This Manta Ray-Inspired Robot Can Swim, Like, Really Fast

Almost all early attempts at human-powered flight and flying machines mimicked nature and resembled bird or bat wings. Leonardo Da Vinci envisioned something more like modern helicopters and it took centuries for his ideas to catch on. In the same vein, bio-inspired robots tend not to perform as well as those that rely on conventional mechanical joints. Biological tissue is complex and difficult to reproduce with artificial materials. When those materials don’t match the properties of biological tissue, the whole concept falls apart. To create a fast-swimming soft robot,North Carolina State University engineers put effort into mimicking the body movement of a manta ray.

Soft robots in general tend to better reproduce the characteristics of biological tissue, but that isn’t saying much. Silicone is obviously more tissue-like than steel. That doesn’t mean that it actually acts like skin or muscle. Instead of trying to produce a perfect recreation of biological tissue, these engineers focused on accurately matching the movement of a manta ray’s body as it swims. The key to that breakthrough turned out to be bistable “wings” that provide strong propulsion through water, resulting in a soft robot that can swim faster than previous designs.

A bistable mechanism is one that remains in whichever of two states an outside force sets it to. A household light switch, for example, is a bistable mechanism. It will remain in either the on or off position once set, without requiring power to retain its state. In a similar way, this robot’s wings want to move into either the upward or downward position and then stay there. It takes a small amount of force to change states, but the intermediate positions are unstable and the wings naturally want to finish the movement to snap into a stable position. An inflatable chamber in the robot’s body acts like a muscle to provide the force necessary to change between stable positions.

However, that arrangement doesn’t allow for maneuvering and the described robot can only swim forward. To change direction, the team had to build a slower robot with each wing controlled independently by its on bladder muscle. That can turn as it swims, but it is less efficient and can’t swim as fast as the simpler robot. The speedy robot can swim at 3.74 body lengths per second, while the maneuverable robot can only maintain 1.7 body lengths per second. The latter is still fast compared to similar robots, but the former is possibly the fastest robot of this type.