When the Going Gets Tough, Hit the GASS

Getting around in difficult environments, like underwater or on wet surfaces, presents significant challenges for robots due to the complex and often unpredictable conditions they encounter. In these scenarios, traditional wheeled, tracked, or legged robots struggle to maintain stability and traction, making it difficult for them to move efficiently and effectively. Water, for instance, presents obstacles due to its tendency to cause resistance, while wet surfaces exacerbate issues with slippage and reduced friction.

While the best engineers struggle with these problems, nature offers fascinating examples of organisms that can thrive in such harsh conditions. The gecko, for instance, has remarkable climbing abilities, even on slippery surfaces, thanks to the specialized structure of its feet. The gecko's feet feature millions of tiny hair-like structures called setae that interact with surfaces on a molecular level, creating a strong Van der Waals force between the feet and the surface. This natural adhesive mechanism allows geckos to strongly cling to just about any surface, even vertical surfaces.

Similarly, sea stars are well adapted to underwater life with their unique locomotion system. They possess multiple tube feet, which extend and contract through a water vascular system to give them a unique, flexible gait. This system allows sea stars to navigate through aquatic environments and squeeze into tight spaces. Their natural capabilities allow them to overcome challenges like strong currents and buoyancy.

Researchers at Carnegie Mellon University have an interest in replicating these types of capabilities in a soft robot to support operations like deep-sea exploration, pipeline inspection, maintenance and extraction of mineral resources, and biological sample gathering. By leveraging these skills they also see opportunities in healthcare to detect pathogens and adhere wearable patches to collect physiological data. As a step towards enabling these types of use cases, they have developed what they call a Gecko Adhesion Based Sea Star (GASS) Crawler robot that can both swim and crawl on wet surfaces. As the name implies, elements of the robot were inspired by the gecko and the sea star.

GASS is composed of a soft and stretchable elastomer that has five arms that are pneumatically actuated. Individual control of the flexible arms gives the robot excellent amphibious crawling capabilities much like a sea star. At the tip of each limb is a pneumatically actuated expandable gecko patch. The team developed a novel fabrication method that allowed them to pattern microscale structures over the entire patch using diffraction grating arrays that are inexpensive and widely available commercially. When the gecko patches are actuated, they expand and the internal air pressure exerts enough force to attach it to even challenging surfaces.

The combination of adhesion and flexible crawling give the GASS robot a unique ability to navigate wet or dry surfaces with ease, in or out of water. The team tested the robot’s performance on glass, acrylic, and stainless-steel surfaces and it was discovered that it could crawl up 25 degree inclines and statically hold its position on slopes of up to 51 degrees. The addition of the gecko patches were demonstrated to improve the robot’s crawling by a factor of 59 on flat, dry surfaces.

At present the GASS crawler utilizes an open-loop control system, so the team is exploring ways to integrate sensory feedback into the algorithm. They are also looking for ways to simplify the fabrication process to make it more practical for others to build new GASS crawlers. Moreover, the researchers are considering different types of gecko-inspired adhesives that could be used in future versions of the robot — they believe that upgrades could allow the robot to crawl faster, and under more challenging environmental conditions.