Computational Design of Terrestrial Robots with Anisotropic Friction

Anisotropic friction is a critical source of propulsion for efficient locomotion of many terrestrial animals. The interplay between animal morphology, control, and anisotropically frictional contact makes designing optimal anisotropic friction for terrestrial locomotion intriguing and challenging. We propose a computational pipeline for co-designing anisotropic friction and controllers of terrestrial robots with diverse morphologies. Our pipeline presents a co-design algorithm that alternates between optimizing direction of anisotropic friction and training a neural network controller to improve the locomotion performance of a given robot morphology. Based on the intuition that controller’s performance does not change significantly when the frictional force differs slightly, we introduce the concept of trust-region into robot co-design, allowing the controller network to continue training from the previous iteration. Our evaluation on various morphologies show that anisotropic friction is critical for terrestrial robot locomotion, and our pipeline is statistically better than current state-of-the-art methods. Furthermore, we reveal that large language models (LLM) constitute a strong baseline for this kind of co-design problems, worth receiving more attention. We demonstrate that co-designing anisotropic friction and control unlocks effective locomotion in various downstream tasks, including locomotion on uneven terrain, navigation in a maze, and object manipulation. To validate our pipeline in the real world, we design and 3D print a variety of scales and systematically measure their anisotropic friction coefficients. Then we construct a multi-link robot with anisotropic scales designed by our pipeline and compare its performance with isotropic scales. Our real-world experiments confirm that isotropic scales are insufficient to support terrestrial robots’ locomotion abilities, and computationally co-designing friction and control enables robots to perform tasks including turning, slithering, and other non-trivial locomotion tasks.