Highly Dynamic Bistable Soft Actuator for Reconfigurable Multimodal Soft Robots

Matching the rich multimodality of natural organisms, i.e., the ability to transition between crawling and swimming, walking and jumping, etc., represents a grand challenge in the fields of soft and bio-inspired robotics. Here, a multimodal soft robot locomotion using highly compact and dynamic bistable soft actuators is achieved. These actuators are composed of a prestretched membrane sandwiched between two 3D printed frames with embedded shape memory alloy (SMA) coils. The actuator can swiftly transform between two oppositely curved states and generate a force of 0.3 N through a snap-through instability that is triggered after 0.2 s of electrical activation with an input power of 21.1 +/- 0.32 W (i.e., electrical energy input of 4.22 +/- 0.06 J. The consistency and robustness of the snap-through actuator response is experimentally validated through cyclical testing (580 cycles). The compact and fast-responding properties of the soft bistable actuator allow it to be used as an artificial muscle for shape-reconfigurable soft robots capable of multiple modes of SMA-powered locomotion. This is demonstrated by creating three soft robots, including a reconfigurable amphibious robot that can walk on land and swim in water, a jumping robot (multimodal crawler) that can crawl and jump, and a caterpillar-inspired rolling robot that can crawl and roll.