112 lines
4.0 KiB
Markdown
112 lines
4.0 KiB
Markdown
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# Line Following
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## Introduction @fullscreen
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Make a program to follow a line using the Color sensor and reflected light.
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## Step 1
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We are going to test and see if the reflected light is white (outside the line) or black (on the line), and drive our robot accordingly. Open the ``||logic:Logic||`` Toolbox drawer. From the **Conditionals** section, drag out an ``||logic:If then else||`` block onto the Workspace, and drop it into the ``||loops:forever||`` loop.
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```blocks
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forever(function () {
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if (true) {
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} else {
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}
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})
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```
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## Step 2
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Open the ``||logic:Logic||`` Toolbox drawer again. From the **Comparison** section, drag out ``||logic:0 < 0||`` comparison block onto the Workspace, and drop it into the ``||logic:if then else||`` block, replacing ``true``.
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```blocks
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forever(function () {
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if (0 < 0) {
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} else {
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}
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})
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```
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## Step 3
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Open the ``||sensors:Sensors||`` Toolbox drawer. From the **Color Sensor** section, drag out a ``||sensors:color sensor light||`` value block onto the Workspace, and drop it into the first slot of the ``||logic:0 < 0||`` comparison block, replacing the `0`.
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```blocks
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forever(function () {
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if (sensors.color3.light(LightIntensityMode.Reflected) < 0) {
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} else {
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}
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})
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```
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## Step 4
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If the value of the reflected light is greater than 40% (white or very light) then our robot is outside the line, and we should steer it to the left. In the ``||logic:0 < 0||`` comparison block, click the operator drop-down menu to change from ``<`` to ``>`` comparison, and change the compared value to `40` replacing `0`.
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```blocks
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forever(function () {
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if (sensors.color3.light(LightIntensityMode.Reflected) > 40) {
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} else {
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}
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})
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```
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## Step 5
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Open the ``||motors:Motors||`` Toolbox drawer. Drag out **2** ``||motors:tank large motors||`` blocks onto the Workspace, and drop one of them into the ``||logic:if||`` part, and the other into the ``||logic:else||`` part of the ``||logic:if then else||`` block.
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```blocks
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forever(function () {
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if (sensors.color3.light(LightIntensityMode.Reflected) > 40) {
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motors.largeBC.tank(50, 50)
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} else {
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motors.largeBC.tank(50, 50)
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}
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})
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```
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## Step 6
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In the first ``||motors:tank large motors||`` block in the ``||logic:if||`` clause, change the speed values of the motors from ``50%``, ``50%`` to ``5%``, ``15%``. This slows down the robot, and steers it to the left (because the **C** motor is driving faster than the **B** motor).
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```blocks
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forever(function () {
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if (sensors.color3.light(LightIntensityMode.Reflected) > 40) {
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motors.largeBC.tank(5, 15)
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} else {
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motors.largeBC.tank(50, 50)
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}
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})
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```
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# Step 7
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In the second ``||motors:tank large motors||`` block in the ``||logic:else||`` clause, change the speed values of the motors from ``50%``, ``50%`` to ``15%``, ``5%``. This slows down the robot, and steers it to the right (because the **B** motor is driving faster than the **C** motor).
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```blocks
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forever(function () {
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if (sensors.color3.light(LightIntensityMode.Reflected) > 40) {
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motors.largeBC.tank(5, 15)
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} else {
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motors.largeBC.tank(15, 5)
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}
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})
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```
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## Step 8
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Now, let’s download our program to the brick. Plug your @boardname@ into the computer with the USB cable, and click the blue **Download** button in the bottom left of your screen. Follow the directions to save your program to the brick. Attach a Color Sensor to Port 3 of your brick, and attach your brick to a driving base with large motors attached to Ports B and C. See the instructions for building a _Driving Base with Color Sensor Down_. Test your program by positioning your robot to the right of a dark, thick line and then let it drive!
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