How a Soft Rod Wraps around a Rotating Cylinder

Area of Science:

• Physics
• Materials Science
• Soft Robotics

Background:

• Helical coils are essential in nature and technology, particularly for soft machines like artificial muscles and grippers.
• The stability of helical coils depends on material properties and system geometry.

Purpose of the Study:

• To investigate the morphologies formed by a flexible, heavy rod wrapping around a rotating rigid cylinder.
• To provide a physical understanding of ordered morphology in soft threads and rods.

Main Methods:

• Experimental observation of rod morphologies.
• Theoretical analysis using geometrically nonlinear Kirchhoff rod theory.
• Numerical simulations to rationalize experimental findings.

Main Results:

• Identified three distinct morphologies: tight coiling, helical wrapping, and no wrapping.
• Demonstrated that rod shape is governed by bending elasticity, gravity, and system geometry, even with friction.
• Provided a comprehensive physical model for the observed phenomena.

Conclusions:

• The study offers a fundamental understanding of how flexible rods form ordered structures.
• Findings have implications for bacterial motility and the design of soft robotic grippers.