Unmanned Systems Technology 025 | iXblue DriX I Maintenance I UGVs I IDEX 2019 I Planck Aero Shearwater I Sky Power hybrid system I Delph Dynamics RH4 I GCSs I StreetDrone Twizy I Oceanology Americas 2019

64 April/May 2019 | Unmanned Systems Technology Sky Power has developed its own ECU and ignition system for closer control of the hardware and software than could be achieved by relying on any external supplier. It has designed them with the intention of having a large degree of commonality and interoperability between the ECUs of their different engines, irrespective of hardware differences between the engines. As well as a 32-bit controller, the microprocessor powering Sky Power’s ECU030 comes with 512 kbytes of storage memory, 96 kbytes of RAM, and works on a 72 MHz pulse frequency across a temperature range of -25 to +105 C. The key control inputs are sensor data on crankshaft speed, throttle valve angle, engine temperature, air temperature, water temperature, exhaust gas temperature and air pressure. These enable control outputs for fuel injection, ignition, servo motors and the power management system. In all, there are 24 signal contacts and eight power contacts. With all information flowing through the ECU at a single point, the UAV manufacturer integrating Sky Power’s engine can connect its flight controller with a single comms channel to the ECU to receive sensor data from the powertrain during flight. Also, a technician can connect their laptop to the ECU to have all that information present in the calibration software. The ECU software has been written in-house using C++. Sky Power has chosen not to implement a throttle- focused control system in the ECU, viewing this as too simple an approach. Instead, the software has been modelled around controlling the engine’s torque. “Torque depends on throttle position, which is not linear – and torque also depends on the speed and the load of the engine,” explains Walter Seidl, the company’s chief engineer. “To implement a torque management system, we need to be able to understand the range of engine speeds and loads the customer wants, from 0% to 100%, and we can generate a map for torque values in Nm, as well as percentage values for the end-user to select using the flight controller.” The ECU’s injection control varies between engines. Sky Power’s air- cooled two-strokes have fuelling determined by air temperature, cylinder temperature, air pressure (denoting altitude) and exhaust temperature. If, for example, an unmanned helicopter is hovering and generating a lot of heat in its engine, cooling is first initiated by increasing the injection rate, and subsequently the throttle and speed can be automatically reduced if the engine temperature still doesn’t drop. For Sky Power’s water/oil-cooled rotary, fuelling is lambda-controlled using a Bosch Wideband 4.9 LSU sensor. However, a standard throttle/ speed-governed injection control is also embedded within the software to add redundancy. “That means that if we have an error reading from one sensor, we can use this model to calculate what a standard value from the sensor should be, at that time and within the context of the rest of the data being received,” Seidl explains. The ECU’s software architecture Sky Power ECU and ignition The ECU030 is Sky Power’s standard engine management solution, and is used across the company’s range of two-stroke engines, with just minor variations for ECUs for other engine types Map of the SP-180 SRE’s torque in Nm, according to load and speed