Unmanned Systems Technology 016 | Hydromea Vertex AUV | Power management systems | Unmanned Space Vehicles | Continental CD-155 turbodiesel | Swift 020 UAV | ECUs | DSEI 2017 Show report

72 development of the core technologies in ECUs, many automotive systems have become large and complicated. This is partly because they control larger and more complicated engines – a V8, for example, might have eight fuel injectors and therefore need the same number of injector drivers and I/O pins. Automotive ECUs are also expected to run a wide range of functions such as variable valve timing, anti-lock braking systems and traction control, for example, which UAVs don’t need of course. Seeking simplicity A practical approach to these problems is to take the core of an automotive ECU that has been stripped of all the driver circuitry not needed by the intended application to create a smaller, simpler and cheaper solution. One manufacturer tells us that the core of its ECU can potentially run thousands of different engine types, but it removes some of the electronic hardware so that it has only two injector drivers, for example, and associated I/O to run single- and twin-cylinder engines. The result is an ECU that is potentially general purpose, but its drivers and I/O are pared down to suit the UAV application. The microprocessors/microcontrollers at the heart of UAV ECUs are mass- produced general-purpose devices. Developers have a wide variety to choose from, including the latest multi- core processors, although for the sake of simplicity UAV ECUs typically use processors that are one or two generations older. It seems more than likely that many UAV ECUs will exploit multi-core processors as, in addition to higher processing speeds, they can provide better data logging capabilities and have the capacity to support the additional control loops that newer engine systems might need. They also allow several high-priority tasks to be executed in parallel, and allow the ECU to handle more complex algorithms with greater computation and memory needs; safety-critical operations can also take advantage of them. Processor issues While multi-core processors are often used in the watchdog role for reliability in automotive applications, this is not typically a requirement for a UAV ECU, although that could change. For developers of ECUs for small, relatively low-speed engines, the exciting aspect of new and more capable processors is that they are usually smaller, cheaper and use less power. One developer makes a point of avoiding multi-core processors, sticking with tried and tested single-core devices. If more processing power is needed, it will add another processor and connect them using a CAN or serial peripheral interface bus. This separation of responsibilities provides a degree of redundancy, the developer argues. Illustrating a different approach, another developer intends to consolidate the functions run by two microcontrollers on its ECU. Currently, one processor runs the core engine functions of fuel injection and ignition timing, while the other runs UAV-specific telemetry and the fuel pump. In future, these will be run by one microcontroller to reduce the cost and complexity as it ramps up its production volumes. More peripherals Although UAV engines are much simpler than their automotive cousins, and therefore make fewer demands on their ECUs, the trend is towards UAV engine ECUs controlling more parameters and devices. These devices include variable-pitch propellers, fuel pumps and throttle valves. There is also a growing demand for feedback on the status of the engine and its ancillaries, again including fuel pumps plus other items such as sensors, actuators, ignition modules and cooling flaps. October/November 2017 | Unmanned Systems Technology Focus | Engine control units ECU configuration is dictated largely by the design of the engine and the sensors that provide feedback to the processor (Courtesy of Power4Flight)