The weight, space, and power limitations of small aerial vehicles often
prevent the application of modern control techniques without significant model
simplifications. Moreover, high-speed agile behavior, such as that exhibited in
drone racing, make these simplified models too unreliable for safety-critical
control. In this work, we introduce the concept of time-varying backup
controllers (TBCs): user-specified maneuvers combined with backup controllers
that generate reference trajectories which guarantee the safety of nonlinear
systems. TBCs reduce conservatism when compared to traditional backup
controllers and can be directly applied to multi-agent coordination to
guarantee safety. Theoretically, we provide conditions under which TBCs
strictly reduce conservatism, describe how to switch between several TBC's and
show how to embed TBCs in a multi-agent setting. Experimentally, we verify that
TBCs safely increase operational freedom when filtering a pilot's actions and
demonstrate robustness and computational efficiency when applied to
decentralized safety filtering of two quadrotors.Comment: Submitted to IROS 202