From mountain goats that run up near-vertical rock faces to armadillos that roll into a protective ball, animals have evolved to adapt effortlessly to changes in their environment. In contrast, when an autonomous robot is programmed to reach a goal, each variation in its pre-determined path presents a significant physical and computational challenge.
Researchers led by Josie Hughes in the CREATE Lab in EPFL’s School of Engineering wanted to develop a robot that could traverse diverse environments as adeptly as animals by changing form on the fly. With GOAT (Good Over All Terrains) they have achieved just that — and created a new paradigm for robotic locomotion and control in the process.
Thanks to its flexible yet durable design, GOAT can spontaneously morph between a flat ‘rover’ shape and a sphere as it moves. This allows it to switch between driving, rolling, and even swimming, all while consuming less energy than a robot with limbs or appendages.
“While most robots compute the shortest path from A to B, GOAT considers the travel modality as well as the path to be taken,” Hughes explains. “For example, instead of going around an obstacle like a stream, GOAT can swim straight through. If its path is hilly, it can passively roll downhill as a sphere to save both time and energy, and then actively drive as a rover when rolling is no longer beneficial.”
To design their robot, the CREATE team took inspiration from across the animal kingdom, including spiders, kangaroos, cockroaches, and octopuses. The team’s bioinspired approach led to a design that is highly compliant, meaning it adapts in response to interaction with its environment, rather than remaining rigid. This compliance means that GOAT can actively alter its shape to change its passive properties, which range from more flexible in its ‘rover’ configuration, to more robust as a sphere.
Built from inexpensive materials, the robot’s simple frame is made of two intersecting elastic fiberglass rods, with four motorized rimless wheels. Two winch-driven cables change the frame’s configuration, ultimately shortening like tendons to draw it tightly into a ball. The battery, onboard computer, and sensors are contained in a payload weighing up to 2 kg that is suspended in the center of the frame, where it is well protected in sphere mode — much as a hedgehog protects its underbelly.
CREATE Lab PhD student Max Polzin explained that compliance also allows GOAT to navigate with minimal sensing equipment. With only a satellite navigation system and a device for measuring the robot’s own orientation (inertial measurement unit), GOAT carries no cameras onboard: it simply does not need to know exactly what lies in its path.
“Most robots that navigate extreme terrain have lots of sensors to determine the state of each motor, but thanks to its ability to leverage its own compliance, GOAT doesn’t need complex sensing. It can leverage the environment, even with very limited knowledge of it, to find the best path: the path of least resistance,” Polzin said.
Future research avenues include improved algorithms to help exploit the unique capabilities of morphing, compliant robots, as well as scaling GOAT’s design up and down to accommodate different payloads. Looking ahead, the researchers see many potential applications for their device, from environmental monitoring to disaster response, and even extraterrestrial exploration.
“Robots like GOAT could be deployed quickly into uncharted terrain with minimal perception and planning systems, allowing them to turn environmental challenges into computational assets,” Hughes says. “By harnessing a combination of active reconfiguration and passive adaptation, the next generation of compliant robots might even surpass nature’s versatility.”
Transcript
00:00:07 navigating complex natural terrain remains Nature's Domain animals effortlessly adapt across diverse Landscapes displaying agility and resilience what if robots could match or even surpass this adaptability we present the goat robot a shape-shifting multimodal robot designed for challenging outdoor
00:00:37 environments its core structure integrates a compliant fiberglass frame two wind driven cables supporting a central payload and four compliant rimless Wheels by adjusting cable length coat changes its shape when lengthening one cable and shortening the other in plain Recon configuration occurs inspired by Nature's reconfigurability like hedgehogs curling up or tumble
00:01:09 weeds rolling with the wind goat can transition from a flat form into a compact protective sphere when unfolding the goat's symmetric design enables it to always assume a feasible driving configuration built from off-the-shelf materials and scalable fabrication methods the goat is lightweight and durable perfect for tough field
00:01:36 [Music] deployments unlike traditional robots that rely on intricate sensing and environmental models the goat Embraces a bioinspired approach actively altering its shape allows it to change its passive properties and to adapt to the environment tested over 4 and 1/2 km of diverse terrains goat proves its
00:02:03 versatility in Snowy Mountains Urban zones and even in water here the robot climbs through a field of large Boulders relying on its compliant structure to maintain traction and stability the robot's rimless Wheels allow it to overcome obstacles half its own height in its fical shape the goat tucks its Wheels inwards protecting them and
00:02:34 its vital payload from the harsh surrounding environment it can safely roll down slopes and cliffs autonomous navigation strategies can leverage the environment itself turning rugged Landscapes into natural guides reducing the need for computation and extensive path planning by reconfiguring the robot can free
00:03:11 itself when stuck the goat's design enhances endurance Energy Efficiency and adaptability integrating active and passive reconfiguration to navigate in extreme and diverse terrains make the goat ideal for applications in environmental monitoring Disaster Response and even extraterrestrial exploration
