  Screw-based locomotion is a robust method of locomotion across a wide range
of media including water, sand, and gravel. A challenge with screws is their
significant number of impactful design parameters that affect locomotion
performance. One crucial parameter is the angle of attack (also called the lead
angle), which has been shown to significantly impact the performance of screw
propellers in terms of traveling velocity, force produced, degree of slip, and
sinkage. As a result, the optimal design choice may vary significantly
depending on application and mission objectives. In this work, we present the
Novel Actuating Screw Unit (NASU). It is the first screw-based propulsion
design that enables dynamic reconfiguration of the angle of attack for
optimized locomotion across multiple media and use cases. The design is
inspired by the kresling unit, a mechanism from origami robotics, and the angle
of attack is adjusted with a linear actuator. In contrast, the entire unit is
spun on its axis to generate propulsion. NASU is integrated into a mobile test
bed and experiments are conducted in various media including gravel, grass, and
sand. Our experiment results indicate a trade-off between locomotive efficiency
and velocity exists regarding angle of attack, and the proposed design is a
promising direction for reconfigurable screws by allowing control to optimize
for efficiency or velocity.
