We present HUM-High-frequency UAV Messaging: an acoustic side channel communication system we design for localized drone-to-drone communications. We generate Pulse Width Modulated (PWM) signals from drone motors to carry information and improve communication reliability by mitigating propeller noise interference through modifications to the propeller's physical design. These modifications reduce propeller noise in the designated acoustic spectrum by up to 7 dB. We deploy a custom ultrasonic microphone shield specifically designed for decoding in the receiver. HUM's improved signal-to-noise ratio enables up to 80x higher data rates compared to the existing design from the literature while providing better scalability. HUM supports simultaneous decoding across 16 drones within 8 m, range as seen in real flight tests. The cost of this performance is minimal; we experimentally demonstrate that HUM has a marginal impact on flight dynamics and battery life.

In recent times, Unmanned Aerial Vehicles (UAVs) have been intensively studied for a wide range of military and civil applications such as surveillance and reconnaissance missions, agriculture, traffic monitoring, pollution control, meteorological data collection, pipeline survey, early fire detection, rescue missions, wildlife population monitoring, etc. The above tasks can be carried out faster and more efficiently by a group of UAVs flying in formation. This paper presents the application of two stage switching controller in autonomous formation flight of UAVs based on the leader follower configuration. The constructed UAV airframe, as well as the autopilot, formation flight control unit and wireless communication link for data sharing between UAVs were presented and described. The advantages of the switched control were demonstrated in terms of a significantly larger region of stability in maintaining formation, as opposed to the standard, one stage control laws with classical compensators. Hardware In The Loop (HIL) tests of proposed formation flight control were performed, during which the inertial states and flight parameters were logged. The HIL test rig enabled us to verify the formation flight control performance which was further substantiated by actual flight tests.