Scientists regularly draw ideas from the natural world in a bid to improve robotic performance, and when it comes to soft robots that swim, motion in the ocean is a rich source of inspiration. The latest creation to emerge in this space is a soft robot modeled on the manta ray that mimics the butterfly stroke in humans to move through the water with unparalleled speed.
They developed two types of butterfly bots: one that can reach a speed of 3.74 body lengths per second, which is 4.8 times faster than the reported fastest flapping soft swimmer, and the other with sideways maneuverability, one that can take sharp turns to the left or right with a high turning speed of 157 °/sec and move at a speed of 1.7 body lengths per second.
The soft robotic swimmer can achieve a higher Strouhal number between 0.2 and 0.4 for efficient propulsion, which is used to assess the energy efficiency of flying and swimming animals relating to forward speed, amplitude, and flapping frequency, while its value varies between 0.25 and 0.35 for flapping foils. The swimming bots weigh only 2.8 g.
The two variations are achieved with a different number of drive units attached to the wings. While the faster robot is attached to one drive unit to give it a better speed with restricted sideways movement, the maneuverable bot is equipped with two drive units so that only one of its wings can be activated for it to take a sideways turn.
Although the prototype provides a promising proof of concept, it is not without limitations. For butterfly bots, the central body is tethered with pumping tubes, adding significant weight to the body. He said they are working to improvise it into an untethered and autonomous one.
