Direct thrust and velocity measurement for a micro UAV rotor

Thrust and velocity sensing is very important for the control of micro UAVs. Contemporary high-performance quadrotor motion control relies on accurate high-speed trajectory sensing. However, position and velocity sensing is challenging outside of an indoor Vicon arena: GPS is slow and noisy, optical flow sensors do not work far from ground, and pitot tubes perform poorly at low speeds. Our approach is to use a compact force-torque sensor to directly measure rotor forces and pitch-roll torques. The sensor is constructed from MEMS barometers encapsulated in an elastic compound, attached to a load plate. The sensor can provide sub-mN thrust force sensing at 1 kHz, with torque sensitivity better than 0.1 mN-m. Using a lumped parameter model of rotor induced drag and flapping torque-velocity coupling, we can accurately estimate translational velocity of a rotor. The velocity output is linear for translational velocities from below 0.25 to over 0.8 ms