As many of the other answers say, the current multicopters are very simple, mechanically: an electric motor directly coupled to a fixed-pitch propeller. Everyth

As many of the other answers say, the current multicopters are very simple, mechanically: an electric motor directly coupled to a fixed-pitch propeller. Everything is controlled by the amount of current the motors receive. Any other alternate arrangement means a more complex mechanical control: servos, gears, larger propellers, variable-pitch propellers... This makes them less reliable, harder to mend and more dangerous (that's one of the reason model helicopters never really caught on, even with modern electronic stabilizers - even a smaller 450-class blade can break bones if you hit it).