I think that the one wheel with the screws was a gyroscope of sorts. I would guess that the biggest difficulty is height, and once they acheive that, they can just keep tweaking the setup until they can manage to keep in one place long enough. I'm sure the 4-rotor setup is optimal since both groups used it. However, I still wonder if you couldn't get by with one big rotor and a small counter-rotation rotor. It would have fewer moving parts, and be lighter. You might have to have them working on separate drives though, like feet for the big rotor, and hands for the small one. My read was that they had to stay at 3 meters for 1 minute.Maybe the trick is to hover just off the ground for the majority of the 60 seconds, then drive hard for the height as quick as possible to lessen any chance of drift.