Nice! This is more of what I'd like to see on HN.
Might be asking too much, but I'd also like to see a thread discussing the possible parts, schematics, and source code I could use to hack one of these together myself :) To start: what kind of rotors are those? Are they expensive?
The real trick is how they're getting them to calculate vectors. They're certainly not just remote controlled -- not unless they had an awful lot of takes of that 3" clearance shot -- so that raises the question, are they precalculating the vectors, or are they using some really advanced method to calculate them on-the-fly (so to speak)?
If they're precalculating, then the impressive thing here is the method they've developed to get these things to do tricks with rotors. If they're doing on-the-fly calculation, then I really want to know what kind of sensor they're using. I don't know of anything available on the hobbyist market with that kind of resolution and speed.
EDIT: Well, this is embarrassing. It spells out the answers to my questions right in the linked article. :-( Hooray for not paying attention.