Making every step an experiment: proprioceptive sensing during locomotion for enhanced mobility and data collection in earth and planetary explorations*

For legged robots moving through complex, deformable terrains, substrate reaction forces "felt" through locomotive appendages can be more informative than visual or other exteroceptive inputs for inferring environment properties and adapting locomotion strategies. Recent advancements in direct-drive actuators have enabled the development of individual robotic legs with the ability to measure contact forces and terrain characteristics through actuator phase current. The goal of our study is to extend this novel capability from stationarily mounted individual legs to dynamic quadrupedal robots, and develop platforms that can rapidly assess substrate strength and rheology during continuous locomotion. Here we report our results on two aspects of this development: (i) Implementing momentum-based observers to improve the accuracy of force sensing during dynamic motion, and (ii) understanding how different robot locomotive behaviors (e.g., leg touchdown speed and direction, body pose) could inform distinct terrain characteristics. Going forward, these understandings could enable legged robots to select custom locomotive behaviors to effectively gather environment information during every step, and use the information in turn to enhance their mobility during earth and planetary explorations.