Characterization and Evaluation of Screw-Based Locomotion Across Aquatic, Granular, and Transitional Media

TL;DR

This work addresses the challenge of multi-media screw propulsion for amphibious robots by integrating heat-sink-inspired, terra-mechanics, and non-Newtonian-fluid perspectives into a unified, principle-driven framework. Through comprehensive experiments across water, dry sand, wet sand, and saturated sand, it demonstrates that dominant design parameters are media-dependent: blade height governs granular propulsion while pitch governs aquatic propulsion, with aspect ratio providing a cross-media ranking tool. The study introduces derived parameters such as aspect ratio $\psi = \frac{\tan(\alpha)}{N B_H}$ and theoretical tip speed $v_{tip} = \omega_s R \sin(\alpha)$ to better predict performance. It also reveals a rolling locomotion mode that dramatically improves mobility in saturated sand, highlighting strategies for multi-media adaptability and suggesting future work on variable-speed drives and media-transition sensing to prevent stalling.

Abstract

Screw-based propulsion systems offer promising capabilities for amphibious mobility, yet face significant challenges in optimizing locomotion across water, granular materials, and transitional environments. This study presents a systematic investigation into the locomotion performance of various screw configurations in media such as dry sand, wet sand, saturated sand, and water. Through a principles-first approach to analyze screw performance, it was found that certain parameters are dominant in their impact on performance. Depending on the media, derived parameters inspired from optimizing heat sink design help categorize performance within the dominant design parameters. Our results provide specific insights into screw shell design and adaptive locomotion strategies to enhance the performance of screw-based propulsion systems for versatile amphibious applications.

Figures (8)

• Figure 1: The figure above shows the full spectrum of materials and their models. Starting from the lower left, fluids use classical models, including the Navier-Stokes equations, which describe mass transport of material through a control volume. Next in the upper left is the Terrain model that describes how cohesion and normal force impact shear. Next are solids, which include one of the operating modes of saturated sand, and finally, in the bottom right are non-Newtonian fluids that include a second operating mode where shear changes due to agitation.
• Figure 2: In Figure 2 are labeled drawings of a generic heat sink and a generic screw. The equations for optimizing heat transfer include the equation that defines the optimal spacing of the fins. These equations inspired a new way of thinking about screw parameters to create an improved intuition about performance using aspect ratio (geometry) and tip speed (mass transport).
• Figure 3: (a) Pitch angle ($\alpha$) is taken to the be the angle of attack of the screw (b) Blade height ($B_H$) is the distance between the inner circular housing and the tip of the blade (c) Number of starts ($N$) is the number of unique blades as seen from the front of the screw shell (d) Blade spacing ($d$) is the spacing between blades seen from a side view (e) Tip speed ($v_tip$) is the speed a fixed reference point moves on the blade when the screw shell is traveling
• Figure 4: (a) The configuration of the testbed for aquatic testing, using the aquatic adapter to keep electronics out of the water (b) The configuration for sand and wet sand testing, where the motor is integrated inline with the screw shell to give better stiffness metrics. (c) Saturated sand testing uses an identical setup to sand testing. (d) Rolling set up where linear movement of the screw is generated through rolling.
• Figure 5: (a) An example of medium being pushed to the side of the screw in an "lateral displacement" effect (b) An example of tunneling where the screw is buried within the sand (c) A screw failing due to material shear failure where the screw threads go from defined to undefined at the point of failure underneath the screw