  Autonomous navigation in unknown environments with obstacles remains
challenging for micro aerial vehicles (MAVs) due to their limited onboard
computing and sensing resources. Although various collision avoidance methods
have been developed, it is still possible for drones to collide with unobserved
obstacles due to unpredictable disturbances, sensor limitations, and control
uncertainty. Instead of completely avoiding collisions, this article proposes
Air Bumper, a collision detection and reaction framework, for fully autonomous
flight in 3D environments to improve the safety of drones. Our framework only
utilizes the onboard inertial measurement unit (IMU) to detect and estimate
collisions. We further design a collision recovery control for rapid recovery
and collision-aware mapping to integrate collision information into general
LiDAR-based sensing and planning frameworks. Our simulation and experimental
results show that the quadrotor can rapidly detect, estimate, and recover from
collisions with obstacles in 3D space and continue the flight smoothly with the
help of the collision-aware map. Our Air Bumper will be released as open-source
software on GitHub.
