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

68 E ngine control units (ECUs) are embedded computers containing microcontrollers that manage all the devices attached to an engine that affect its performance. To a great extent, ECUs are shaped by the engines they are used to control. Most UAVs between the small electric aircraft and machines large enough to need engines developed for manned aircraft have piston or rotary engines with ratings of between a few horsepower and around 120 hp. Within that broad category are two-stroke and four-stroke spark ignition and compression ignition engines, most with one or two cylinders. They run on a variety of fuels fed to them either by carburettors or, increasingly, electronic fuel injection systems. They also feature a range of sensors that measure important parameters such as engine rpm, throttle position, air and liquid temperatures and pressures, for example. All these subsystems affect the computer hardware and software, input and output (I/O) arrangements and the analogue electronic components ECUs need, which in turn drive their complexity, size, weight, power consumption and cost. Automotive experience Developers can draw on experience, hardware and software from sectors of the automotive industry including utilitarian scooters, high-performance racing vehicles and the emissions and fuel consumption-focused realm of roadcars. UAV engines are rarely as complicated as automotive engines, so ECUs based on automotive technology can be pared down for UAV applications. Taking the top off an ECU would reveal several silicon chips, at least one of which would be a microprocessor of the same type or even the same make and model as that found in many automotive ECUs, and which runs the high-level engine control software. This would typically be accompanied by a number of ASIC chips that carry out lower-level tasks, a lot of interface circuitry and I/O, and many discrete electronic components. A subset of these discrete electronic components is the group of analogue devices used for their ability to handle the higher currents needed to switch on and off (‘drive’) the electromechanical components in the engine. Peter Donaldson explains the factors that dictate ECU design Chain of command October/November 2017 | Unmanned Systems Technology