A Biomimetic Method to Replicate the Natural Fluid Movements of Swimming Snakes to Design Aquatic Robots

Abstract

Replicating animal movements with robots provides powerful research tools because key parameters can be manipulated at will. Facing the lack of standard methods and the high complexity of biological systems, an incremental bioinspired approach is required. We followed this method to design a snake robot capable of reproducing the natural swimming gait of snakes, i.e., the lateral undulations of the whole body. Our goal was to shift away from the classical broken line design of poly-articulated snake robots to mimic the far more complex fluid movements of snakes. First, we examined the musculoskeletal systems of different snake species to extract key information, such as the flexibility or stiffness of the body. Second, we gathered the swimming kinematics of living snakes. Third, we developed a toolbox to implement the data that are relevant to technical solutions. We eventually built a prototype of an artificial body (not yet fitted with motors) that successfully reproduced the natural fluid lateral undulations of snakes when they swim. This basis is an essential step for designing realistic autonomous snake robots.

Continuum Robots: From Conventional to Customized Performance Indicators

“…Presumably, these data represent an optimized biomechanical solution that can be used as a standard with which the snake robot can be designed and actuated, acting as reference values for the geometric parameters previously defined. The snake vertebrae length and body profile were measured on two snake species ( Hierophis viridiflavus , Natrix helvetica ) [ 48 ] and used to size the snake robot vertebrae length and disk diameter. This provided the core data to shape the broad snake geometry.…”

“…Dead snakes were collected opportunistically, for example hit by vehicles (permit issued to XB, DBEC 004/2022). The measured data resulted in respective measurement intervals in which the snake robot skeleton was sized and designed [ 48 ], represented through elliptical vertebrae in a 3D plot ( Figure 3 ).…”

“…An equivalent beam model with a discrete number of elements (30 cylindrical segments, 40 mm length each, total backbone length 1200 mm) depicts the robot mechanical properties derived from the biological snake body deflections that were empirically measured [ 48 ] and numerically characterized as shown in Figure 3 . The equivalent beam section parameters that model each vertebra are identified with the Euler–Bernoulli beam theory of a large deflection non-linear elastic beam [ 49 ], expressed as where refers to second moment of area (in our case, for the circular section of an equivalent beam).…”

Continuum Robots: An Overview

“…Given the complexity of a continuum robot design, which often includes some elements that contribute to the overall stiffness but are almost impossible to model (e.g., power cables that are routed from the base of the robot to the end-effector through an inner channel), an experimental evaluation of the stiffness coefficient is often preferred, as for example reported in refs. [94,95].…”

Snake Robot with Motion Based on Shape Memory Alloy Spring-Shaped Actuators

“…As such, the size of this kind of implementation poses problems related to miniaturization and their application in narrow spaces [ 17 , 31 , 32 ]. The second class implements the use of DC motors that are not placed on the robot, where the force generated by the actuators is transmitted through the use of bands and pulleys that allow the robots to have low diameters such that they may be applied in narrow spaces [ 33 , 34 , 35 ]. However, the complexity of the control of this kind of actuation system is a main drawback, as the position of the joints is not directly related to the angular position of the motor shaft [ 36 , 37 ].…”