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34 T he dynamics of electric lift motors and servo motors seem straightforward at first glance: the former spin in a given direction, the latter move back and forth. However, a huge amount of hardware architecture and software programming goes into designing precise, energy-efficient motor controllers – or electronic speed controllers (ESCs) – for achieving consistent and sustained motor torque output. Until the early 2010s, UAV manufacturers were largely stuck with using hobby-grade ESCs, such as those for RC applications and consumer UAVs. These often suffered from issues such as poor transient response and low power density, and had mean times between failures (MTBFs) as low as 50 hours. In the past five years though there has been a surge in the availability of highly engineered motor controllers that can cater for small but high-quality commercial and military multi-rotors, for which failures of any kind – let alone acceptance of short MTBFs – are not an option. Also, advances in technologies for EVs and the increasing rate of hybridisation among UAV engine companies have given rise to new components and design topologies that are well-suited to the newer generations of larger, long- endurance, heavy-lifting UAVs as well as urban air mobility (UAM) vehicles. These increasingly use motors built for Rory Jackson looks at the technologies and design approaches enabling greater power and reliability in modern motor controllers Speed is of the essence Motor controllers for UAVs have to strike a careful balance between power transistors, capacitors, thermal management, software programming and other critical components (Courtesy of Currawong Engineering) December/January 2021 | Unmanned Systems Technology