Jack, most of the swarming and flying robots, along with a lot of other robot research, seem to be funded by the military, usually DARPA. The one I mentioned also appears to be aimed at military applications.
Warren, I hear you. The huge advances in semiconductor shrinks and system-on-chip have made processors and memory capable of such feats, as well as big reductions in sensor size and rise in abilities because of MEMS technology.
Jack, wait 'til you see the much smaller flying bug in an upcoming robot slideshow: it's about the size of a quarter. I think that one will fit under the door. Not only that, but these are self-assembling: shades of Crichton!
It's funny how we used to think about how much memory it would take for such a task and know it was totally unrealistic. Now, it is reality. We have the memory and processing power. Now we just have to work out the "bugs."
The robots use some kind of continuously adjusted mapping functions to locate themselves in space and explore unknown environments, as Kumar states in the TED talk video:
http://www.ted.com/talks/vijay_kumar_robots_that_fly_and_cooperate.html I don't know if that technology is based on SLAM (Simultaneous Localization and Mapping), but I wouldn't be surprised. It's pretty popular for this type of application.
BTW, the robots in the story are the same robots from the U of PA GRASP Lab that play the James Bond theme in that video.
Hey, oldtimer8080, I did read PREY. It was very scary. In fact, I thought of that book when I saw the first video on these little robots, although I think they are also cool. I hadn't thought about the invasion of private property issues, good point. Your 'tude sounds like the 'tude of many of my neighbors up here in the mountains.
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