stabilization and maneuvering are achieved by planning proper leg motions .
In the lab , we didn ’ t yet connect the tail to an actual robot , instead feeding sensor data from the tail into a software model of a quadruped whose legs had only two degrees of freedom . ( Basically , the legs moved at the hips and bent at the knee and ankles .) We simulated a case where the robot would jump in the air and swing its tail to reorient its body , as does a cheetah . In another test , the tail rolled from side to side in order to help the robot regain its balance . In both instances , we were able to show that the tail should be able to allow a robot with very simple legs to perform complex maneuvering , though obviously those results need to be validated in physical experiments .
Those experiments were static ; the simulated robot was not walking . We have also conducted some experiments with a simulation of an even more simplified quadruped , one using the Bioinspired One-degree-of-freedom Leg for Trotting ( BOLT ) which we have developed . We have data from a physical model of the leg and used that to simulate a model of a reduced complexity quadruped . Now , we have modeled dynamic motion with a pendulum-style tail rather than an articulated one , but even such a limited tail was able to provide stability as the robot ran with a bounding gait and enable a ( somewhat ) graceful landing when airborne . It ’ s expected that a fully articulated tail would perform even better , since such a tail would be able to control all the three torso motions — the yaw , pitch , and roll motions — which a pendulum tail cannot do .
Advantage in Mobility
This research is promising , but there is still a long way to go to completely decode the advantage of tails on animals — and for robots . However , for the impending future , there are certain foreseeable concrete tasks that we plan to do . The first task is to improve the robotic tail hardware to make it more reliable and efficient . The second is to build the quadruped robot hardware and to develop dynamic locomotion algorithms for the R3RT case .
So far , the choice of the reduced complexity quadruped is mainly based on engineering considerations . Performing a study that involves the incorporation of an articulated robotic tail on a general legged platform ( without reducing leg complexity ) as a complete coupled physical system will , of course , be the ultimate test . Only then will we be able to qualitatively and quantitatively measure the tail ’ s effectiveness in providing a legged robot with effective maneuvering and stabilization functions , since such a setup is closer to the natural observations seen in animals .
If tails do provide an advantage in mobility , then it seems likely that they will help robots walk and run in a way that seems more natural to people . Rather than the machine-like steps of the NYPD ’ s robotic dog , future robots may be able to move in ways that seem less alienating and more inviting .
Pinhas Ben-Tzvi is a professor of mechanical engineering and electrical and computer engineering and the director of the Robotics and Mechatronics Lab at the Virginia Polytechnic Institute and State University in Blacksburg . Yujiong Liu is a doctoral student in mechanical engineering at Virginia Tech . The research reported in this article is supported by the National Science Foundation under Grant Nos . 1334227 , 1557312 , and 1906727 .
Ongoing prototype development of a cheetah robot on which a bio-inspired robotic tail will be integrated .
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