INDIAN INSTITUTE OF TECHNOLOGY, GUWAHATI

EE304 – DESIGN LABORATORY

PROJECT REPORT

Modular Model of Snake Robot

Guide: Dr. Prithwijit Guha, Assistant Professor, IIT Guwahati

Name Roll No.

Swapnil Gupta 120108036

Somitra Baldua 120108034

Isht Dwivedi 120108045

Ankur Kunder 120102012

Ayush Pathania 120108047

Pawan Dixit 120102042

Introduction

Biological snakes occupy a wide variety of ecological niches, ranging from arid

desert to tropical forests as well as swimming in rivers and oceans. Their body

construction and locomotion technique has proved to be an extremely

effective and efficient strategy.

By attempting to build robots that emulate and perhaps match the capabilities

of their biological counterparts, it is possible that we will create useful tools

capable of carrying sensors, or surveillance operations by operating in

challenging environments where physical human presence is unfeasible or

impossible. Snake robots are robots inspired from biological snakes – in

structure, path trajectory and mechanism of movement.

Biological snakes have inspired a variety of robotic designs since 1920s. One of

the earliest Biomechanical studies of snakes was done by Shigeo Hirose, in

1970 who modelled a snake body as a continuous curve that could not move

sideways.

Serpenoid curve was first introduced by Hirose. This curve shows a path along

which a continuous snake has an optimal motion. The motor torques and

friction forces are minimum and smooth, so the power consumption is optimal.

According to his studies, the tangential angles of this path must be a sinusoidal

function. The continuous curve is defined such that any (x,y) point on the curve

satisfies:

where and are serpenoid parameters; different types of serpenoid curves

can be defined by varying them.

represents the position on the curve and the speed of motion can be defined

by the speed of changes in specifies undulation, periods and the

angular speed.

Different types of Serpenoid curves *

Based on similar mathematical formulations large varieties of snake models are

proposed. Innovative mechanical designs have flourished with one of the most

sophisticated being GMD- SNAKE 2 which has actuated joints between each

segment, along with powered wheels all around the circumference. This

enables an approximation of rectilinear progression, but such wheels may not

be effective on fibrous obstacles. In recent times to make the models more

adaptive, environment sensing tools are also used to make the design more

advance and robust.

(* Source: Paper named ‘ A Modified Serpenoid equation for snake robots’ by Dehghani, Mohammad, Center

for Mechatronics and Automation, School of Mechanical Engineering, Univ. of Tehran, Iran)

Challenges

The major challenge in this project was hardware construction.

As per the requirement of applications, in which this snake bot may be used, it

was decided to make this robot self-contained in terms of power and

computation, eliminate the drag effect of external factors and use transmitter-

receiver pair to interact with robot wirelessly.

Apart from that, mathematical analysis of 6 different reference frames all-

together (each attached to a module), software portion of the project that

involved controlling 6 servo motors to generate precise trajectory, and making

the snake move forward with all passive wheels – it was all together an

extremely challenging task.

Hardware Design

To keep the modules lightweight and torque requirement low -aluminum

sheets were used for its construction.

Laser cutting of these aluminum sheets were done in order to get the precise

shape of modules.

AutoCAD drawing of each module: Each module consist of 2 parts which were attached with each

other via clips made manually, using tin. The dimensions of the above module were all decided by

keeping in mind the size of servo motors, wheels and batteries to be used.

Metal gear standard servo motors of torque capacity 13.5kg/cm were used to

make the joints active.

Wheels, made from nylon, of 3.3cm diameter were used. (Lego wheels of 3cm

diameter were the most ideal choice, but due to unavailability we selected the

next best possible)

Batteries were added in order to make snake self-contained in terms of power.

Connection wires were soldered to batteries to avoid loose connections. Every

connecting wire either had an insulating covering or was covered properly to

avoid short circuiting.

All drilling work, construction of hinges (via clips), cutting of wheels and

Aluminum in proper and precise shape was done manually.

Top view of a single module

Side views of a single module

(Side view of two modules connected together)

Physical Parameters of the design:

Length of each module 14.5cm

width of each module 4.5cm

Height of each module 7.5cm

Radius of the wheel 3.3cm

Max. torque of the motor 13.5kg/cm at 6V

Arduino Mega is used as microcontroller. It is mounted on a separately

designed front module which is made three wheeled, in order to give stability

to the whole body.

MATHEMATICAL MODELLING OF SNAKE ROBOT

The snake robot is modelled as ball stick model which consists of n links

connected by n-1 joints.

The link is of mass mi, length 2*li and moment of inertia Ji (=mi* li3/3).

Symbols D and A stands for ‘difference’ and ‘addition’ operators respectively.

The vector e is the basis of kernel of D.

Consider the free body diagram of each link

fi is the friction force on the module, gi is the contact forces due to the adjacent

modules, ui is the torque due to joint forces and ti torque due to frictional

forces.

Position of each link in the Cartesian plane

The velocity components of the modules in the normal and tangential direction

Keeping ct and cn as the friction coefficients and dmi mass of the infinitely small

segment

Hence the torque and force due to friction is given by

Now these values we will use in the equation of motion

Equations of Motion

Translational motion

Rotational motion

Now x,y and angle are constrained by

Hence the translational velocity is given by

Decomposing the translational motion into two parts.

Serpenoid Curve

Angle between each segment with x-axis measured counter clockwise is

Hence

Relative angles that determine the shape of the discrete serpenoid curve

Undulatory motion of the snake can be imitated by changing the relative

angles of the snake robot in the following way

Software Design

The Arduino Mega2560 is a microcontroller board based on the ATmega1280. It

has 54 digital input/output pins (of which 14 can be used as PWM outputs), 16

analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator and a

USB connection. The board can operate on an external supply of 6 to 20 volts.

Zigbee is an Arduino compatible trans-receiver. It is long range high speed

serial wireless communication module which can give range of 30 meters

indoor or 100 meters outdoor. It is generally used for robot to robots or robots

to PC communication. It supports data rates of up to 115kbps.

One Zigbee module has been connected with Arduino Mega board to play the role

of signal receiver and mounted on the robot itself, to make the snake wireless.

One more Zigbee has been connected to laptop via interfacing board to play the

role of transmitter i.e. sending control signals from laptop to robot.

Assuming all the pre calculations have been done, Code for Arduino can be

written in a simple C language.

#include <Servo.h>

#include <math.h>

Servo myservo[8];

int pos = 0;

int i = 0;

int theta = 0;

void setup()

{

for(i = 0; i<8; i+=1)

{

myservo[i].attach(i+2);// put your setup code here, to run once:

}

}

void loop()

{

for(pos = 0; pos< 3.14;pos +=0.1)

{

for(i = 0; i<8; i+=1)

{

theta = 30*sin(pos*180/3.14 - 0.8*i);

//f(y<0) //

{

y = myservo[i].write(theta);

delay(15);

}

}

}

Conclusions: As targeted in challenges initially, the actual design try to

address all the desirable requirements of an ideal wireless snake robot upto a

certain extent.

The final design can be used as a base for testing and further researching in

path optimization, obstacle detection or even wireless power transfer over a

short range (by removing batteries and finding alternate method to power

servo motors)

Further improvements:

• Hardware of the robot can be improved, if better facilities are available

for its construction. Its shape can be made circular to provide a more

robust and overall covered body to the robot – hence making its

appearance closer to biological snakes.

• Its height can also be reduced, if smaller wheels are available.

• Aluminum Body can be completely covered with insulation to avoid any

chance of short circuit.

• There is an immense scope of improvement in Path planning, methods

of turning, speed of locomotion, energy efficiency and terrain

adaptability.

References:

• ‘Modelling, Analysis and Synthesis of Serpentine Locomotion with Multi-Link Robotic

Snake’ –By M.Saito, M.Fukaya and T.Iwasaki

• Introduction To Robotics : J.J Craig

• ‘ReBiS – Reconfigurable Bipedal Snake Robot’ –By Rohan Thakker, Ajinkya Kamat,

Sachin Bharambe, Shital Chiddarwar, and K. M. Bhurchandi

• ‘A Modular and Waterproof Snake Robot Joint Mechanism with a Novel Force/Torque

Sensor’ -By P. Liljebäck, K.Y. Pettersen , Stavdahl, J.T.Gravdahl

• ‘Sine-Wave Locomotion in a Robotic Snake Model Form and Programming’- By Mark

W Sherman

• 'A review on modelling, implementation, and control of snake robots'-By P. Liljebäck,

K.Y. Pettersen , Stavdahl, J.T.Gravdahla