I have a large drone and I am contemplating going forward on an earlier idea to build a very lightweight generator module to replace approximately 6kg of batteries. The components are relatively few. There needs to be a very small fuel driven engine ( I am leaning toward the Honda mini 35cc four stroke), a 350 kV, brushless motor-cum generator, three phase rectification, 30V, LARGE electrolytics as smoothing capacitors feeding thru a diode into a 4s lipo at a boot strapped ~15V output. 800W would be just about right.
The package design is still too heavy. The appeal of the Honda is the completeness and cost. By removing the cowling, the clutch and milling away as much of the "unnecessary" aluminum as possible, it is probably still going to be pretty heavy. I don't know enough about the RC motor market to build up the equivalent fuel tank, throttle, muffler etc to produce a lighter motor solution. Nitro fuel is way less efficient and so, 2 or 4 stroke gas is more attractive.
The capacitor size depends on how much ripple would be acceptable to continuously "top off" the lipo and maintain the 15V charge and produce a further smoothing of the 15V to the ESCs. This will require some bench testing.
I am hoping to avoid a throttle control feedback, by allowing the motor to run wide open and under the design load, produce the required voltage by selecting the best KV rating for the generator. This is unless a simple throttle feed back loop is simpler than I fear. The lipo would provide the additional power when maneuvering as the draw down of its voltage under increasing load would pull additional amps from the battery.
Exotic sources such hydrogen fuel cells are just not practical...yet. So, I don't want to go there. I actually want to build this thing, now.
Any ideas or suggestions?