An Untethered Jumping Robot Made of Shape Memory Polymers

Jumping is a crucial ability that enhances the mobility of natural creatures, enabling them to navigate intricate terrains effectively. In nature, achieving jumping often requires complex and specialized shapes that can store and release energy efficiently, which has inspired the development of soft jumping robots as a promising solution for rapid and dynamic locomotion across diverse environments. To replicate these complex shapes, thermally responsive shape memory polymers (SMPs) are particularly promising due to their ability to deform, recover, and be reprogrammed to adopt different shapes in response to external heat. Despite these promising attributes, SMP-based soft robots are still limited, primarily due to the intrinsic slow response speed of SMPs. Additionally, although other jumping mechanisms have been explored, these solutions often require extra energy storage structures or extremely high energy input. To address these challenges, this study investigates a novel mechanism for achieving jumping behavior in soft robots using SMPs without requiring high energy input or extra structures through experiments and finite element analyses. Specifically, the proposed design employs a self-contacting spiral structure to store and rapidly release elastic energy upon moderate heating, thereby enabling efficient jumping. By incorporating liquid metal particles into SMPs, the thermal response speed is significantly enhanced, which, in turn, enables faster actuation. Moreover, a double spiral design inspired by human biomechanics is implemented to further control the jumping direction and to increase the jumping height. SMP spirals are also adapted for projectile launching, mimicking the seed dispersal mechanisms of plants, wherein a small load is thrown upon sudden energy release. These findings provide valuable design guidelines for future jumping soft robots, emphasizing the importance of material choice, efficient energy storage, and control mechanisms to achieve optimal jumping performance.