Catchbot Catches Balls Like You Do, Only Worse

Writing by Evan Ackerman on Monday, 29 of September , 2008 at 1:25 am

Getting robots to throw stuff like bowling balls and basketballs isn’t a walk in the park, but it’s much easier than the other end of things: getting robots to catch. Catching a moving object is (depending how sporty you are) either deceptively simple or deceptively difficult… You’re moving, the object is moving, and your brain has to figure out where the twain shall meet. Robots are good at math, but you need a lot of computer power and a gaggle of high speed cameras to figure out exactly where something like a ball is going to land.

So how do humans, who generally suck at doing complex math and playing sports at the same time, get it to work so well? For that matter, how do animals pull it off? Turns out that both humans and animals have just come up with a clever generic strategy that gets the job done, and Michael McBeath (an engineering professor at ASU) and Thomas Sugar (a psychology professor) have figured it out. Read how it works, after the jump.

Perception really is everything, when it comes to catching a baseball. In order to catch a fly ball, the McBeath-Sugar team found that a human outfielder first sees the ball as it moves up in the air. He then instinctively moves relative to the ball to keep the ball’s image moving at a constant rate. Maintaining a constant change in visual angle keeps the fielder on track to catch the ball.

When a baseball is hit up into the air, the outfielder will instinctively move to be under where it is headed simply by keeping the image of the ball continually rising, even while the ball physically descends. If the image of the ball starts to curve toward the ground, the fielder runs so as to straighten the curved trajectory back up.

“As the ball moves, the fielder moves to the spot that keeps the ball angle rising,” McBeath says.

“We found that insects, birds, bats, and dogs all appear to behave the same way,” McBeath explains. “It seems to be a generic strategy. No matter where a target is coming from, you try to control the relationship between you and the target. If you can see and keep the target moving at a constant speed and pretty much in a straight direction relative to yourself, then interception is guaranteed.”

“You don’t need complex calculations to solve these problems,” says McBeath, who has undergraduate and graduate degrees in electrical engineering, as well as psychology. “It’s simple control theory. The idea is to keep the ball image moving up and over at a constant rate.”

It really is that simple, apparently… Or almost that simple. The researchers have developed a little robot called Catchbot that uses these rules to chase ground balls. So far, it’s fielding about 75%, which is not particularly impressive, so there are obviously some ball catching tricks missing somewhere. But the idea is a crucial one: the answer to catching a ball is not massive computing power and complicated hardware. Rather, it’s a simple idea based on biological principles. Extend this idea, and you might end up with a bot that’s better able to dynamically navigate around complex environments using purely perceptual data rather than terraquads of maps, rules, and code.

If you feel that all that was a bit dry, I don’t blame you, even if it is pretty cool. C’mon, it’s cool! But I feel your pain, so here’s a video (admittedly lame, but a video nonetheless) of Catchbot catching something.

VIA [ ASU ]

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Category: Biorobotics, Research

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