Integration of a Load Cell in a Hexacopter UAS Failsafe Propulsion Arm for Inflight Thrust Measurement

Accurate thrust measurement of multicopter UAS propulsion systems is necessary across various fields, including for UA performance research as well as in UAS deployment, especially for lifting operations using multirotor unmanned aircraft. This paper details the development of a multicopter propulsion arm with an integrated load cell, capable of measuring the thrust generated by the mounted rotor. Hence the thrust generated by the individual rotors of the hexacopter UA whilst being operated in the open field may be accurately measured and subsequently logged. The mounting adopts a failsafe design that permits the motor to provide the necessary rotor propulsion even when the load cell unit fails, allowing the safe landing of the hexacopter UA and avoiding the loss of the aircraft. The mounting assembly was statically characterized for the load cell response across a range of applied loads. Numerical models for the load cell response were developed, based on a Machine Learning Gradient Boosting Regressor, whilst analytical models based on the Bouc-Wen and Preisach models were also developed. The Machine Learning Gradient Boosting Regressor model returned the closest estimate to the true applied load with a reduction in RMSE of 36.6 % when compared to the raw load cell data.