Obstacle Avoiding Robot using AVR ATmega32 – Part I

Hi and Welcome All,

In this tutorial series I will show you how to make a simple obstacle avoiding robot using the xBoard v2.0 microcontroller board. xBoard v2.0 is well suited for developing small intelligent robots as it is compact in size, has four DC motor controller, can be programmed using USB Port and many other features. It is also very easy to learn and use. The xAPI, which is a set of C functions which makes complex programming tasks such as PWM ,LCD, Remote Control etc very easy for beginners. You can buy it from here

http://shop.extremeelectronics.co.in/product_info.php?cPath=23&products_id=111

Its design is open so if you don't want to buy the board you can make it yourself at home by the help of its schematic.

The Robo's Task

The task of our robo is simple. To move randomly in an area avoiding obstacles, that's it ! Though the task is simple, its a complete autonomous robot in itself. It has a brain which reads sensors and makes decisions and command the motors.

In the course of making the robot you will learn various basic techniques which will be of great use for your further projects.

Our Final Robot will look like this.

AVR ATmega32 Based Obstacle Avoiding Robot

The following Video Demo Shows the Robo in Action

The following Video was submitted by Mr. André Giovann

We thanks Mr. Giovann for sharing his experience!

Mechanical Construction

The robot is built around a high quality metal chassis which you can purchase from any robotics dealer. You can also buy it from our online store and we will appreciate your help. The robot is driven by two 200 RPM DC Gear motor. It uses differential drive system and has one castor wheel in the front. The wheels are directly coupled with the motors shaft.

The motors are mounted to the chassis by a nut provided in the shaft of the motor.

Differential Drive System with two back wheels and a front castor wheel

The xBoard v2.0 is mounted by using the mounting kit provided with xBoard v2.0. The mounting kit includes screws, nuts and standoffs. The xBoard v2.0 is so designed that its mounting holes are neatly aligned with the holes in chassis.

xBoard v2.0 is the brain of our robot.

xBoard v2.0 is Easy to Mount

 

Mounting xBoard v2.0 with screws.

 

Connecting Motor Wires

 

Just Plug and Play !

Differential Drive Explained

Differential drive is a drive system in which both motion and steering can be done by two set of powered wheels. In differential drive their is a set of LEFT wheels and a set of RIGHT wheels. Both are powered. It does not requires turning of front wheel for the steering like we steer car or bikes. To turn the vehicle (or robo) the LEFT and RIGHT wheels are rotated at "different" speeds. That's why its called differential drive. For example If the RIGHT wheels rotates faster than the LEFT wheels then the robot will turn towards LEFT.

For this robot we will use the following rotation of wheel for the steering and straight motion.

Motion	LEFT Wheel	RIGHT Wheel
Forward	Counter Clockwise	Clockwise
Backward	Clockwise	Counter Clockwise
Rotate LEFT	Clockwise	Clockwise
Rotate RIGHT	Counter Clockwise	Counter Clockwise

The following diagram explains robots differential drive in details

Differential Drive System

So moving and steering the robot is just the matter of controlling two DC motors. You can easily access DC motors from xAPI. The details are given here.

• http://xboard.extremeelectronics.co.in/Motor1.htm
• http://xboard.extremeelectronics.co.in/Motor2.htm

Once you go through the articles you know how to start a particular motor either in CW or CCW direction. Here MotorA will be the right motor and the MotorB will be the left motor. So the following code snippets does the job.

Move Robo Forward

MotorA(MOTOR_CW,255);	//Right Motor Moves Clockwise (CW) with Full Speed (255)
MotorB(MOTOR_CCW,255); //Left Motor Moves Counter Clockwise (CCW) with Full Speed (255)

Move Robo Backward

MotorA(MOTOR_CCW,255);	//Right Motor Moves Counter Clockwise (CCW) with Full Speed (255)
MotorB(MOTOR_CW,255); //Left Motor Moves  Clockwise (CW) with Full Speed (255)

Rotate Robo Left

MotorA(MOTOR_CW,255);	//Right Motor Moves Clockwise (CW) with Full Speed (255)
MotorB(MOTOR_CW,255); //Left Motor Moves  Clockwise (CW) with Full Speed (255)

Rotate Robo Right

MotorA(MOTOR_CCW,255);	//Right Motor Moves Counter Clockwise (CCW) with Full Speed (255)
MotorB(MOTOR_CCW,255); //Left Motor Moves  Counter Clockwise (CCW) with Full Speed (255)

I have explained the code here so it does not create confusion when the whole program (which is reasonably large)of the robot is presented to you.

To know more about the functions MotorA and MotorB please see their documentation here.

That's all folks for this part! Don't forget to post you comment and feedback.

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Proceed To Part II of This Tutorial >>