Improving the Traction of a Legged Rover: A Biomimetic Approach

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Hexapod robots are becoming increasingly popular for navigating and exploring irregular and inhospitable environments. The Lunar Zebro is such a hexapod robot that has been developed to be the lightest and smallest rover to explore the moon. The purpose of the Lunar Zebro is to navigate the surface of the moon where it will encounter difficult terrains such as regolith (Lunar Soil) and rocks. To date, not much focus has been placed on the design of the Lunar Zebro legs to increase the rover’s trafficability on these terrains. Furthermore, the designs of rover wheels are constantly changing, and new lessons are being learnt from each new mission that the guidelines for designing the wheels and legs of rovers are constantly evolving. Using a Biomimicry design framework, the legs of the Lunar Zebro were redesigned using strategies adopted by animals in nature to improve the trafficability of the legs on granular and rocky terrains. Several concepts were created and narrowed down to four final designs (Hair, Web, Paddle and Claw Legs) that were further developed and manufactured. In addition to this, the original leg design and a flat leg with no grousers were developed for testing.

Several different single-leg tests were performed on the legs to measure their sinkage, thrust, rolling resistance and drawbar pull on regolith and rocky surfaces. The results showed that hair has the potential to reduce sinkage on regolith. However, the results from the single-leg tests on regolith also indicated that there is not much difference in the drawbar pull performance of the different legs no matter what features were included on the bottom of the leg or if the leg had grousers or not. In contrast, the results of the experiments performed on rocky surfaces showed that legs with claw-like grousers performed the best.

From there a hybrid leg was designed using the finding of the single-leg tests and this leg was tested on a basic Lunar Zebro prototype against the original Lunar Zebro leg design to determine if the hybrid improves the trafficability of the rover on both regolith and rocky terrains. These tests included testing the drawbar pull of the rover at 100 % slip and measuring the distance travelled by the rover over five steps. The results showed that on regolith terrain, the design of the leg does not have a big impact on the performance of the rover. However, the results showed that on rocky terrain the rover with hybrid legs travelled roughly 10 % further over five steps and had a drawbar pull roughly 10 % larger than the rover with original legs.