Multi-segmented Adaptive Feet for Versatile Legged Locomotion in Natural Terrain

Most legged robots are built with leg structures from serially mounted links and actuators and are controlled through complex controllers and sensor feedback. In comparison, animals developed multi-segment legs, mechanical coupling between joints, and multi-segmented feet. They run agile over all terrains, arguably with simpler locomotion control. Here we focus on developing foot mechanisms that resist slipping and sinking also in natural terrain. We present first results of multi-segment feet mounted to a bird-inspired robot leg with multi-joint mechanical tendon coupling. Our one- and two-segment, mechanically adaptive feet show increased viable horizontal forces on multiple soft and hard substrates before starting to slip. We also observe that segmented feet reduce sinking on soft substrates compared to ball-feet and cylinder-feet. We report how multi-segmented feet provide a large range of viable centre of pressure points well suited for bipedal robots, but also for quadruped robots on slopes and natural terrain. Our results also offer a functional understanding of segmented feet in animals like ratite birds.

I. Introduction

We envision that robust and reliable legged robots will support us not only at home and in our indoor work spaces. Ideally, they will work wherever humans go and beyond. Fields, forests, and mountains are examples of natural en-vironments to which vehicles have limited access. Where animals roam naturally, most wheeled and tracked vehicles are hindered by terrain roughness, slopes, available space, and natural substrates. Towards the goal of legged robots in natural environments, here we aim to design and characterize multi-segmented robot feet mounted to a bird-inspired robot leg. With animals as models in mind, we want to equip our robots with feet that mechanically adapt their shape to comply with rigid, uneven terrain and grab into soft terrain. Bipedal robots require feet with a range of viable center of pressure (CoP) points, or they must constantly and actively be balanced [1]. This criterion disqualifies com-monly mounted ball- and cylinder-shaped feet that otherwise perform well on quadruped legged robots [2], [3].