20-legged robot moves effortlessly through terrain
Robot Argus has 20 legs. This allows it to move in any direction immediately. According to the researchers, this is almost optimal.
(Image: Duke Engineering/Screenshot)
Scientists at Duke University's General Robotics Lab have developed a rather unusual locomotion concept for robots and built a robot with 20 telescopic legs. This allows the robot to move uniformly. It can also change its direction of movement immediately, transport loads, and cope with almost any terrain formation.
The researchers determined the robot's design through a simulation of more than 1500 robot configurations to obtain a robot that could move optimally. Appearance was not to play a role. The result is a robot without a front or back, as detailed in the study “Extreme Dynamic Symmetry Enables Omnidirectional and Multifunctional Robots“, which was published in Science Robotics.
The robot, named Argus, has a spherical structure. A total of 20 modular telescopic legs extend radially from a central dodecahedron-shaped torso. The body thus has twelve pentagonal faces from which the legs emerge. Each leg end is equipped with a depth camera, which the robot uses to perceive its surroundings. By using a uniform dodecahedron as the central body, the 20 legs are arranged evenly around it. This ensures optimal visibility in all directions at all times through the cameras.
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The individual legs are extended and retracted depending on the desired direction, pushing the robot more by rolling than walking in the respective direction. As a result, due to its symmetry, the robot moves relatively precisely – even on sand and wet surfaces. It can climb vertically between walls and carry or push loads of up to 4.5 kg. It stabilizes itself. Additionally, the robot can overcome obstacles up to a height of about 13 cm.
“Watching Argus move is unlike watching any other robot we've worked with,” says Jiaxun Liu, co-author and doctoral student at Duke University's General Robotics Lab. “The first time we saw it navigate among trees and rough terrain, even under heavy collisions, we knew this was something different.”
Dynamic Isotropy
The researchers wanted to determine how uniformly Argus could accelerate its center of mass in any direction. To do this, they developed a mathematically derived design principle they call “dynamic isotropy.” Dynamic isotropy can have a value between 0 and 1. The value 1 represents the theoretical maximum with optimal acceleration. Modern robots – whether on two or four legs – achieve a value of less than 0.6.
In the movement tests, however, Argus achieved a maximum value of 0.91, which is already close to the optimum. This means that the robot's performance is high in almost all movement criteria relevant to robotics. These include precise trajectory tracking, robustness, energy efficiency, resistance to damage, and the ability to handle challenging terrain formations. The scientists consider the robot's symmetry to be crucial for its performance.
“When a robot can accelerate equally well in every direction, it stops needing to face the world in any particular way. Forward and backward become the same. Left and right become the same. The whole problem of robot control changes character.”
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The principle of dynamic isotropy developed by the researchers can, in principle, be applied to all robots, making them evaluable according to a uniform system. Robots that are not specifically bound to a particular form can thus be developed in simulations and evaluated based on dynamic isotropy, and subsequently built or discarded.
(olb)
