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A stair-climbing robot thanks to rimless "walking" wheels

While wheeled robots excel at traversing flat terrain over long distances, stairs and steps have long been a limitation - until now. Researchers in Japan have developed a unique rimless wheeled robot that can "walk" up and over raised surfaces using dynamic, telescoping legs in place of conventional rigid wheels.

The innovative bot, introduced in a new paper in Artificial Life and Robotics, represents a promising step toward extending the capabilities and environments where wheeled robots can operate reliably.

"Rimless wheel robots that can walk in environments with steps have not yet been developed," explain authors Yuta Hanazawa, Yuhi Uchino and Shinichi Sagara from Kyushu Institute of Technology. "Our robot with elastic telescopic legs overcomes this challenge, able to nimbly ascend steps using complex walking motions."



From Rolling to Striding 

Most wheeled robots are limited to smooth, level surfaces due to the inherent mechanics of their spinning wheels and risk of catching on obstacles like steps. The researchers aimed to solve this constraint by replacing rigid wheels with elastic, telescoping "legs" that produce a gait-like walking motion rather than a conventional roll.

Through simulations and 3D design iterations, they optimized parameters like leg elasticity and geometry to achieve a stable "step-climbing" ability. Their final physical prototype features three radially-arranged segmented legs that extend and retract, lifting the robot up and over raised surfaces fluidly through a multi-phase "stride" pattern.

"We first used simulations to derive the optimal leg elasticity for overcoming steps reliably," said Hanazawa. "Then constructed a real model adhering to those parameters for real-world testing."


Passing the Step Test 

In a series of experiments, the researchers successfully demonstrated their rimless wheeled robot traversing completely flat ground as well as confidently ascending a 3cm high step - a sizable height relative to the robot's overall size.

Footage shows the trio of telescoping legs compressing as they make contact with the step's edge, storing energy to complete a vaulting "step-up" maneuver. Once lifted onto the raised surface, the legs quickly stabilize for continued striding.

"We confirmed our robot could rapidly overcome the step without getting stuck or falling over," said Hanazawa. "Versus conventional wheeled designs, this rimless 'walking' approach opens up new environments for reliable navigation."

The agile step-climbing ability stems from the robot's unique locomotion dynamics. By removing wheel rims and intelligently controlling the telescoping leg motions, the robot replicates the push-off, flight, and landing phases of legged mobility - albeit with the mechanical simplicity of just spinning leg segments rather than complex joints.


A Step Toward More Mobile Robots 

Looking ahead, the researchers aim to further optimize their robot's control algorithms and energy efficiency while exploring variations like a minimalist one-wheeled version for confined spaces.

Their novel design points toward expanding the mobility and autonomy of wheeled robots used across applications like inspection, monitoring, delivery and emergency response - environments where steps, curbs or rubble could derail conventional wheeled platforms.

"We believe our rimless approach combining wheeled structural simplicity with legged agility can enhance wheeled robots to handle more challenging terrain," said Hanazawa. "Allowing them to go places they previously could not."

As robots continue pushing into more areas of human environments and real-world operating domains, innovations like the walking wheeled robot could be critical to ensuring reliable navigation. With a unique hybrid locomotion that is part wheeled vehicle, part striding mechanism, the rimless robot may open doors to new robotic capabilities - one agile, climbing stride at a time.

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