Legged locomotion is commonly studied and expressed as a discrete set of gait patterns, like walk, trot, gallop, which are usually treated as given and pre-programmed in legged robots for efficient locomotion at different speeds. However, fixing a set of pre-programmed gaits limits the generality of locomotion. Recent animal motor studies show that these conventional gaits are only prevalent in ideal flat terrain conditions while real-world locomotion is unstructured and more like bouts of intermittent steps. What principles could lead to both structured and unstructured patterns across mammals and how to synthesize them in robots? In this work, we take an analysis-by-synthesis approach and learn to move by minimizing mechanical energy. We demonstrate that learning to minimize energy consumption is sufficient for the emergence of natural locomotion gaits at different speeds in real quadruped robots. The emergent gaits are structured in ideal terrains and look similar to that of horses and sheep. The same approach leads to unstructured gaits in rough terrains which is consistent with the findings in animal motor control. We validate our hypothesis in both simulation and real hardware across natural terrains.
In Biomechanics, Froude number is a metric characterizing gaits of quadrupeds and bipeds. Animals with a similar morphology but with different sizes tend to use the same gait when moving with equal Froude numbers. Our robot has similar Froude numbers as horses and sheep. The plot on the left (Hoyt et al. 1981) analyzes the energy consumption of different horse gaits across different speeds. Shown on the right, the energy consumption plot of our robot has a similar trend, which also validates certain gaits will emerge at certain speeds if we minimize the energy consumption.
Foot Contact Plots of Walking, Trotting, Bouncing (Galloping)
Ashish Kumar, Zipeng Fu, Deepak Pathak, Jitendra Malik RSS 2021 PDF | Video | Project Page |
Zipeng Fu*, Ashish Kumar*, Ananye Agarwal, Haozhi Qi, Jitendra Malik, Deepak Pathak CVPR 2022 PDF | Video | Project Page |
@inproceedings{fu2021minimizing,
author = {Fu, Zipeng and Kumar, Ashish and Malik, Jitendra and Pathak, Deepak},
title = {Minimizing Energy Consumption Leads to the Emergence of Gaits in Legged Robots},
booktitle = {Conference on Robot Learning ({CoRL})},
year = {2021},
}