Unmanned Systems Technology 010 | nuTonomy driverless taxi | Embedded computing | HFE International marine powertrain | Space vehicles | Performance monitoring | Commercial UAV Show Asia report

52 is the triggering for a Hall effect engine speed sensor, while the starter motor/ generator is belt-driven from the flywheel. Whenever the crankshaft is turning, so are both the rotor of the starter motor/ generator and the water jet impeller; neither is clutched. When propulsion is not required but electrical power generation is, the engine is run at idle, which doesn’t provide enough power for the water jet impeller to move the buoy but does charge the batteries. Starting the engine An alarm sounds before the engine automatically starts, as a warning for the user. The starter motor/generator is a 200 W Maxon dc motor driven at a 1.5:1 gear ratio and electronically controlled via a proprietary circuit card to operate either as a starter motor or a generator. The engine starting speed is 1300 rpm. The ability to start and stop the engine automatically, sometimes repeatedly, was a major consideration, as West explains. “The autopilot gives a high and a low signal: high means the engine needs to be running, while low means it has to be off. We had to do all the engine control beyond that. “We had to make sure the engine would start when the autopilot gives a high signal, and would then release the starter and convert over to power generation when it is running. I think that is one of the cleverer aspects of the system, that it knows when it is not running and how to restart itself based on closed-loop control from the engine control module.” West says a fully autonomous system requires that any fault is “automatically detected and corrected” immediately, without user input. “For example, if the buoy were to roll over in a wave and the engine stalls, the system must be able to detect that the engine is off and restart automatically. “Older systems require the vehicle’s operator to engage the starter from the ground station if they detect that the engine is off. This H70 platform is designed to engage the engine when the enable signal is held high; no other input is required. “Our starting system will automatically start the engine, detect when the engine is running and disengage the starter, and automatically switch to generator mode. If the rpm drops to zero, the system reverts to start mode and restarts the engine. “The engine management system provides rpm data to the generator control board. The system uses this information to determine when to stop running the starter and switch to power generation mode.” One of the H70’s commissioning October/November 2016 | Unmanned Systems Technology Dossier | HFE H70 marine powertrain The H70-powered autonomous buoy sets off on a mission The HFE lower crankcase includes this segment that incorporates the mounts that tie it into the buoy