Wheels are essential for cars, trucks, bikes, and wheelchairs, yet their limitations on uneven surfaces often confine wheelchair users to smooth, flat terrain. The same challenge applies to mobile robots. Recognizing this, a team of Korean researchers has developed a groundbreaking adaptive wheel that changes shape in real-time, allowing for smoother travel over obstacles and rough terrains, revolutionizing off-road mobility.
Reimagining the Wheel
While the idea of “reinventing the wheel” might seem like an exaggeration, this innovation builds on a history of transformative wheel designs. Years ago, Hankook, in collaboration with Seoul National University and Harvard, created origami-inspired wheels that could change shape. Earlier still, graduate student Ackeem Ngwenya developed the “Roadless” wheel system, where the tread adjusted from narrow to wide with a simple screw turn. Even NASA contributed with its nickel-titanium alloy tires, which could deform under pressure and return to their original shape.
Traditionally, track-based locomotion systems have been employed to overcome uneven terrain by increasing the wheel’s surface area. However, these systems are limited to low speeds and require more energy due to the high friction between the tracks and the ground.
Innovative Design for Harsh Terrains
The new adaptive wheel uses airless, non-pneumatic tires, which are resistant to punctures, leaks, and blowouts, making them ideal for rough terrains. However, the stiffness of these tires poses a challenge in overcoming high obstacles. To address this, the researchers drew inspiration from the surface tension of liquid droplets. This phenomenon, caused by an imbalance in cohesive forces between molecules, leads a liquid droplet to maintain a circular shape.
The key to the adaptive wheel’s success lies in its “smart chain structure.” This structure consists of a chain of blocks around the wheel’s exterior, connected by wire spokes to opposite sides of a central hub. By adjusting the gap between the two sides of the hub, the length of the spokes can be varied, altering the shape of the outer chain of blocks. When the hub gap is increased, the spokes shorten, pulling the chain blocks inward to create a circular wheel for quick and efficient travel. Conversely, reducing the hub gap lengthens the spokes, loosening the chain blocks and allowing the wheel to deform, enabling it to overcome obstacles.
Testing and Application
The researchers tested the adaptive wheel on both a two-wheeled wheelchair and a four-wheeled vehicle. In these tests, the wheels successfully adapted to and traversed large steps and irregularly shaped rocks up to 1.2 times the height of the wheel’s radius. In one demonstration, a two-wheeled wheelchair, weighing 120 kg (265 lb), easily navigated uneven, grassy terrain. Although the extreme forward tilt of the chair raises concerns about occupant safety, the technology’s potential is clear.
While no video of the four-wheeled vehicle in action has been released, images provided by the researchers suggest similarly impressive performance.
Conclusion: A New Frontier in Mobility
This innovative wheel design represents a significant leap forward in off-road mobility for wheelchairs and other vehicles. By allowing wheels to adapt to varying terrains in real-time, this technology could greatly expand the freedom and accessibility of those who rely on wheelchairs, as well as enhance the versatility of mobile robots and other vehicles in challenging environments.
By Impact Lab