INDEX

SOME IMPORTANT THINGS ABOUT LINE FOLLOWERS WITH TWO SENSORS

1. The above circuits use switching OFF and ON the motor. This is not a good method because motor is basically an inductor. The time taken for the motor to attain full speed from OFF condition is too
much (ie in milliseconds depends on quality of motor). Suppose if we use two sensor for each side and when first sensor goes into black then motor speed will be 50% then the time required for a
motor to charge to full speed=time required to charge to 100% speed -time required to charge to 50%. But in the previous robots it is the time required to charge up to 100% speed. But this time is always in 10ms or more for charging up to 100% speed. I don't remember the charging and discharging equation of inductor. Do some calculation and see the difference. So the difference is above 10ms. This is a good time we are wasting.
2. Here we are stopping motor completely for a simple turn,so the time lost will be high. Think of a train going at 100kmph, which had to stop at a station for a 2sec. The time lost in its run will be around 7- 10sec, if it had stopped at a station compared to normal running of train. The same case with a robot motor stopped completely. So we should avoid this.
3. There are some switching time with power transistor, relays. The switching time of power transistor around .1ms while that of relay is about 100ms(not accurate,but greater than 10ms). So the time will be lost in the switching time of these components. So it is better not to use relays to drive motors. But if you are using big motors of high rating, then you can use relay because they will move at low speed. But the robots we make are so small, so we should try to avoid using relays in the circuits because of its switching speeds.
4. We require high speed devices. Motor switching speed cannot be controlled very much, because it is basically an inductor and we can do nothing to it except buying a costly motor. So here cost will
become high, if you go for good mechanical parts and motors. So let's think of reduced cost and good speeds. Instead of power transistor you can use MOSFET's speed around 100K(switching
speed). So it is better to use MOS than power transistor in motor driving circuitary.

5. Figure shows the motion of a normal robot

http://www.geocities.com/laosoh/robots/linefollow.htm. See from the site how the robot moves in different bendings. Here the blue line represents the path in which the robot has moved. You can see
for a small bend how much time it switched. So if you use a relay the time lost will be great will come around 2sec(or more) for a normal path. You can see that as the number of bends increases the time for the robot to cover increase. Suppose if the distance the robot has to move is of good length (suppose 5m), then the time lost will be around 10sec(or more). If your arena has only bends and having sharp bends with some cutting, then the time lost will be too much with the above circuits. The time will be number of switching*(s/w of transistor+relay+motor). This will come in minutes if you had to travel a path having irregular bends and of good length.