An Energetic Analysis of Rhomboidal Linkage Robots for Hopping Lunar Exploration

In this paper, we present a conceptional design framework for jumping robots for lunar exploration. A method is developed for spring placement and sizing that maximises the onboard elastic potential energy storage, which is essential for space missions. In the class of rhomboidal linkage robots, the analysis shows that torsion springs placed at the knee joints store more energy than the commonly used extension or linear compression springs for a given charging-actuator force; torsion springs store around 80% of the idealized maximum attainable elastic energy storage, compared to only 60% for an extension spring. A physical demonstrator is developed using torsion springs, and exhibits repeatable jumps with an average jump height of 1.1m under earth gravity, equivalent to 6.7m under lunar gravity. However, preliminary trials show the choice of substrate is shown to influence the jump height. This effect is predicted to be pronounced when jumping from lunar regolith.