A TAIL OF TWO DEGREES
A supernumerary robotic tail, based on the kangaroo, may be better disposed to assist balance than other robotic options.
Written by Kayt Sukel
Doctoral student Eisa Anwar helped design, build, and (in this case) demonstrate the robotic tail. Photo: Queen Mary University of London
ACCORDING TO THE CENTER FOR Injury Prevention and Control, falls—particularly in those in adults over the age of 65 years—cost the healthcare system approximately $50 billion annually. To prevent falls in the elderly and those with disabilities, as well as to help those working in manufacturing and other industries, several engineering laboratories have looked at designing robotic systems that offer balance support. Sajeeva Abeywardena, now a lecturer in robotics at the University of Surrey in the United Kingdom, said many researchers have tried their luck with exoskeleton-type systems, but they often come with significant downsides.
“The problem with these ‘Iron Man’ type exoskeletons is that the motors are directly attached to the wearer’s joints,” he explained. “That means there’s no real one-size-fits-all solution. You need to do a lot of tailoring for each individual person.”
However, the addition of a supernumerary robotic tail could eliminate the need for such specific customization. Abeywardena said they can offer a balance assist using “the principles of motion” at the back instead of trying to augment direct torque at a joint.
“A tail can apply force to your body which will then be distributed throughout your limbs, as opposed to trying to directly augment your joints,” he explained.
Abeywardena, together with Eisa Anwar, Stuart Charles Miller, and Ildar Farkhatdinov, wrote about what could be done with such an appendage in the paper, “Mechanical Characterization of Supernumerary Robotic Tails for Human Balance Augmentation,” published in the June 2024 issue of the ASME Journal of Mechanisms and Robotics.
While working as a post-doctoral fellow at the Queen Mary University of London in Farkhatdinov’s laboratory, Abeywardena and colleagues investigated the feasibility of a system designed to mimic a kangaroo’s tail. Their tails, which move up and down, provide significant support as they hop, especially at speed.
“The way we tackled it was to look at this idea theoretically, taking a first principles approach,” Abeywardena said. “Others have worked on tails before and have found they are bulky and don’t provide as much of an assist as hoped.”
A robotic tail, combined with augmentive arms and other exoskeletal components, could help people carry out cumbersome tasks with ease. Image: Lyalya Bulanova, Queen Mary University of London
“The basic way that a kangaroo tail works is that it uses inertia to create an augmentation to support balance.”
– Sajeeva Abeywardena, robotics lecturer, University of Surrey, United Kingdom
Many of the challenges in designing an effective supernumerary tail come down to the design of the structure itself—where to house components and motors in ways that don’t make the tail too long or heavy. When searching for a way to best incorporate robotic components so that elderly wearers can also easily bear the weight, the group determined the best approach would be a tail that offers two degrees of freedom.
“The basic way that a kangaroo tail works is that it uses inertia to create an augmentation to support balance,” Abeywardena said. “And we determined that you don’t need a tail to look like an animal tail to help human balance. Instead, you can exploit the principles of mechanism theory to inform your design, which may be more beneficial to the human body.”
Ildar Farkhatdinov (left), Sajeeva Abeywardena (center), and Eisa Anwar (right) studied the ability of a simple robotic tail to improve balance in humans. Photo: Queen Mary University of London
Using simulation, the researchers determined a closed loop system with two degrees of freedom could help minimize the mass of a supernumerary robotic tail system, while also providing greater force.
“It really came down to looking at the inertia metrics using a first principles approach,” he said. “We had closed linkages that interplay with one another to help motion move from one joint to the other.”
As researchers look to create unique robotic tail designs for different applications, Abeywardena said they can use those vital first principles to help them manage trade-offs between size and workspace. “For example, if someone is working in a warehouse, they can maybe support a little bit more mass on their back,” he explained. “In a rehabilitation center, where you now see people using exoskeletons or robot walker trainers to help people regain function, you might need a more lightweight robot where you can tailor the motion and assistance from the tail based on how the user is recovering.”
Kayt Sukel is a technology writer and author in Houston.
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