Model-Based Engineering for Design Space Exploration of VTOL UAS’s
Sponsor: Army Research Laboratory
The objective of this project is to develop and validate performance prediction models for the electric powertrains of group 1 unmanned aerial systems (G1UAS) that use a sensorless brushless DC (BLDC) motor architecture consisting of a BLDC motor, electronic speed controller, and a battery. Per US Army definitions, G1UAS are platforms that weigh less than 9 kg (20 lb). The resulting semi-empirical models for the motor, power electronics, and battery use high-level component specifications to enable pre-conceptual design space exploration and mission-based design optimization of G1UAS without a library of test data. The models also enable tradeoffs analysis between existing and/or conceptual designs without a series of flight tests. To develop, tune, and validate the models, a custom dynamometer test setup was designed and built to measure torque, speed, and electrical power data of small-scale motor drive systems. The validated models reveal that popular claims of “high efficiency” for electric powertrains are only valid in a narrow band of high speed/low torque operation. This is a critical finding for vehicle designers in the VTOL industry who are increasingly transitioning to electric powertrains in low speed/high torque applications which may decrease the overall system efficiency. A traditional rotor hover test stand was also developed to generate data with a traditional rotor load. The integrated motor and electronic speed controller model was able to predict the total efficiency of the hover stand tests within 5 percent of experimental values. Sizing models are currently being developed, which will be able to predict the size (length and diameter of motor) as well as weight of the motor, power electronics and battery given the torque and rpm profile for the mission obtained from an aerodynamic performance model. The models developed in this work can be immediately applied to design G1UAS given the torque and speed requirements of the rotors/propellers, the operating voltage of the vehicle system, and certain high-level component specifications for the motor, electronic speed controller, and battery. The models can also be used to BLDC powertrains for small terrestrial or aquatic electric vehicles.
Student: Farid Saemi