86 power connectors. This was completed in November 2022, and at the time of writing the company was carrying out endurance testing and preparing for flight testing to verify its performance targets and mature the complete system. “About 50 hours of endurance testing have been completed, to prove-out the EFT-Hybrid-1x’s long-term performance capabilities, identify failure points and optimise or mitigate them to eventually identify and guarantee a minimum TBO,” Kahnert explains. “It also allows us to work through our maintenance routines and see how well the packaging and integration lend themselves to quick detachment and replacement of parts.” EFT is also on the lookout for suitable pilot customers who they can engage with to develop versions of the Hybrid1x that are optimised for real-world use cases. It anticipates that the UAV market is more likely to want small batches of customised powertrains than bulk orders of COTS systems. Hybrid Control Unit The HCU – also called the EFT-HCU-1x – is the master controller for EFT’s hybrid powertrain. Much like most of the ECUs we have previously discussed, it is the central receiving point for all the data collected from the sensors across the EFT-Hybrid-1x. Based on the processed readings, it transmits commands to control vital powertrain subsystems to achieve performance and safety targets, as needed by its own mapping and by the autopilot (with which it maintains a constant interface). Considerable work has also gone into tailoring the HCU’s firmware for calibrating it to the power requirements of the customer’s UAV platform, given that different UAVs will have different arrangements of motors, motor controllers, flight controllers and connections. When the HCU initialises it will therefore run through a number of pre-processing checks on subsystems such as autopilots, ESCs and electric rotors, and calibrate or even rewrite its software modules to ensure the engine, alternator, PMU, battery and cooling system all run in a way that is tuned to the flight and power profiles of that particular UAV. “This includes things like appraising performance and health data from the UAV manufacturer’s records to set alarms for platform-specific motor winding temperature limits, maybe with escalating levels of alarms so they can know the degree of urgency with which maintenance is needed, or know when landing immediately is a safety imperative,” Kahnert says. The master controller principally had to be capable of communicating with the sensors and lower-level controllers throughout the EFT-Hybrid-1x. “Typically, the comms between the HCU and the UAV’s flight controller is over CAN 2.0b, with our own suggestions for layouts and content of messages combined with any additional information packets that the end-user wants,” Kahnert says. “The BMS is then typically also connected via CAN, and the PMU outputs data over RS-232.” Interfaces for UART, SPI, I2C, PWM and more are also available on the HCU, along with an SD card for logging data at a high rate from incoming sensor connections, for real-time monitoring and long-term maintenance tracking. The sensors include seven hightemperature thermocouples across the engine for measuring temperature across the cylinders, heads, exhaust June/July 2023 | Uncrewed Systems Technology The alternator is a 203 mm-diameter systemwith 18 slots in the stator and 22 magnets in the rotor (Courtesy of Acutronic) The alternator has a commercial insulation system rated for heat levels up to 200 oC, which makes it safe for the electric machine to run with the engine
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