A Multigait Stringy Robot with Bi-stable Soft-bodied Structures in Multiple Viscous Environments

The exploration of spatially limited terrestrial or aquatic environments requires miniature and lightweight robots. Soft-bodied robot research is paving ways for a new class of small-scale robots that can navigate a variety of environments with minimum influence on the environment itself. However, it is generally challenging to design miniature soft-bodied robots that efficiently adapt to the change between viscous environments. A small-scale soft-bodied robot, which could slowly move on dry land, will need rapid motions to be able to swim in a wet environment. Although using snap-through buckling of a deformable body could help to create swift motions of the robot, merely applying the snap-through buckling does not improve the swimming speed of the robot so much. Here we propose a design of a stringy soft-bodied robot that can crawl on dry surfaces and swim in liquid environments. Besides taking advantage of the snap-through buckling using coil shape memory alloys (SMAs), we design the body of the robot with a geometrical overlapping of the active body segments and control the frequency of the undulation movement, which is crucial for the swimming locomotion. We evaluate the performance of the robot in different density and viscosity liquids such as cooking oil and Glycerin solution. We found that the robot needs to drastically change its undulation from low to high frequency when it moves from high to low viscosity environments. Our robot can swim at a speed of 3. 37 body-lengths per minute (BL/min) and crawl at a speed of 1. 74 BL/min. We anticipate our findings will help shed light on the design of soft-bodied robots that adapt to the changing environments efficiently.