Biologically inspired soft robots make a lot of sense in many different scenarios, but as with any class of technology, they have their limitations. Among other things, these compliant structures can struggle to move at the same speed as their more rigid counterparts. To help speed up swimming, a team of researchers from North Carolina State University turned to another little inspiration from nature: the manta ray.
Looking at the fish makes sense. These shark cousins effectively fly through the water thanks to massive, wing-like pectoral fins. However, the researchers ended up naming them after a completely different animal. “Butterfly Bots” are credited for their resemblance to human hands performing the butterfly stroke [see: the above image].
Two versions of the robot were created. The former is designed specifically for speed, capable of moving 3.74 body lengths per second – a large increase compared to soft robots that struggle to move one body length in that time. A second designed for more control moves about 1.7 body lengths per second. In the first case, the design makes turning a problem. With the second, the team added a second actuator to rotate the robot by flapping one wing at a time.
“To date, swimming soft robots have not been able to swim faster than one body length per second, but marine animals – such as manta rays – can swim much faster and much more efficiently,” paper co-author Jie Yin, it said in a statement. “We wanted to use the biomechanics of these animals to see if we could develop faster, more energy-efficient soft robots. The prototypes we developed are working extremely well.”
The body flexes up and down using a pneumatic air tube, which in turn flexes the wings/fins, propelling the system forward. Yin adds, “Most previous attempts to develop flapping robots have focused on using motors to provide power directly to the wings. Our approach uses bistable wings that are passively driven by moving the central body. This is an important difference because it allows for a simplified design that reduces weight.”
The team says it is working on an autonomous, untethered version of the soft-swimming butterfly robot.