hexapod master slave communication

Hexapod

Contents

1 Team Members

2 Mentor

3 Abstract

4 Advantages

5 Design

5.1 Material

6 Code for master slave communication

6.1 Master code

6.2 Slave Code

7 Progress so far

8 Plans ahead

9 Expenses incurred

10 Problems Faced

o 10.1 Problem 1: Heavy and Weak Bot

10.1.1 Modifications Made:

o 10.2 Problem 2: High current Requirement

10.2.1 Modifications:

Team Members

Digvijay Maheshwari

Prateek Kushwaha

Saurabh Kelkar

http://stab-iitb.org/wiki/Hexapod#Team_Members

http://stab-iitb.org/wiki/Hexapod#Mentor

http://stab-iitb.org/wiki/Hexapod#Abstract

http://stab-iitb.org/wiki/Hexapod#Advantages

http://stab-iitb.org/wiki/Hexapod#Design

http://stab-iitb.org/wiki/Hexapod#Material

http://stab-iitb.org/wiki/Hexapod#Code_for_master_slave_communication

http://stab-iitb.org/wiki/Hexapod#Master_code

http://stab-iitb.org/wiki/Hexapod#Slave_Code

http://stab-iitb.org/wiki/Hexapod#Progress_so_far

http://stab-iitb.org/wiki/Hexapod#Plans_ahead

http://stab-iitb.org/wiki/Hexapod#Expenses_incurred

http://stab-iitb.org/wiki/Hexapod#Problems_Faced

http://stab-iitb.org/wiki/Hexapod#Problem_1:_Heavy_and_Weak_Bot

http://stab-iitb.org/wiki/Hexapod#Modifications_Made:

http://stab-iitb.org/wiki/Hexapod#Problem_2:_High_current_Requirement

http://stab-iitb.org/wiki/Hexapod#Modifications:

Mentor

Husain Manasawala

Abstract

Hexapod is a 6 legged locomotive popular among robotics hobbyists. Robot hexapods range

from simple one-motor toys to advanced platforms with 12 or more servos. Hexapod is

controlled by a micro-controller which drives the servos. Once a simple Hexapod is made it

can then be modified to detect obstacles automatically and so on.

Advantages

The robot has Legs and NOT wheels and thus it can be used in terrains that are otherwise not

easily reachable. A Hexapod has no specific direction i.e. it can move in any direction.

Design

The center of the Bot will have a hexagon made of acrylic. This part of the Bot will have the

power source and the microcontroller. To this will be attached the six legs of the Bot. Each

Leg of the Bot will have two motors- one will be attached to the body [from here on referred

to as bodymotor] and the other will be attached to the leg piece that will rest on the ground

[from here on referred to as legmotor]. Thus each leg will have two degrees of freedom. The

material that we used was 4mm acrylic sheet.

Note: If you use two different kinds of servos, use the one with the higher torque as the

legmotor as it’ll get the maximum load.

Material

Acrylic Sheets

Servo motors [# 12]

Battery

Micro controller/s

General purpose PCB(s).

We used Arduino UNO boards as our microcontrollers. Since we are using 12 servo motors

[each servo requires a PWM signal to control and one board has only 6 PWM Pins], we use

two Arduinos and using I2C communication between them. Note that a servo motor runs only

between the voltage range 4.8-6.0 Volts. If you use a higher voltage as the source you need to

step down the voltage to the above range. This we did using IC7805. Since one IC can supply

only 1 Amp current we used twelve of them. The current supply of the source needs to be

checked as the Bot will need very high current [to the tune of 5-6 Amps].

The driver circuit is as follows:

http://stab-iitb.org/wiki/File:Hexagon.jpg

http://stab-iitb.org/wiki/File:Main_leg.jpg

http://stab-iitb.org/wiki/File:Legpeice.jpg

Once the Bot was ready, the next challenging task was to synchronize different legs of

different Arduinos. In the I2C method communication, we have to short the grounds of the

two Arduinos, connect the SCL and the SDI pins i.e. Pin Nos. A4 and A5, of the two

Arduinos. In this method, one of the microcontrollers becomes the Master and the other one

becomes Slave. The Slave’s clock is synced to the Master’s.

Gaits (ways to move) of Hexapod: Alternating tripod: 3 legs on the ground at a time.

Quadruped. Crawl: move just one leg at a time. We are using Quadruped method in which at

any time at least 4 legs touch the ground.

Code for master slave communication

Master code

#include <Servo.h>

#include <Wire.h>

#include<String.h>

Servo bodymotor[3];

Servo legmotor[3];

int rcvd=-1,inbyte=0,count=0;

int angle1,angle2,a1,flag=0;

byte x,y;

String input="";

void setup()

{

pinMode(12,OUTPUT);

pinMode(13,OUTPUT);

bodymotor[0].attach(3);

http://stab-iitb.org/wiki/File:Circuit_For_one_arduino.jpg

bodymotor[0].write(90);





legmotor[0].attach(9);

legmotor[0].write(180);





delay(2500);

Serial.begin(9600);

Wire.begin();

}

//----------------------------------------

void loop()

{

while(Serial.available()>1)

{

if(count==0)

{

input="";

count++;

}

if(count==1)

{

char c=Serial.read();

input+=c;

}

}

if(Serial.available())

{

char last=Serial.read();

input+=last;

count=0;

}

if(input=="sit")

{

sitstand();

delay(50);

}

else if(input=="twist")

{

twist();

}

else if(input=="move")

{

newmove();

}

else if(input=="turnc")

{

turn(0);

}

else if(input=="turna")

{

turn(1);

}

else

{

reset_bot(500);

}

delay(500);

}

//--------------------------------------------

void request(int c)

{

delay(c);

Wire.requestFrom(2,1);

while(Wire.available())

{

rcvd=Wire.receive();

}

}

//------------------------------------------------

void sending()

{

rcvd++;

byte x;

x=byte(rcvd);

Wire.beginTransmission(2);

Wire.send(x);

Wire.endTransmission();

}

//--------------------------------------------------

void reset_bot(int wait)

{







delay(wait);

}

//----------------------------------------------

void sitstand()

{//2050


x=byte(50);

Wire.send(x);

Wire.send(0);


delay(50);

sending();




request(500);

sending();




delay(1000);

Wire.requestFrom(2,1);


x=byte(4);

Wire.send(x);





delay(500);

rcvd=-1;

}

//----------------------------------------

void move(int a,int b)

{


x=byte(a);

y=byte(b);

Wire.send(a);


if(b==0)

{

angle1=110;

angle2=70;

}

else if(b==1)

{

angle1=70;

angle2=110;

}


delay(500);

sending();//0

request(500);

bodymotor[0].write(angle1);

sending();//2

request(500);


sending();//4

request(500);


sending();//6

request(500);


sending();//8

request(500);


sending();//10

request(500);


sending();//12

request(500);

sending();//14



request(1000);

sending();//16

reset_bot(500);

rcvd=-1;

}

//----------------------------------------------------------

void turn (byte sense)

{//6500

rcvd = 21;

byte z;

z=byte(20);


Wire.send(z);

Serial.println("a sent");

Wire.send(sense);

Serial.println("b sent");


if(sense==0)

{

angle1=120;

}

else if(sense==1)

{

angle1=60;

}

delay(500);

sending();


request(750);

sending();


request(750);

sending();


request(750);

sending();



request(750);

sending();



request(750);

sending();



request(750);

sending();




delay(1000);

rcvd=-1;

reset_bot(500);

}

//-------------------------------------------------------

void newmove()

{//6850


y=byte(40);

x=byte(0);

Wire.send(y);


delay(50);

sending();


request(500);

sending();


request(500);

sending();


request(500);

sending();


request(500);

sending();


request(500);

sending();


delay(800);


delay(500);


delay(500);


request(500);

sending();

request(500);

sending();

request(500);

sending();

request(500);

sending();

rcvd=-1;

reset_bot(500);

}

//-------------------------------

void twist()

{//3650

a1=90;


x=byte(60);

Wire.send(x);

Wire.send(0);


delay(50);

while(a1<135)

{

sending();

a1=a1+5;

bodymotor[0].write(a1);



delay(100);

rcvd--;

}

while(a1>45)

{

sending();

a1=a1-5;




delay(100);

rcvd--;

}

while(a1<90)

{

sending();

a1=a1+5;




delay(100);

rcvd--;

}

rcvd=-1;

}

Slave Code

#include <Servo.h>

#include <Wire.h>

Servo bodymotor[3];

Servo legmotor[3];

int

rcvd,a=0,b=0,z=0,angle11,angle12,angle21,angle22,angle01,angle02,a1,a2=90,c

ounter=0;

byte y;

void setup()

{

Serial.begin(9600);



delay(300);



delay(300);



delay(300);



delay(300);



delay(300);



delay(500);

Wire.begin(2);

Wire.onReceive(interpret);

Wire.onRequest(whattosend);

}

void loop()

{

delay(100);

}

void reset_bot(int wait)

{







delay(wait);

}

void whattosend()

{

int x=rcvd+1;

y=byte(x);

Wire.send(y);

}

void interpret(int howMany)

{

if(z==0)

{

while(Wire.available()>0)

{

a=Wire.receive();

b=Wire.receive();

if(b==0)

{

angle11=110;

angle12=70;

angle01=110;

angle02=70;

a1=120;

}

if(b==1)

{

angle01=70;

angle02=110;

angle01=70;

angle02=110;

a1=60;

}

}

z=1;

}

else if(z==1)

{

while(Wire.available())

{

rcvd=Wire.receive();

}

if (a==0)

{

switch(rcvd)

{

case 0:

{




break;

}

case 2:

{




break;

}

case 4:

{




break;

}

case 6:

{


break;

}

case 8:

{


break;

}

case 10:

{


break;

}

case 12:

{


break;

}

case 14:

{



delay(700);

break;

}

case 16:

{

reset_bot(500);

z=0;

break;

}

default:

{

Serial.println("Invalid input from Master");

break;

}

}

}

if (a==1)

{

if (rcvd==0)

{



}

else if (rcvd==2)

{



}

else if(rcvd==4)

{



}

else if(rcvd==6)

{


}

else if(rcvd==8)

{



}

}

if (a==2)

{

switch(rcvd)

{

case 0:

{


break;

}

case 2:

{


break;

}

case 4:

{


break;

}

case 6:

{


break;

}

case 8:

{


break;

}

case 10:

{


delay(500);


break;

}

case 12:

{



delay(700);

reset_bot(500);

z=0;

break;

}

default:

{

Serial.println("Invalid input from Master");

break;

}

}

}

if(a==20)

{

switch(rcvd)

{

case 22:

{



break;

}

case 24:

{



break;

}

case 26:

{



break;

}

case 28:

{


break;

}

case 30:

{


break;

}

case 32:

{


break;

}

case 34:

{




delay(1000);

reset_bot(500);

z=0;

break;

}

default:

{

Serial.println("Invalid receipt from master during turn");

break;

}

}

}

if(a==40);

{

switch(rcvd)

{

case 0:

{


break;

}

case 2:

{


break;

}

case 4:

{


break;

}

case 6:

{


break;

}

case 8:

{


break;

}

case 10:

{


break;

}

case 12:

{


break;

}

case 14:

{


break;

}

case 16:

{


break;

}

case 18:

{

reset_bot(500);

z=0;

break;

}

}

}

if(a==50)

{

switch(rcvd)

{

case 0:

{







delay(500);

break;

}

case 2:

{







delay(750);

break;

}

case 4:

{







delay(500);

z=0;

break;

}

}

}

if(a==60)

{

switch(rcvd)

{

case 0:

{

if(counter<9)

{

a2+=5;







counter++;

}

else if(counter<27 && counter>=9)

{

a2-=5;







counter++;

}

else if(counter<36 && counter>=27)

{

a2+=5;







counter++;

}

if(counter==36)

{

counter=0;

a2=90;

z=0;

}

break;

}

}

}

}

}

Progress so far

The Hexapod is ready. It currently has the codes to Sit and stand up on its own, twist, turn

(both clockwise and anticlockwise) about its axis, and move in the forward direction. The Bot

accepts the commands from the Serial Monitor. The following are the set of commands:

sit - Sit and stand

twist - Twist

turnc - Turn clockwise

turna - Turn anticlockwise

move - Move forward

Plans ahead

We plan to make the Bot remote controlled using RF modules. There are also plans to make

the power supply on-board once we find a suitably light battery. After the above are

complete, we plan to attach proximity sensors so as to enable the Bot to move on all terrains

and adjust according to the height of the ground. After all this is done, we’ll make the robot

climb stairs. And probably make it even autonomous sometime.

Expenses incurred

Problems Faced

Problem 1: Heavy and Weak Bot

http://stab-iitb.org/wiki/File:All_Expenses.jpg

We earlier made a Bot that looked like this:

http://stab-iitb.org/wiki/File:Prev.PNG

The Bot was fine as far as the functioning was concerned. But it was quite heavy and so the

motors could not take the load. Also due to too many bends and joints, it was not sturdy and

could not stand straight.

Modifications Made:

The Bot was minimized. Bodymotors were attached to the main body itself. One major

modification done was in the design of the leg piece so it could lift itself up even when down.

The current Bot looks like this:

http://stab-iitb.org/wiki/File:The_hexapod.jpg

Problem 2: High current Requirement

Since the Hexapod has 12 Servos, it draws really high current. We tried using different

regulators that could give high current. We started with LM-338 Steel Package and ended up

blowing up two of them. It did fine when checked with no load on the motors, but failed as

soon as it got load. We looked for other regulators as well but we either did not find them or

the available ones were too expensive. We also realised that we did not have a source that

could supply such high current.

Modifications:

We used 12 7805ICs for our twelve motors, i.e. one separate regulator for each Servo. Since

each can supply 1 Amp current, it works good. We currently use two BATTERY

ELIMINATORS each having maximum current limit of 5Amps.

http://stab-iitb.org/wiki/File:Leg_design.jpg

Complete with all the connections the Hexapod looks like this:

Video

YouTube Video Link

http://www.youtube.com/watch?v=k2IRliBELjg

http://stab-iitb.org/wiki/File:Complete_with_all_connections.jpg

hexapod master slave communication

Documents

invalid input

rcvd wire

int

source

input

request

hexapod

leg