, changing thrust magnitudes has weak effect on the second derivative of the pairwise distance, so thrust bounds can make the QP infeasible or ineffective. The authors explicitly identify higher-order and torque-aware filters as unresolved approaches for handling these singular configurations.