Servo - November 2010

Figure 2

the “steering” tab of a move block. More on that later.

String or text variables are rarely used with the NXT since the only way to output text is on the small screen which usually isn’t accessible when a robot is in motion. String variables store text. For instance, a string variable might be “Hello World!” They’re rarely used, and when they are, it’s often for simple chat robots which interact with a user through text. With all that in mind, let’s get to the robots!

Revisiting the Line Follower

Last month, we made Eddie follow a line using one light sensor, and built an attachment to follow a line using two light sensors. This time, we’ll put that attachment to work! Let’s start by attaching it to the robot. For double light sensor attachment building instructions, see the October issue. Figure 1 shows Eddie with the double light sensor assembly attached. Note that it is in the lower of the two potential positions. This means the light sensor will be closer to the ground, thus giving us more accurate readings. Plug the left sensor into port 1, and the right sensor into port 2 (Figure 2). Now let’s talk programming logic.

Thinking Like a Robot

So, we’ve got Eddie set up with two light sensors. Now we just need to understand what to do with them.

• If your floor is light in color, find some dark tape. If it’s dark, find some light tape.

• Lay the tape out on the floor in a zig-zag pattern.

With two light sensors, we have several options for how we can follow the line: • We can put one light sensor on either side of the line, and have Eddie turn into the line when one of the sensors detects it.

In this article, we’ll be using the first of the listed options for following a line. As you’ll see, even though we’ve already narrowed down what we’re programming the robot to do, there are many different ways to program the robot to ultimately do the same thing!