Tiny knot robots jump, fly and sow seeds

A team of scientists from the University of Pennsylvania has developed a tiny robot that catapults itself into the air by dissolving its knot-like structure and moves forward by flying with a rotor blade. The robot can contain a plant seed, which is sown where the robot lands.

Knotted fibers are commonly considered something passive. However, if the elasticity and material are carefully selected, the knot itself becomes an active system, explains Shu Yang, Professor of Materials Science and Engineering at the University of Pennsylvania. The research team used this to construct a robot consisting of a fiber less than a millimeter thick made of Kevlar and a liquid crystal elastomer (LCE), as described in the study “Programming touch-me-not knot topologies for rapid and diverse leaping and flying motions,” published in Science.

“Programmable” Jumping System

The two different materials of the robot perform different tasks: the Kevlar core provides the necessary stiffness, and the surrounding elastomer provides flexibility. The resulting composite fiber, a few millimeters long, is then knotted. This stores elastic energy in the system. Depending on the material combination used, the knot can open itself sooner or later when heated between 60 and 90 °C – for example, by solar heat. This is because the LCE sheath contracts under heat, causing the knot to loosen and open.

The kinetic energy is then released in fractions of a second and converted into a jumping motion that catapults the robot about two meters high into the air. The researchers can “program” the reaction time and the strength of the jump by adjusting the material combination, the knot topology, and the pre-twisting of the fiber. The type of knot determines the flight motion performed. A simple overhand knot leads to a tipping motion, while a figure-eight knot leads to a rotation. More complex knot shapes can generate further movement patterns.

The scientists have equipped the small robot with a leaf-like structure, which, similar to a maple seed, ensures that the flight is more stable and it can stay in the air longer and fly further. Upon landing, the fiber embeds itself almost vertically into the ground, generating such high pressure that a carried seed can be sown promisingly.

At its current stage, the robot is a model system designed to demonstrate the fundamental feasibility. Practical versions would need to consist of environmentally friendly components so that the robot biodegrades. The scientists are also investigating how to lower the activation temperature to enable the robot to be used in regions with less solar radiation.

(olb)