A Monocycle Robot with Two Legs

Newswise — Wheels and legs each have their advantages, so why not combine both? ECE associate professor Joohyung Kim has created “Ringbot,” a monocycle robot with two legs. The hybrid leg-wheel mechanism enables the robot to tackle diverse terrains, from urban areas to indoor environments. The robot’s ability to maneuver through narrow spaces means this design can be adapted for last-mile deliveries in congested environments.

This is not the first robot to use a wheel-leg design, but Ringbot might be the first wheel-leg design inspired by monocycles. Kim explains, “The inherent advantages and disadvantages of wheeled and legged robots have motivated robotics researchers to delve into wheel-leg transformable robot design to integrate the strengths of both types.” 

Unlike the unicycle, where the rider sits above the wheel, the rider of the monocycle sits inside the wheel. For human riders, monocycles pose many challenges: the wheel is usually directly in the center of vision, and they can be tricky to turn and control at lower speeds. The Ringbot design avoids some of these pitfalls. The large wheel doubles as the body frame of the robot itself, while the integrated legs help the monocycle to balance and prevent falls. 

Kim’s team observed how humans use their legs when operating compact wheeled vehicles and applied this to their technology. Each of Ringbot’s two legs is mounted on a driving module inside the wheel, and the driving modules are comparable to “two hamsters in a hamster wheel.”

It may look strange and futuristic, but the monocycle robot has a very practical application: last-mile deliveries. “In big cities, many bikes and motorcycles navigate through traffic to fulfill delivery needs, thanks to their ability to maneuver through narrow spaces,” Kim comments. “We plan to enhance Ringbot's capabilities specifically for last-mile deliveries in congested settings, aiming to automate and optimize delivery processes.” Hyundai Motor Group has provided the initial funding to seed this idea.

Ringbot’s unusual design was inspired by science fiction vehicles such as the vehicle General Grievous uses in Star Wars. Kim hopes that the success of Ringbot can inspire fellow researchers and fans of scientific stories to explore their own dream projects. “In essence, I believe the ‘Anything is possible’ moment from the movie ‘Tomorrowland’,” he says.

In the next stages of research, Kim’s team wants to enable Ringbot to carry out last-mile deliveries autonomously. They plan to add two additional limbs so the robot can hold packages within the wheel while using its legs to move along the ground. Kim says, “With this enhancement, Ringbot will have the capability to swiftly navigate roads using its wheels while traversing stairs and rough terrains using its legs.” The best of both worlds. 

Associate professor Joohyung Kim is also a member of the Coordinated Science Laboratory in The Grainger College of Engineering. You can read the full paper online in IEEE Transactions on Robotics: K. G. Gim and J. Kim, "Ringbot: Monocycle Robot With Legs."