I wonder if someone has considered building a multicopter with a single motor.
My guess is that this could be achieved by using a two-face bevel gear and using carbon shafts to supply power to all rotors that should turn at same speed, flight control should be possible by varying pitch differently to each propeller
It might be some hard to get extreme differences in lift power for each rotor as would probably be a need for crazy pilots or under strong wind conditions, but I guess there could be advantageous in some points.
One single powerfull motor might weight is less than (3,4,6,8) regular ones
You can get weight closer to mass center reducing moment of inertia, making the whole frame more responsive.
One single speed controller,.. simpler wiring
the bad thing could be frictions in gears and shaft transmission.
I'd like to listen your opinion. (I'm rather new to drones and a complete dummie with regard to avionics, robotics and RC, so, if my idea is just a dumb's one, please, do not be too severe with me)
Regards.
Replies
My opinion is that once you start looking at this. Virtually throwing away all the advantages of a quadcopter (ie: simplicity) then you might as well just use a single rotor traditional helicopter. Then you gain back all of the advantages of a single rotor heli. The large diameter rotor is going to be more efficient than 4 small rotors powered by a motor of the same size.
However, just a comment on Brad's statement " no way any rotational inertia-limited control system can compete with the "right now" thrust delta of a pitch change" you must consider the time it takes to actually move a servo to change the pitch. I don't know how the time compares, but there is a time delay involved.
It's not a "dumb" question at all. Ultimately, the attributes of best hovering efficiency, control responsiveness, and forward flight performance all literally demand variable pitch blades. There is no way any rotational inertia-limited control system can compete with the "right now" thrust delta of a pitch change. However, the added mechanical complexity and localized aerodynamic problems can be rather daunting.
At first glance, having one central motor might have an inertial advantage as you say. I think the transmission losses might very well wash out any possible efficiency gains, and you will still end up with quite a bit of hardware at the thrust arm tips for power transmission, mounting shaft bearings, etc. Direct-drive smaller motors still seem like the most straightforward approach.
Ultimately, variable-pitch blades are on the eCopter(tm) roadmap, likely on a second or third production version.