B - Follow the Path

Assemble your robot like the picture - this time, plug both the left and right line sensors in!

Plug the left one in A, and the right into B.

Let's test both sensors so we know how they work.

Build the test program in the picture - can you guess what it will do?

On the other side of your activity mat, program your robot and slowly move the line sensor side to side across one of the lines.

What happens to the motors? Does it do what you expected?

We need to write a program using the two sensors that follows the black track.

Let's consider each of the possibilities in turn, as shown in the diagram:

A - Off the track completely - both sensors HI

B - Slightly off to the left of the track - left sensor HI, right sensor LO

C - Slightly off to the right of the track - left sensor LO, right sensor HI

D - on the track, both sensors LO

For case A, if the robot goes off the track we need to make it stop so it doesn't drive off forever!

Start your line following program by building the program in the picture.

We need to check if A is HI AND if B is HI at the same time - we can do this with an AND block, which you can find in the Operators menu.

For case B, we are slightly too far left, so we need to turn right to get back on the line.

Add some more blocks to check the sensors, and turn right if we are slightly to the left of the track.

There are some hint blocks if you need them!

For case C, we are too far right, so need to turn left to get back on the track.

Add some more blocks to your program to check the sensors and turn left if we need to!

There are some more hint blocks if you need them.

Finally, we need to check for case D - both sensors are LO so we are on the track, and just need to go forwards.

And some more blocks to your program to complete it, and test your robot on the track.

It should be able to make it all the way around on its own!

If you're robot keeps coming off the track, try increasing the amount it turns, or adding a small wait after the turn to make it turn even more.

Currently, if the robot goes off the path completely (or the path ends) it just stops.

It would be more useful if the robot tried to find the path again!

Change your program so that instead of stopping, the robot drives so that it might find the path again. You can make this as complex as you like!

Some ideas:

Reverse in a straight line

Drive forwards whilst sweeping left and right

Drive in increasing size squares (hard)

Drive in an increasing size spiral (v. hard!)