Unit 3 had been knocking and "shaking" when the robot proceeds.
At unit 4, I want to eliminate it.
The "shaking" Happens cause of the power of the motor control is not appropriate. (Too much or too little power)
Therefore, we review the method of calculating power.
Removed the switch block from the program, we try to change setting the wheels of the motor power further.
Two wheels become able to move frequently, it should become adaptable to move.

[Download] line tracer Unit 4
(Created in NXT software for education 2.0)

In addition, because there are individual differences in the sensor, please adjust the value of the block according to your own light sensor.

And here is the movie that the robot is running.
The knocking and shaking was made until now, finally disappeared.
It is a great success.

[Movie] running of Unit 4 movie (youtube)

And to supplement, I tried to create a diagram of the movement of only B-side of the tire of the robot.
The green line is the movement of the light sensor. Theoretically the robot could not make curve steeper than this.

I have added only the C side of the tire turned, and when both B and C were turned on.
Only subtly alter the ratio of the power of B and C, will be moved forward to the direction with all color. (Green -yellow- purple)