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Dec
06

An Obstacle Avoiding Robot

An Obstacle Avoiding Robot

Objective

The objective of this project is to build an obstacle avoiding robot and apply it to measure the dimensions of a room. In this project, a robot is built such that it detects an obstacle on its path and makes a turning decision in order to avoid collision. And, on the way it records the number of tire rotations to calculate the total distance travelled.

Robot Platform

This project uses breadboard as the main chassis because it serves as a strong mechanical support as well as a circuit board for the wire connections. A breadboard stays on top of the assembled sets of gears, motors, and four wheels.

Microcontroller

An Arduino Duemilanove is used as the main electronic prototyping platform. An Arduino Duemilanove has Atmega 328 microprocessor, and has I/O support on board. And, it uses standard programming language in C to support the microprocessor.


Robot Movement Mechanism

The movement mechanism is designed such that a microprocessor controls an H-bridge driver circuit to control the dc motors. There are four wheels mounted for this robot. When two wheels at the left side turn forward and two wheels at the right side turn backward, the robot turns clockwise direction. Similarly, when the two wheels at the right side turn forward and the two wheels at the left side turn backward, the robot turns anti-clockwise direction.

Motor Shield Kit

In this project, the arduino motor shield kit is used instead of designing H-bridge driver circuit on breadboard to simplify the circuit design. In addition to this, it consumes less space on a breadboard as it fits exactly on top of an arduino board. However, using of the motor shield kit has increased the budget of this project.

For detail information on how to assemble motor shield kit, click here.

L293d Circuit and Specification:

The motor shiel shown above consists of two L293d chips which are used to drive the motors (two motors by each L293d chip). L293d is a quadruple high current half-H driver designed to provide bidirectional drive currents of up to 600mA at voltages from 4.5 V to 36V. Since four motors are used in this project, two L293d chips are required. Thus, the directions of a dc motor connected to 1Y, 2Y pins and another dc motor connected to 3y, 4y pins of L293d can be controlled from the input pins 1A, 2A, 3A, and 4A.

For example,  a dc motor connected to the pin 1Y and 2Y can be controlled by an arduino with the code shown below:

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int enablepin1=1; //pin 1
int motorpin2=2; //pin 2 (1A)
int motorpin7=7; //pin 7 (2A)
void setup () {
pinMode(enablepin1,OUTPUT);
pinMode(motorpin2,OUTPUT);
pinMode(motorpin7,OUTPUT);
digitalWrite(enablepin1,HIGH);
}
void loop() {
digitalWrite(motorpin2,LOW);
digitalWrite(motorpin7, HIGH); //turns clockwise
delay(1000);digitalWrite(motorpin2,HIGH);
digitalWrite(motorpin7,LOW);//turns anti-clockwise
delay(1000);
}

However, the code design becomes very simple by using the motor shiel kit because you just need to import AFMotor.h Library and design the code for forward, backward, right or left movement as shown below:

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#include AFMotor.h;
AF_DCMotor motor1(1);
AF_DCMotor motor2(2);
AF_DCMotor motor3(3);
AF_DCMotor motor4(4);
void setup() {
Serial.begin(9600);
motor1.setSpeed(200);
motor2.setSpeed(200);
motor3.setSpeed(200);
motor4.setSpeed(200);
}
void loop() {
gostraight();
delay(1000);
gobackward();
delay(1000);
makeright();
delay(1000);
makeleft();
delay(1000);
}
void gostraight() {
motor1.run(FORWARD);
motor2.run(FORWARD);
motor3.run(FORWARD);
motor4.run(FORWARD);
}
void gobackward() {
motor1.run(BACKWARD);
motor2.run(BACKWARD);
motor3.run(BACKWARD);
motor4.run(BACKWARD);
}
void makeright(){
motor1.run(FORWARD);
motor2.run(BACKWARD);
motor3.run(FORWARD);
motor4.run(BACKWARD);
}
void makeleft() {
motor1.run(BACKWARD);
motor2.run(FORWARD);
motor3.run(BACKWARD);
motor4.run(FORWARD);
}

Obstacle Sensor

Srf005 ultrasonic range sensor is used to detect obstacle in this project, which can detect objects in its path over a distance of 3cm-3m. The Echo Output pin is connected to the input pin of the arduino board. The Trigger Input pin is connected to the output pin of the arduino board. Triggering the Trigger Input pin emits an ultrasonic pulse and then waits for the returned echo reflecting off an object by the Echo Output pin and sends signal to a microprocessor. Thus, distance is calibrated by the microprocessor using the time taken by a pin to get a signal.

A table below shows the specification of srf005 sensor:

Voltage 5V
Current 30mA
Frequency 40KHz
Max Range 3m
Min Range 3cm
Sensitivity Detect 3cm diameter broom handle at d>3m
Input Trigger 10µS Min. TTL level pulse
Echo Pulse Positive TTL level signal, width proportional to range
Small Size 43mm x 20mm x 17mm height

The following code design is used for srf005 sensor:

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int echopin=2;
int trigpin=3;
unsigned long pulsetime =0;
unsigned long distance =0;
void setup() {
Serial.begin(9600);
pinMode (echopin,INPUT);
pinMode (trigpin,OUTPUT);
}
void loop() {
digitalWrite(trigpin,HIGH);
delayMicroseconds(50);
digitalWrite(trigpin,LOW);
pulsetime=pulseIn(echopin,HIGH);
distance=pulsetime/58;
Serial.println(distance);
delay(100);
}

Tire Rotation Counter Design (Circuit Design)

In the circuit shown above, Vout is high when the circuit is closed while it is low when the circuit is open. The value of Vout is read by a microprocessor to increment a rotation count.

Mechanical Design for Tire Rotation Counter

Here, the two wires meet when a rotation is complete, and thus the circuit is closed. And, the circuit is open when the two wires do not meet.

I designed the code for the tire rotation counter as shown below:

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int count_sensor=1;
int val=0,addr=0,count=0,adval=0,oldcount=0,newcount=1;
void setup() {
Serial.begin(9600);
pinMode(count_sensor,INPUT);
}
void loop() {
// need to increment the count just by 1 for 1 touch by the two wires,
// regardless of the time of being in contact !!
adval=digitalRead(count_sensor);//coun_sensor is read as 1 for closed circuit
if (adval==1) //two wires are in contact
{
oldcount++;
newcount=oldcount;
}
while(adval==0 && newcount==oldcount) { //two wires not in contact makes adval=0
count++;
newcount++;
}
Serial.println(count);
}

Consideration for calculating distance on the basis of number of tire rotation:

    Length of the robot=16.5cm
    Robot stops before = 10cm
    Total missing length=16.5cm +10cm = 26.5 cm
    Radius of a tire (r) = 3.5cm
    Number of tire rotation =n
    Distance covered by n rotation = (2 x pi x r x n) + 26.5 cm

Conclusion

In this project, the robot is built from scratch. The mechanical assembly kit for the robot platform can be bought from hobby store for those who do not like to build the robot from scratch, however, building the module without buying the platform kit saves money.  This  project has been successful in demonstrating this robot as an obstacle avoiding robot and distance measuring robot, however, with addition of few extra stuffs, this robot can be more useful. For instance, X-bee module can be added  in order to add data logging system remotely,  a camera module can be added for remote monitoring feature. In addition to these, a GPS module can be added for accurate distance measurement by using coordinate system. Anyone who would like to conduct possible developmental experiments are most welcome !!

4 comments

No ping yet

  1. Nat says:

    Good work..

  2. Alexis Design says:

    The project is impressive but the counter mechanism needs redesign. Nice reading.

  3. Alease Bisikirski says:

    This is a really great blog. Thx to the auther

  4. pulkit vijay says:

    thank u for giving me this source code

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