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Recently, a research and development team at North Carolina State University developed an energy-efficient softwarerobot, named “Butterfly robot“, as the name suggests, the swimming action of this robot is very similar to butterfly stroke, and its speed is extremely fast. It is reported that its swimming speed is more than four times faster than that of swimming soft Robots that appeared before. The research is based on the paper “Snapping for high-speed and high-efficient, butterfly swimming-like soft flapping-wing robot” was recently published in the journal Science Advances.

The R&D team developed two different types of butterfly robots. One built for speed, capable of reaching an average speed of 3.74 body lengths per second. The other is designed to be highly maneuverable, capable of sharp turns to the right or left. Speeds can reach speeds of 1.7 body lengths per second.

In the animal kingdom, butterflies are powered by their “wings,” which are “bistable,” meaning they have two stable states. The trajectory of the flapping of the wings resembles the figure eight, which is very similar to the trajectory of the wings of hummingbirds and wasps.

If a robot wants to realize such a complex trajectory, it often needs many complex connection structures to form a transmission system. The robot bends its body up and down through driving, which drives the snapping of the two wings to swing up and down and rotate quickly. The inflation and deflation of the driver makes the wings switch back and forth between the upward and downward bending states.

The entire switching process is realized through a sudden jump, which can quickly release the accumulated energy, making the soft robot instantly increase its swimming speed. At the same time, the energy input to the entire system is reduced, thus making the soft robot both fast and efficient. As it swims, the entire body of the soft robot will undulate, much like the undulations from head to torso when humans swim butterfly. The difference is that this soft robot can obtain huge thrust no matter whether it flaps its wings downward or upward.

This soft robot has unique locomotion advantages and disadvantages, but it can only swim forward in one direction. To address this limitation, the R&D team further developed the faster Butterfly robot—a maneuverable flapping-wing swimming robot capable of directional steering.

The robot consists of a multi-stable soft flapping actuator, two soft pneumatic bending actuators connected in parallel in the middle as a soft body, and two bistable wings with wrapped membranes and extended flexible fins that can both operate under a single drive. Flap independently for cornering motions or simultaneously with dual drive for forward motions for increased maneuverability.

“Most previous attempts to develop flapping-wing robots have focused on using electric motors to directly power the wings,” said the team’s researchers. “Our approach uses a bistable wing that is passively actuated by moving a central body. This is an important distinction because it allows for a simplified design and thus reduced weight.”