By Gregory Mone
Posted 07.23.2007 at 3:34 pm 0 Comments
Garth Stewart, a 24-year-old Iraq veteran, took his first normal steps since losing part of his leg in the war, thanks to a prosthetic ankle that operates like the real thing. Most foot prostheses work through simple springs, but this new robo-ankle, developed at MITs Media Lab, has a battery-powered motor, too. When Stewart walks, the energy he exerts is stored in a series of motor-backed springs. Then, when he pushes off with his prosthetic foot, this energy is released, and he moves forward. The motors give this motion more power, and ultimately allow Stewart to expend less energy with each step than he would while wearing a standard prosthetic foot. The robo-ankle also leads to a more natural, fluid gait. MITs Hugh Herr, who led the research team, is also an amputee. He tested the invention himself, and compares it to walking on a moving sidewalk in the airport. The device may be commercially available within a year.—Gregory Mone
Ordinarily, driving is pretty straightforward: You just point the wheels and go. But piloting an aircraft is trickier, because you not only must deal with complexities like the potential for traffic above and below the plane, but your roadway—the air—moves. Until it’s time to land, of course. Seamlessly transitioning from sky to asphalt is the most difficult thing a pilot regularly has to execute, especially when winds are strong and blowing from side to side (as in the crosswind landing featured in this video). But it’s easy enough to understand what a pilot should do in such circumstances, even if you’re too freaked out to ever in a million years attempt to do it yourself. All you need are vectors.
A vector describes how something moves; picture it as an arrow. The vector’s length describes how fast the thing is moving, and its direction tells you which way it’s going. If you threw a baseball straight up in the air, the vector that described its movement would start out long—the ball’s going fast—and pointed toward the sky. Then the vector would shorten as the ball slowed and, at the top of its arc, would flip downward and grow long again as the ball fell.
If an object is moving in or on a medium that’s also moving—a person on a moving sidewalk, a swimmer in water, a plane in the sky—you figure out how the two will move together by taking the vector for the object and the vector for the medium and joining them together head-to-tail.
In our example, the wind is whipping from left to right, so its vector points that way. For the plane to move straight ahead, its vector must cancel out the left-to-right vector of the wind. That means it has to point a little to the left, or into the wind.
Of course, once the plane hits the ground, it had better be pointing in the direction it’s moving. That’s why the pilot has to straighten the plane out at the last second. If he did it any earlier, the wind would start to pull the plane to the right; if he did it any later, the plane would hit the tarmac sideways and flip over onto its wing. And you thought parallel parking hard. —Michael Moyer
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.