While the vast majority of UAVs are powered by lithium-type batteries (LiPo, Li- ion, LiCo, etc.), the choice of such batteries ultimately limits flight time because of their characteristically low energy density. In fact, the most advanced commercially available heavy-lift UAVs provide less than one hour of flight time.1 More energy-dense, gas-powered drones exist, but their performance hinges on multiple independent combustion engines and a system of pulleys to replace the brushless motors.2 To meet the 3 hour flight time demanded by our proposed heavy-lift UAV for the Shell Ocean Discovery XPRIZE, we propose a hybrid gas- electric system that provides DC power by using a 3-phase, full-wave bridge rectifier to convert the AC power supplied by a generator. The generator is coupled to combustion engine, whose shaft speed is determined by servo- controlled throttle and choke valves, thereby being able to produce instantaneous power to meet demand as needed. Here, we present a compact generator assembly that can be controlled with a simple electromechanical architecture. We implemented this hybrid power generation scheme with a benchtop model and demonstrate that it can meet the consumption needs of the heavy-lift UAV.
NOTE: As a word of caution, the current being driven through the rectifier is pretty insane - if you are attempting a similar project, please use proper ESD equipment and grounding. Once the engine was started, we physically disconnected the ESC as to not destroy it. High power electronics work should be well-supervised - we had a safety checklist to reduce the possibility that we would be harmed. Safety is the most important thing in all projects - please do be careful!