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98 Focus | ECUs sensors such as the ECU’s I/Os, and the degree of calibration and maintenance needed to prevent faults in the engine management. Questions must also be asked of the autonomous platform itself. Whether it is a helicopter, multi-rotor, STOL fixed-wing or VTOL-transitioning fixed-wing system gives critical information about the power bands and curves that will be needed over the flight envelope, as well as other variables. Once high-level requirements such as these are made clear, low-level requirements can be tackled, including ECU hardware specifics such as connector design, pin layouts and enclosure ruggedness. Wider design details can also be defined, such as the addition of sensors for intake air temperature, main bearing temperature and other factors that, while not critical for the core functioning of the engine, can still be important for overall health monitoring, particularly as organisations look to manage their running costs better. Most new UAV customers approaching ECU manufacturers rarely wish to go through all of that; more often than not, they will merely ask for a COTS ECU design. Almost without fail, however, they return to the manufacturer with a list of adjustments – some considerable, some minor, and sometimes returning more than once – but by and large, the process plays out as described. Given how many different autonomous aircraft there are, and how different their use-cases are, there is no one-size- fits-all ECU design. From a hardware standpoint, however, most ECU manufacturers have their basic board architectures well-established in-house. These architectures are now quite stable technologically – as noted, the only major factors driving change are supply chain shortages. Adjustments in light of these can be regarded as synonymous with the never-ending push towards ‘design for manufacturing’ – that is, tweaking designs to keep manufacturing going with fewer materials to hand. Designs can therefore be reconfigured to handle different configurations of spark plugs, injectors, servos and less common ancillary systems such as forced induction componentry, heavy-fuel heaters and engine data links. Once the complete list of sensors, processors and connectors has been defined, the manufacturer can draw up electric and electronic schematics of what the eventual PCB will look like, first in 2D wiring diagrams and eventually in 3D CAD. Simulation and testing Once in CAD, the ECU can be simulated for how it will function – and the way in which it might fail – amid the severe heat and vibration it experiences by being so near the engine. Design simulations nowadays also investigate the potential effects of shock, such as physical impacts from engine knocking or high-speed transients, or electrical shocks given the increasing outputs of electric power that users these days want from their engines. For similar reasons, detailed and accurate simulations of EMI are extremely valuable, as ECUs can be engineered to function with resilience against interference from motor/generators, servos and the electronics in their vicinity, by carefully housing processors, potting connectors and so on. In addition to simulating issues in CAD, high-end ECU manufacturers will directly simulate the kinds of exceptions and errors that software can be prone to on a day-to-day basis to test that the ECU reacts correctly. Some will for instance directly command a ‘divide by zero’ as part of their routine software testing of the processor, to see if the system can trap the exception, reset, and report accurately on everything that happened, from timing to the nature of the invalid operation. On top of running all kinds of different functions, applying them to new ECUs across the gamut of physical trials is more critical than ever. With designs changing to compensate for component shortages, these new architectures must be checked extensively to ensure their outputs match those of their predecessors and suffer no loss in performance. Bench testing and engine cycling are the most obvious and hands-on ways of inspecting how the ECU performs April/May 2022 | Unmanned Systems Technology Extensive high-fidelity tests of heat, shock, EMI and more are critical to eliminating failure modes before batch production and delivery (Courtesy of Orbital UAV)