Walking tall

Scientists in France and Switzerland have developed a robot in order to test a biological theory. Researchers at the Ecole Polytechnic Federale de Lausanne (EPFL) in Switzerland, and Inserm and Bordeaux University in France, had developed a numerical model of a salamander’s spinal cord – to try and prove that the neurons it uses for swimming can also be used in walking. It has implemented the model in a robotic salamander, which it calls the Salmandra robotica. The robot changes its speed and gait in response to simple electrical signals, suggesting that the distributed neural system in the spinal cord holds the key to vertebrates’ complex locomotor capabilities. The same team has also developed the ‘Amphibot’ – an ambhibious ‘snake robot’. While the biological theory is of limited interest to engineers, it shows how biology can help in the design of robot controllers. It could also lead to new types of amphibious robot that mimic the salamander in its ability to both swim and walk. Professor Auke Ijspeert, head of the Biologically Inspired Robots Group (Birg) at EPFL, said: “Nature has found a nice way of making a sophisticated circuit in the spinal cord and then controlling the muscles from there. It’s a fantastic solution for coordinating multiple degrees of freedom in a simple, distributed way.” The researchers say their work could lead to robots that change their speed, direction and gait based on simple remote signals – which could be useful in search and rescue operations, for example. According to EFPL: “To our knowledge, it is the first robot that combines the three modes of locomotion – swimming, serpentine crawling and walking.” It is not only the robot itself that is modelled on biology. The locomotion control system model actually simulates a central pattern generator (CPG) – a circuit that can produce co-ordinated patterns of rhythmic neural activity. In the robot, it is implemented as a system of coupled non-linear oscillators running on a microcontroller. Simple drive signals are sent wirelessly from a laptop to the robot in order to modulate its movements, mimicking the way in which the brain sends simple signals to the spinal cord in order to initiate and modulate locomotion. The robot is driven by 10 DC motors. These actuate six hinge joints for the spine and four rotational joints for the limbs. The robot’s limbs move in continuous rotation – which does not match exactly with the original – while the spine produces lateral motion. It has been tested swimming in Lake Geneva. The researchers found that low levels of stimulation produced the slower walking gait, but this switched to the faster swimming gait at a higher level of stimulation. Robots are increasingly used to test biological hypotheses, say the researchers – who argue that their work has extended understanding of robotics. “There is currently no well-established methodology for controlling the locomotion of robots with multiple degrees of freedom – in particular for non-steady-state locomotion in complex environments,” they say in their latest paper, which appeared in the 9 March 2007 issue of Science. www.bordeaux.inserm.fr/ www.epfl.ch/