SBOR: a minimalistic soft self-burrowing-out robot inspired by razor clams

Area of Science:

• Biomimetics and Robotics
• Soft Robotics
• Animal Locomotion

Background:

• The Atlantic razor clam (Ensis directus) exhibits a distinct burrowing-out behavior using its muscular foot.
• This motion differs from known downward burrowing strategies involving shell movements and foot dilation.
• Understanding this natural mechanism can inspire novel robotic designs for excavation.

Purpose of the Study:

• To investigate the burrowing-out mechanism of the Atlantic razor clam.
• To design and analyze a self-burrowing-out robot (SBOR) inspired by the razor clam's strategy.
• To characterize the factors influencing the robot's burrowing performance in sand.

Main Methods:

• Observation of Atlantic razor clam burrowing behavior.
• Design and fabrication of a soft robotic actuator using a fiber-reinforced silicone tube.
• Experimental characterization of the SBOR's burrowing-out performance by varying actuation parameters and sand density.
• Development of a soil mechanics-based model to predict burrowing behavior.

Main Results:

• Cyclic inflation and deflation of the SBOR successfully drove it out of vertically packed sand.
• Stride length was influenced by overburden pressure, pull-out resistance, and frictional resistance, initially increasing then decreasing.
• Burrowing speed decreased with increased sand relative density and varied with actuation pressure.

Conclusions:

• The SBOR effectively mimics the razor clam's upward burrowing strategy through simple axial extension and contraction.
• The observed burrowing behavior is explained by asymmetric resistant forces and the flowing nature of sand.
• Findings suggest clams utilize sand's natural stress gradient for upward burrowing, and downward burrowing may require asymmetry.