Background Material for Snake Robots

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The Mechanism of Locomotion in Snakes


1. Of the four main types of locomotion observed in snakes, three (serpentine, concertina and crotaline) can be elicited from the common grass snake (Tropidonotus natrix) by appropriate modification of the animal's environment.

2. Serpentine motion depends on three factors, (i) The body must be thrown into one or more curves each of which exhibits an increase of curvature when measured towards the head of the animal, (ii) Active muscular tension must develop in the axial muscles which lie on the same side of the body as that in which the curvature is increasing, (iii) The body must be subjected to at least three external resistances acting normally to the surface of the body. The propulsive force is the resultant of the reactions exercised by all these external resistances.

3. A snake cannot propel itself by serpentine movement along a straight or circular path. Under such conditions Tropidonotus progresses by concertina movements, the nature of which are described.

4. The muscular cycle of a snake exhibiting ‘crotaline’, or side-winding, movements is essentially the same as that during serpentine motion; the difference in the type of movement relative to the ground is due to a difference in the nature of the external resistances offered by the animal's environment. The mechanical principle of crotaline movement is, fundamentally, that of a caterpillar tractor.

5. Serpentine, concertina, and crotaline movements do not depend on active movements on the part of the ribs or scales. Rectilinear movement involving these structures has not been observed in Tropidonotus.

Developments in Snake Robot Modeling and Locomotion


Snake robots may one day play a crucial role in search and rescue operations and fire-fighting where it may either be too narrow or to dangerous for personnel to operate. Properties such as high terrainability, redundancy, and the possibility of complete sealing of the body of the robot, make snake robots very interesting for practical applications and hence as a research topic. During the last ten to fifteen years, the published literature on snake robots has increased vastly. However, no thorough review of the theory presented in this period regarding mathematical modeling techniques and locomotion of snake robots has been found. The purpose of this paper is to give such a review. Both purely kinematic models and models including dynamics are investigated. The choice of modeling method is linked to snake robot design characteristics and locomotion approach. Different approaches to biologically inspired locomotion are also discussed

Analysis and design of a multi-link mobile robot (Serpentine)


This paper is a study on dynamic behavior of a snake robot, called Serpentine robot, 2nd version (SR#2). The SR#2 is the latest version of snake robots developed at FIBO as a research platform for studying serpentine gaits. The gait is in form of sinusoidal curve, considered one of the most effectiveness crawling pattern in the natural world. The Active Cord Mechanism (ACM) assumption, initiated by Hirose, is implemented. The robot motion results from different joint torques and frictional reacting forces in each wheel. In this study, we proposed a modified serpeniod function with steering command to control the robot's direction. We also performed dynamic analysis using Kane's method. Holonomic constraints under frictional forces and nonholonomic constraints unders velocities were considered. We verified our algorithm for directional control on this Serpentine robot both simulation and experiment.

Gait kinematics for a serpentine robot


This paper considers the problem of serpentine, or snake-like, locomotion from the perspective of geometric mechanics. A particular model based on Hirose's active cord mechanism is analyzed. Using the kinematic constraints, we develop a connection, which describes the net motion of the machine as a function of variations in the mechanism's shape variables. We present simulation results demonstrating three types of locomotive gaits, one of which bears an obvious resemblance to the serpentine motion of a snake. We also discuss how these algorithms can be used to optimize certain inputs given the particular choice of physical parameters for a snake robot