Unmanned Systems Technology 027 l Hummingbird XRP l Gimbals l UAVs insight l AUVSI report part 2 l O’Neill Power Systems NorEaster l Kratos Defense ATMA l Performance Monitoring l Kongsberg Maritime Sounder

A team from Purdue University’s School of Engineering Technology in the US has taken inspiration from insects to come up with a novel design for a quadcopter that involves actively pivoting the arms on which the rotors are mounted (writes Peter Donaldson). Researchers Xiumin Diao, Jin Hu and Hao Xiong have published a paper describing their approach to optimising the energy efficiency of a quadrotor UAV by rotating its arms to positions derived from a dynamics model of the vehicle and the power-thrust curve of its rotors. The design was inspired by the wings and flight patterns of insects, and includes folding arms that can make in-flight adjustments, said Diao. Pivoting the arms moves the centre of lift with respect to the centre of gravity, which stabilises the aircraft and, because it allows the use of the full range of rotor thrust, increases energy efficiency. The researchers calculated the conditions under which the UAV can optimise its energy efficiency in steady-state flight, and analysed its efficiency in various scenarios. One scenario involved calculating the arm rotation approach that produced the best energy efficiency for a UAV in a steady hover with an offset centre of gravity. In simulation, they demonstrated the ability to reduce energy consumption by 13% compared with a conventional design, and said experiments have shown that the same vehicle can make larger savings in practice. The team plotted the power consumed by a rotor against the thrust generated by it, to gauge its efficiency. With torque sensors on each motor, they were able to measure bias torque along the x and y axes, plotting them against each other, against total thrust and against power, with low bias torque figures indicating greater efficiency. For example, comparing bias torque along the y axis for a conventional UAV with one with rotatable arms showed that the curve for the latter is much shallower, and rises to a lower peak of less than 300 W at 5 Nm compared with almost 350 W. Insects help UAV design Airborne vehicles The insect-inspired quadcopter’s pivoting arms help to optimise its energy efficiency (Courtesy of Purdue University)