Flipper-Style Locomotion Through Strong Expanding Modular Robots

Volume-changing robotic units present an exciting pathway for modular robotics. However, current attempts have been relatively limited, requiring tethers, complex fabrication or slow cycle times. In this letter, we present AuxBots: an auxetic-based approach to create high force, fast cycle time self-contained modules. By driving the auxetic shell's expansion with a motor and leadscrew, these robots are capable of expanding their volume by 274% in 0.8 seconds with a maximum strength to weight ratio of 76x. These force and expansion properties enable us to use these modules in conjunction with flexible wire constraints to get shape changing behavior and independent locomotion. We demonstrate the power of this modular system by using a limited number of AuxBots to mimic the flipper-style locomotion of mudskippers and sea turtles. These structures are entirely untethered and can still move forward even as some AuxBots stall and enter a fault state, achieving the key modular robotics goals of versatility and robustness.