Introduction

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Since time immemorial science has developed and evolved based around the concepts of nature and its working. Some examples like learning flight from birds, ultrasonic communication of dolphins and bats, etc. Thus trotting down this path, getting motivated from snakes that have existed and evolved for millions of years, we were motivated to model and simulate a snake robot with its various gaits. A snake’s motion adaptability and maneuverability in its surroundings with a simple string-like motion makes it a good subject for research and development.

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Its slender and lithe figure makes it capable to be applied in non-structural fields like the inspection of a pipe, in rescue operations, “disaster zones” for monitoring, and during surgeries in medical operations. Snakes display their locomotion due to hundreds of short globe articulations, but due to the technical limitations in our technologies, we fully can’t replicate those movements mechanically. Naturally, snakes display four types of locomotion gaits: Serpentine, Rectilinear, and Cornering.

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Inspired and motivated by all the development in the field of snake robotics throughout the years, here snakes one natural and one artificial gait movement of snakes are researched and analyzed: Rectilinear and Side Winding locomotion respectively. First, a design and model of the robot using Solid Works, containing six degrees of freedom, six joints, and seven links was constructed. Secondly, the kinematics and dynamics of the snake robot, with its velocity, acceleration, and displacement relative to the center of gravity of the robot was analyzed. Thirdly, using V-REP simulation of the snake robot which is coded using the LUA script to obtain the two gait movements: Rectilinear and Side-Winding respectively were performed.

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3-D CAD Modelling

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The snake robot is designed and developed with six joints and seven links. While designing the model the orientation of the joints with their respective link lengths plays a major important role in determining the motion of the robot and its ability to maneuver in confined spaces. Additionally, the link lengths determine the stiffness of the mobile snake robot as with increasing link lengths stiffness of the snake robot and its ability to take turns or circle around spaces decreases.

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Each joint is a revolute joint and has one degree of freedom and is placed at an angle of 90 degrees to another. The type of end effector at the head of the robot will vary based on the type of application. For this project, the end effector will be a camera or any other sensory system like an infrared sensor or ultrasonic sensor.

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The 3D CAD model is built by fixing it to a base frame. The biggest advantage of this CAD model lies in its ability to add or remove individual snake segments on its body. Thus making the length of the snake robot longer or shorter based on specific applications and requirements of the robot. This best states the overall increased modularity and robustness of the system.

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The material defined for the snake robot is carbon fiber due to its high tensile strength with light weight. Each link has an inbuilt servo motor which is used to provide the necessary torque and force for the rotation of the robots around its joint.

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Forward Kinematics

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Forward kinematics establishes a relationship between the end effector and the base frame which is fixed in nature. Forward Kinematics is used to compute the position of the end-effector based on specified joint parameters. Denevet Hartenberg (DH) convention is used to assign the frames, computing the homogeneous matrix for the robot which is having six degrees of freedom.

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Inverse Kinematics

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The robot body is considered as a motion curve that it would execute during one cycle of its sidewinding gait where the points on the figure represent the joint distribution along the length of the snake robot. The Joint angles are obtained as the difference of tangent values of slopes of two consecutive links. 

 

 

Simulation using V-REP

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Virtual Robot Experimentation Platform (V-REP) is used as the simulation platform due to its elaborate APIs, various function, and features. In V-REP each object can be controlled individually with the use of plug-ins, embedded script, Robotic Operating System (ROS) node, or by the use of a remote API client. The controllers are coded using Lua programming language. Child script is used to write the simulation function.

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