Yale Engineers Design Bio-Inspired Variable-Stiffness Morphing Limb for Amphibious Robots
The morphing amphibious limb design may enable the next generation of hybrid soft-rigid robots to adapt to unstructured environments.
Engineers and roboticists have been designing robots that can swim in oceans and lakes with high efficiency, or traverse on nearly any terrain on land without falling. Some are bio-inspired like Boston Dynamics' Spot, or MIT's soft robotic fish, which mimic the way natural animals move in their environments. Now, researchers from Yale's Faboratory have developed a tortoise/sea turtle morphing limb that would bring about a new kind of amphibious robot by being able to transition between the flipper and leg configurations.
Amphibious robots present a unique challenge in that to transition from the land to sea (or vice versa), they must change or adjust their means of locomotion, which is easier said than done. Most use wheels, rotors, or jets for the transition, which is highly inefficient as land requires a rigid platform for movement, while an aquatic setting benefits from a flexible limb. To get around this issue, the engineers have created a variable-stiffness morphing limb that can transition between stiff and flexible on-demand.
The morphing limb was designed using a variable stiffness composite material, which acts as a sleeve that's coupled to a pneumatic actuator system that enables the transition between flipper and leg. The stiffness is controlled by varying an electrical input to Joule-based flexible heaters bound to the composite material, which softens it, turning it into its flipper state. When the pneumatic actuators inflate the material, it then converts into a rigid limb once cooled, thus morphing it into a leg.
While the morphing limb is promising for amphibious robots, it still needs further development, as the engineers found that when transitioning the limb to a rigid state, the amount of time required was about 15 minutes, so it's not exactly an on-demand transformation while on land or sea. This is due to the fabric and actuators, which act as insulators, and while they cool quickly in water, transitioning using heat takes time to transition on land.