UAVHE RW1 rotary | Dossier triple-rotor versions of the RW1 engines someday. A shaft designed three times longer would naturally need extra bearings to hold it steady,” Bogdanov adds. Gearbox and propeller While the RW1-79 is not designed for propeller output, the RW1-300 integrates a two-stage gearbox with a wet centrifugal clutch. Typically, this does not engage until at least 3000 rpm at the eccentric shaft, and the standard reduction ratio is 1:3.2, but the engagement point can be preset on the ground as per user requirements. The oil bath is sealed. Sensors for temperature, viscosity and metal shavings, installed at ports around the gearbox housing, instruct the user on oil replacements rather than relying on a rough hourly count. “Each cog is CNC-milled from a proprietary material on our DMG MORI CTX machine, and given thermal and chemical surface treatments, such that the gearbox produces almost no noise and does not represent a key point of failure for the 300 engine. We’ve yet to suffer a gearbox fault in any test, including lubrication, overheating or overloading failures,” Bogdanov says. “We’ve oversized the bearings and some of the gears, but that makes for a very rigid structure. Outside of the housing, we’ve designed quite large fins so that the front functions as a radiator for the gear oil.” An electric variable-pitch propeller is typically installed on the gearbox’s output shaft, with a 52° swing range, and a transfer time of less than three seconds for the blades to move from their start to end positions at maximum load. Generator In both the RW1-79 and RW1-300, the 11 kW motor-generator is directly driven off the back of the eccentric shaft. The system is a BLDC outrunner design, constructed in-house. “As well as starting the engine from a dedicated, 5 A starter battery, and providing power for the main batteries and subsystems, it also functions as a smart flywheel on the 300,” Bogdanov says. “As some will already know, Wankels’ torque curves over shaft rotations are uneven – torque rises quickly at the ‘power stroke’ right after combustion but drops during the compression right before that. “To compensate, we measure the revolution timing via a crank position sensor and engage the generator following combustion, drawing slightly from the power and torque to charge a bank of supercapacitors. Then, when the power stroke ends and we’re at a trough in the torque curve, we release the load from the generator, switch it to a motor mode, and return some of the stored energy back to the motor and hence to the shaft. “That flattens out the torque output, relieving a lot of stress and vibration from the gearbox, the propeller and other components. Our power management includes torque balancing even if the enduser chooses to use the hybrid system for prolonged boost power to the propeller; energy drawn by the motor to power the shaft will be less pronounced during the power stroke, and more pronounced during intake and compression.” UAVHE’s smart flywheel technology was originally developed for two-stroke paramotor engines to minimise vibrations transmitted through to the paramotorists’ backs, while the high power and hybrid aspects of the technology were first innovated for jet skiing. Power management “On top of those features drawn from our motorsport engines, we’ve further configured our electrical output 77 Uncrewed Systems Technology | April/May 2024 An exploded-view diagram of the RW1-79 The gearbox produces almost no noise. We’ve yet to suffer a gearbox fault in any test, including lubrication, overheating or overloading failures
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