This Tiny 4-Inch Robot Hops, Backflips and Swims Using an Odd Trick Hidden in Its Legs

A new frog-like robot has demonstrated the ability to hop, backflip, and swim using an unusual mechanism involving the snapping of thin metal rods. The robot, measuring 4.3 inches in length, uses two slender metal rods wound around a motor to generate forceful, rapid movements. In testing, it hopped across various surfaces, achieving an average speed of 2.46 body lengths per second, roughly three times faster than a similar robot with rigid legs. The robot's performance was particularly notable on soft surfaces like cloth and grass, where it outperformed its rigid-legged counterpart. The study, published in Science Advances, highlights how the geometry of the rods determines whether they snap or bend gradually, offering a way to optimize robotic movement.

The robot's limbs are equipped with thin rods of Nitinol, a flexible nickel-titanium alloy, held in a helical shape. A motor rotates one end of the rod, causing it to store elastic energy until it reaches a tipping point and snaps into a new shape. This sudden release of energy launches the robot into a hop. The robot can hop up and down steps and follow a teleoperated route through sand, demonstrating its versatility. The study notes that the robot's performance on soft surfaces is attributed to the ability of the snapping limbs to deliver a quick, powerful kick rather than relying on continuous contact with the ground. The robot's design allows for controlled, repeatable snaps, which is crucial for efficient movement.

The study's findings provide a method to predict when an elastic rod will snap, enabling designers to choose the right configuration for their robots. The robot's lightweight design, weighing 98.2 grams, and its ability to perform multiple hopping cycles per second make it a promising candidate for applications in environments where traditional motors struggle. The research also suggests that similar principles could be applied to smaller robots, potentially leading to more efficient and powerful movement. The study emphasizes that the shape of the rod, rather than its size, determines whether it snaps or deforms, offering a versatile approach for a wide range of robotic applications.

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