Letting 'Short-Stature' Robots Jump High and Go Far (Innovation Roundup)

　　Moving, jumping, flipping, landing, jumping again... Under constant infrared illumination, a millimeter-scale soft robot is autonomously completing continuous jumps. Recently, a research team from North Carolina State University in the United States published results in the Proceedings of the National Academy of Sciences, proposing a new type of self-resetting soft ring-jumping robot. This tear-drop-shaped 'little guy' robot athlete does not require manual resetting or complex control systems; it can perform over 1,000 consecutive jumps under constant illumination solely relying on the 'physical intelligence' of its material and structure. The maximum vertical jump height reaches 80 times its own height, and the horizontal jump distance exceeds three times its own length. 'The key of this work is not to achieve continuous jumping through complex mechanical mechanisms or electronic controls, but rather by combining liquid crystal elastomer smart materials with a ring structure, to 'write' the entire motion cycle of energy storage, release, jumping, and resetting into the robot itself,' said Yin Jie, the corresponding author of the study and professor in the Department of Mechanical and Aerospace Engineering at North Carolina State University, in an interview with this newspaper.

　　Continuous jumping is an effective mode of movement for navigating complex, unstructured environments. However, achieving autonomous continuous jumping for soft robots is not easy: it requires energy storage and release that can be repeated, automatic reset after landing, maintaining a stable posture in the air, and adapting to different terrains. Many soft jumping robots in the past could only perform a single jump; to achieve continuous jumping, they often required manual reset or continuous external stimulation. Due to their complex structures, they are also prone to disturbances during takeoff and landing, making it difficult to stably recover a posture suitable for the next jump.

　　In response to this, the research team started with structural design and proposed a simple solution. The soft ring is made of liquid crystal elastomer material, which is bent into a ring shape, with the two ends connected by aluminum tubes to form a closed-loop structure with a V-shaped rigid tail. Liquid crystal elastomers are smart materials that can convert optical or thermal stimuli into shape changes. Under constant infrared illumination, the material contracts due to heating; since there is a temperature difference between the illuminated side and the shaded side, the soft ring spontaneously twists, storing elastic energy like winding a spring.

　　As the torsion continues to accumulate, the V-shaped rigid tail gradually bends and lifts. Once the critical state is reached, the structure suddenly becomes unstable, and the stored elastic energy is rapidly released, causing the tail to strike the ground at high speed and launch the soft ring into the air. After leaving the ground, the twisted soft ring automatically untwists and returns to its original shape in the air. Upon landing, it can once again store energy and jump again. The entire process does not require onboard sensors, electronic controllers, or repeated manual intervention.

　　“The ring structure solves the problem of whether the robot can perform continuous jumps, while the center of mass adjustment helps address whether it can maintain stable direction during jumps toward the target.” said Yin Jie. The so-called center of mass adjustment refers to adding a small amount of counterweight at the front of the ring body, shifting the robot's mass distribution forward, thereby suppressing large-scale flipping and improving the directional stability of continuous jumps. By adjusting the tail angle, counterweight ratio, and light intensity, the robot can switch between crawling, directional jumping, and vertical jumping.

　　Chen Tao, a researcher at the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, and the National Key Laboratory of Marine Key Materials, told reporters that in the past, each jump of a soft robot required manual reset or external modulation. This was because, under constant external stimulation, achieving a cyclic 'energy storage—energy release—reset' closed loop was extremely difficult, requiring simultaneous energy recovery, aerial attitude stabilization, and energy replenishment upon landing. This work replaces bending and stretching energy storage with torsional energy storage, and encodes the reset process into the structure itself through geometric constraints, providing a highly simplified path for continuous jumping of soft robots.

　　This structure is not limited to terrestrial jumping. The research team further modified the materials and tail design to enable the soft ring to float, swim, and return to the shore, achieving an amphibious motion of 'jumping—swimming—jumping again'. On the water surface, the tail switches from 'ground-pounding takeoff' to 'water-paddling propulsion'; when reaching an inclined shore, the thrust generated by the tail's bounce can also help it overcome surface tension to return to land.

　　In terms of application prospects, Yin Jie believes that such millimeter-scale soft robots, due to their small size, light weight, and flexible structure, are suitable for entering complex environments such as grassland, gravel, mud, shallow water, and water-land boundaries. In the future, if multi-robot collaboration is achieved, they may also be extended to cluster-based environment exploration and large-scale distributed monitoring.

　　Moving from the laboratory to practical application still has a long way to go. The next step, the research team hopes to explore the use of natural light, enabling the robots to be independent of fixed artificial light sources. Yin Jie stated that the significance of this work does not lie in creating a mature outdoor robot product, but in proving that a very simple millimeter-scale soft robot can rely on the physical intelligence of its material and structure to achieve continuous, adaptive autonomous movement, providing new design ideas for future micro-robots to enter real non-structured environments.