Wheels that can transform from traditional round shapes into a triangular track could enable vehicles to operate at high speeds on roads and diverse off-road terrains. Developed by researchers at the Carnegie Mellon University (CMU) National Robotics Engineering Center (NREC) as part of a Defense Advanced Research Projects Agency (DARPA) program called Ground X-Vehicle Technologies (GXV-T), the wheels can transform between modes in less than two seconds while the vehicle is in motion.

“This shape-changing locomotion technology could enable vehicles to tackle a wide array of terrains at surprising speed,” says Dimi Apostolopoulos, a CMU Robotics Institute senior systems scientist who led the project at NREC. “Based on the testing we've done so far, we would expect such a vehicle to do amazing things.”

DARPA's GVX-T program aims to reduce the need for armor by making combat vehicles faster, more maneuverable, and capable of operating in various environments. Apostolopoulos says the shape-shifting wheel-track has potential civilian applications, including uses in forestry, mining and construction, and heavy equipment.

In testing, vehicles equipped with the reconfigurable wheel-track have reached 50mph in wheel mode and almost 30mph in track mode. The device has transformed from wheel mode to track mode at speeds as high as 25mph and from track mode to wheel mode at speeds around 12mph.

The core of the wheel-track concept is to adjust the size of the contact patch – the area of the wheel-track in contact with the ground – based on surface type and wheel loading. Reducing the contact patch on smooth surfaces allows higher speeds. Increasing the contact patch maximizes traction, much like a snowshoe, and enables the vehicle to maneuver safely on soft soils. Today's Humvees do something similar by increasing tire pressure on smooth, dry surfaces and reducing tire pressure in off-road situations, Apostolopoulos says.

Other groups have created similar reconfigurable wheel-tracks, but those usually require halting the vehicle to change modes, Apostolopoulos notes.

An experimental military vehicle uses hybrid wheels developed by researchers at Carnegie Melon University that can transform from round for on-road use to tracks for off-road.
Photos courtesy of Carnegie Melon University National Robotics Engineering Center

The reconfigurable wheel-track has a rubberized tread on a frame that can change shape. An early version used electric motors to change the frame’s shape, but the researchers realized they could transform the shape passively, using the speed of the wheel-track to power the shape change.

In its latest manifestation, the spinning wheel is transformed into a track by extending a Y-shaped support, which pushes the frame into a triangular shape. Simultaneously, a brake stops the wheel from spinning, causing the transmission to automatically shift from turning the wheel to turning a set of gears that drives the track.

NREC is a part of Carnegie Mellon's Robotics Institute that performs contract research and development for a variety of governmental and industrial clients.

Carnegie Mellon University National Robotics Engineering Center https://www.nrec.ri.cmu.edu

Defense Advanced Research Projects Agency https://www.darpa.mil