Robo-salamander goes swimming
Bot throws light on the evolution of walking.
It's yellow, modular, and can both walk and swim: it is Salamander robotica, the fruition of four years of research and one clever theory.
Auke Jan Ijspeert of the Swiss Federal Institute of Technology in Lausanne and his team made the robot to help test their theories on the evolution of walking: that famous moment when the first 'fish' scurried up onto land. The robotic creature helps to confirm their notion that the transition between swimming and walking can be quite simple.
The team used the amphibious salamander as a model for their study because it is reckoned to be very similar to the first ever land-walker.
The researchers knew that different gaits — in salamanders and people — are regulated by a part of the brain quite far from conscious control (imagine the agony of everyday walking if it had to be as deliberately planned as a newly learned dance).
And in 2003, the same team found that real salamanders could be made to switch from one gait to another simply by turning up electrical stimulation to a certain brain-stem area. The more stimulation, the faster the walking motion and the faster it wiggles side to side until, at a certain threshold, it would seamlessly switch into a faster, wave-like swimming motion.
Ijspeert figured that what he was dealing with were two 'central pattern generators' — two sets of nerve networks that would produce two different rhythms of movement. At low stimulation to one of these networks, the animal is prompted to walk at a slow speed, with the 'S' formed by its body simply bending one way and then the next. As the current increases, the animal speeds up, until the limbs 'top out'. At that point this nerve network shuts down and lets the second take over. The limbs are tucked in and, presto-chango, the animal starts swimming — with its 'S' shaped body moving in a travelling wave.
To test this hypothesis, Ijspeert decided to build his own, bright-yellow salamander. "Many salamanders have very funky colours," he explains.
The bot is built of a slinky chain of segments, each of which is independently powered. It is driven by command instructions made from a numerical model that Ijspeert's team built to describe a real salamander's behaviour. The result: a robot that gambols with a distinct salamandery vibe, and then breaks into a swim as the controls are turned up (see video).
"Some people say, why not give it some skin?" says Ijspeert. "I like the fact that it should seem natural because of its motion, not because of its skin."
Manny Azizi, a biomechanist at Brown University in Providence, Rhode Island, who did his dissertation on salamander locomotion, gives the bot the thumbs up. "I think the interesting thing is that the change happens instantly."
"They made some headway in multiple different disciplines: neurology, robotics and evolution," says Azizi.
Ijspeert says the robot's efficient amphibious gait might make it a candidate for search-and-rescue operations. Azizi's also got an idea for potential applications: "It's so cool. My kid would love to have one of these as a toy." No problem, says Ijspeert — but it would cost about $2,000 just for the parts.
- Ijspeert A. J., et al. Science, 315 . 1416 - 1420 (2007).