74*245 Motor Driver

H-Bridge Driver

Simple PWM Gen.

Handy Method Measuring RPM

Measuring RPM via Photo reflector

Introduction to Robotic

DC, Stepper,and Servo Motor

Microcontroller Tutorial

Computer Interface
Tutorial
.............more links

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Desktop Line Following Robot

By : Elm-chan

Recently many kind of robot contests have being opened and some interesting reports of the challenge are found on the web. The Line Following is a kind of the robot contests to vie running speed on the line. I build a tiny line following robot which can run on the desk, moving the key board aside will do. It is for only a personal toy reduced its size less than one fifth compared to typical line following robots, not in formura. But I believe that it is suitable for home use in the small Japanese houses said that rabbit burrow. Of course I have also no time to take part in the robot contests.

About Line Follower

The line follower is one of the self operating robot that follows a line that drawn on the floor. The basic operations of the line following are as follows:

Capture line position with optical sensors mounted at front end of the robot. Most are using several number of photo-reflectors, and some leading contestants are using an image sensor for image processing. The line sensing procss requires high resolution and high robustness.
Steear robot to track the line with any steearing mechanism. This is just a servo operation, any phase compensation will be required to stabilize tracking motion by applying digital PID filter or any other servo argolithm.

Control speed according to the lane condition. Running speed is limited during passing a curve due to friction of the tire and the floor.

There are two line styles, white line on the black floor and black line on the white floor. Most contest are adopting the first one in line width of between 15 and 25 millimeters.

Hardware

Mechanics
Right image shows bottom view and side view of the built line following robot. All mechanical and electrical parts are mounted on a proto board, and it also constitutes the chasis.The line following robot is upheld in three points of two driving wheels and a free wheel. The driving wheels are made with a 7 mm dia ball bearing and a rubber tire. The free wheel is a 5 mm dia ball bearing attached loosely. To drive driving wheels, two tiny vibration motors that used for cellular phone, pager or any mobile equipment are used. Its shaft is pressed onto the tire with a spring plate, the output torque is transferred to the wheels.

The steearing mechanism is realized in differential drive that steear the robot by difference in rotation speed between the left wheel and the right wheel. It does not require any additional actuator, only controling the wheel speed will do.

Electronics

An Atmel ATmega8 is used for the controller and it is powered by a lithium coin cell. The other lithium coin cell is for only motors. Separating the power supply into two cells is to avoid accidental reset of the microcontroller due to voltage dip by motor start current. Six photo-reflectors are mounted at front end of the chasis. They sense reflection rate of the floor under them. Motors are driven in PWM to control rotation speed lineary. The latest circuit diagram is here.

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