Exploration of drag reduction in soft robots - an Emperor Penguin inspired exit strategy

• Main Author: Thelen, Joanna
• Other Authors: Ranzani, Tommaso
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Engineering; Actuator; Air-water interface; Boundary layer; Bubbles; Buoyancy; Leap; Separation Point; Emperor penguins
• Online Access: https://hdl.handle.net/2144/42612

The rise of soft robots poses a promising revolution across a variety of fields, such as invasive surgical procedures or aquatic animal monitoring and sampling, by providing a softer solution to delicate problems. However, with their youth comes a need for growth, particularly in regard to increasing mobility in aquatic environments seeing as motion is often slow and belabored. Additionally, exit strategies in breaking the air-water interface are not thoroughly explored to date. To address these challenges, this study looks to bioinspiration for the answer in the form of Emperor Penguins. By utilizing microbubbles in their plumage to decrease drag forces on their bodies, Emperor Penguins are able to propel themselves out of the water to heights not theoretically achievable through buoyancy alone. Not only is the strategy highly effective, it lends well to the soft robotic field as pneumatic actuation is a commonly used mechanism of locomotion. To explore this behavior and simulate its effects, this study tests a hollow silicone ellipsoid with hole punctures applied to its surface for microbubble release. Bubble characteristics such as separation point, bubble diameter, and downstream bubble expansion were monitored when subjected to a fluid flow to determine ideal air pressure through the ellipsoid body. Drag reduction is tested by measuring the robot’s leap height out of the water.