Unmanned Systems Technology 028 | ecoSUB Robotics AUVs I ECUs focus I Space vehicles insight I AMZ Driverless gotthard I InterDrone 2019 report I ATI WAM 167-BB I Video systems focus I Aerdron HL4 Herculift

38 Focus | Engine control units Ongoing advances in CAD software mean that such physical, environmental and EM forces acting on components can be modelled simultaneously. That will simulate their impacts on the mechanical and electrical robustness of the ECU, making designing for the operating environment faster and more accurate. Also, considerations such as the expected unit life, expected design support and the required production volumes over a given period will be required – along with agreement on a price point and cost priorities. The physical requirements would then need to be defined, including constraints for mass, volume, dimensions and the intended installation location. Naturally, the architecture of the engine needs to be described in detail. Not only should the many sensor inputs and actuator outputs that ECUs are primarily used to handle be made available, so should the operational profiles for speed, power, torque, fuel consumption rates and propeller (or other load) characteristics. Diagnostics requirements must be established as well. As mentioned, onboard diagnostics are vital for handling engine faults during flight for either the engine or operator to react appropriately. Also, ground-based diagnostics tools can be designed to make UAV maintenance faster and more effective, by identifying the nature and optimal solutions for engine problems before communicating them to technicians. Similarly, the presence of systems for tracking operating hours and the engine power levels being used can be helpful when engine manufacturers issue warranties to UAV manufacturers and operators. These will record closely whether a customer was using the engine in a responsible or reckless way, so the kinds of data to be logged on an ECU should be discussed. Lastly, software considerations such as the target language and interfacing, as well as the quality assurance level (such as DO-178) must be weighed up. As the degree of data, analytics and software functionality to be handled by ECUs steadily increases, growth margins may need to be established for memory and processing, to offset the need to replace microprocessors or SD cards in the future. Caution should also be taken in other ways when designing an ECU. For example, as mentioned, there have been great advances and new releases in key computing technologies such as multi- core processors, and it can be tempting to ask to have these installed in a next- generation ECU to provide a step increase in software speeds and functionalities. However, it can take years for fundamental problems with new hardware to be discovered. It’s a perennial issue, and is the main reason why research aircraft testing new equipment often go to the ‘extreme’ of using technologies that are many decades old for their other onboard systems. For example, a new CPU design could start emitting unexpectedly high heat or EM noise during high processing loads after 1000 running hours, significantly shortening the lifecycle of its ECU. Adding too many components and too much protection can also run against the need to cut weight on UAVs. Determining what an end-user does not need can help establish which processors, resistors, connectors, heat sinks and so on can be removed. Cutting just 25-30 g from an ECU can enable a significant payload camera upgrade for a UAV. Issue of redundancy Some ECUs will not incorporate any significant degree of redundancy, and will therefore bear a lot of single points of failure, such as having only one crank speed sensor or cylinder head temperature sensor. That means there are a lot of pathways and wires that could cause the unmanned vehicle to be lost if it’s damaged. As UAVs handle increasingly harsh environments and expensive payloads, this lack of redundancy becomes more likely to lead to problems. Checks should also be made for all the important functions that are unique to flight requirements. These could include ensuring that the flight controller does not close the throttle in response to engine heat if the UAV is cooling too quickly during a descent, or something simpler such as opening the throttle proportionally with altitude (which nonetheless might not occur to automotive engineers). And when integrating an ECU into an engine, it is common to calibrate it with a propeller mounted, particularly among users and manufacturers of small fuel- injected engines in the UAV realm. However, changes in the propeller – if it’s swapped out or receives minor damage from gravel or bumps on October/November 2019 | Unmanned Systems Technology CAD software can be used for modelling the structural and electrical robustness of ECUs in harsh environments (Courtesy of Orbital UAV)