On the off chance you haven’t seen it yet, the UPenn GRASP Lab has just released yet another impressive video of their performance quadcopters. This time they’ve got a new “nano” version that’s smaller, lighter, and capable of flying in formation. It’s like synchronized swimming, but with more buzz:
Now as usual, the internet comments on this latest quadrotor development have largely consisted of “WOW!” and “Good heavens, they’ll kill us all!” But as for me, once I’d retracted my dropped jaw, I started trying to figure out how it all worked. Unfortunately, I haven’t found any real documentation on this project beyond the videos posted by PhD candidate Daniel Mellinger. I just might have to send him an email…
But never fear, I have at least discovered how they’re tracking the quadcopters. Did you notice those camera-like devices mounted along the walls? And those funky red ring-lights surrounding their lenses? Well those are VICON motion capture cameras:
These devices by themselves are quite impressive. Much like traditional video cameras, each of these units contains a sensor with a certain number of megapixels. However, VICON sensors are designed for fast frame rates (up to 2000fps), high resolution (up to 16MP, more than seven times the resolution of 1080p HD Video), and sensitivity to the red/infrared light emitted by their ring light strobes. Why red light? Well, these aren’t your typical video cameras. Their purpose isn’t to capture a full-color image, it’s to capture points of light coming from passive reflectors. In fact, what each camera sees looks like a star map of sorts. Once multiple cameras are setup and calibrated, sophisticated software can measure and track the position of each reflector in real time.
So in the video above, it appears that each quadcopter has at least two reflectors attached to its top surface. The perimeter cameras can then measure the position and orientation of each unit and relay that information to some kind of controlling computer. What I still don’t know is how the software distinguishes between each quadrotor. Perhaps VICON has reflectors which can be distinguised by the precise wavelength of light at which they reflect? Or maybe the computer is just smart enough to know that the same set of points represents a certain unit from one frame to the next?
I’m also wondering how each quadcopter is controlled. Some type of ZigBee wireless link perhaps? And does the main computer handle everything? I suspect there must be a certain amount of control embedded in each unit. Perhaps they’ve all got accelerometers and MEMS gyros keeping them straight and level. Still a lot of unanswered questions. But in the meantime, enjoy this video on a radically different use of the VICON technology:
The words “earthquake” and “ozone” are two terms you don’t often find used in the same sentence. Like “congress” and “effective”, or “health food” and “delicious.” And yet, MSNBC recently published an interesting news item whose title did just that: “Is ozone gas an earthquake precursor?”
As it turns out, when rocks such as basalt and granite are crushed, they produce substantial quantities of O3 – ozone gas. According to researchers at the University of Virginia, the amount of ozone released varied between 100ppb and 10ppm. To put that into perspective, the low end of this range is comparable to a very smoggy day in Los Angeles. The high end is one hundred times worse.
So I guess now we’ve got yet another reason to hate earthquakes: they split houses, swallow cars, and pollute the air. Although, perhaps if a quake destroyed enough cars this would offset the amount of ozone released. But I digress. The real question here is, “Can elevated ozone concentrations predict earthquakes?” Well according to researcher Catherine Dukes, no, not really: “It’s just a way to warn that the Earth is moving and something — an earthquake, or a landslide or something else — might follow.”
I suspect that any rock crushing action which produces ozone is also detectable via seismograph (although I’m just guessing). So perhaps this discovery isn’t so useful.
But crushed rocks producing ozone? This is still a rather strange phenomenon. Scientists are not yet certain of the precise mechanism at work here, but suspect that differences in electric charge between rock surfaces are the most likely cause. As you may know, lightning strikes are another natural means of ozone formation, particularly in the upper atmosphere, where ozone is more beneficial. While the strike itself does not directly form ozone, it breaks apart O2 into atomic oxygen, which may then recombine as O3 (see this PDF for details). Lightning also yields nitrogen oxides (also a popular automotive pollutant) which, in the presence of sunlight, react with other chemicals to form ozone. So the theory here is that differences in electric charge between the crushed rocks are producing small electrostatic arcs (miniature lightning strikes) which result in ozone gas.
Well, perhaps we should just chalk this up as another oddity of the universe – like X-ray-producing tape, or radioactive bananas… Still, it would interesting to know if there are preliminary tremors which aren’t detectable by seismographs but might be picked up by ozone detectors. Such predictions probably wouldn’t be too accurate though.