112 lines
4.0 KiB
Markdown
112 lines
4.0 KiB
Markdown
# Line Following
|
||
|
||
## Introduction @fullscreen
|
||
|
||
Make a program to follow a line using the Color sensor and reflected light.
|
||
|
||
|
||
|
||
## Step 1
|
||
|
||
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.
|
||
|
||
```blocks
|
||
forever(function () {
|
||
if (true) {
|
||
|
||
} else {
|
||
|
||
}
|
||
})
|
||
```
|
||
|
||
## Step 2
|
||
|
||
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``.
|
||
|
||
```blocks
|
||
forever(function () {
|
||
if (0 < 0) {
|
||
|
||
} else {
|
||
|
||
}
|
||
})
|
||
```
|
||
|
||
## Step 3
|
||
|
||
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`.
|
||
|
||
```blocks
|
||
forever(function () {
|
||
if (sensors.color3.light(LightIntensityMode.Reflected) < 0) {
|
||
|
||
} else {
|
||
|
||
}
|
||
})
|
||
```
|
||
|
||
## Step 4
|
||
|
||
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`.
|
||
|
||
|
||
|
||
```blocks
|
||
forever(function () {
|
||
if (sensors.color3.light(LightIntensityMode.Reflected) > 40) {
|
||
|
||
} else {
|
||
|
||
}
|
||
})
|
||
```
|
||
|
||
## Step 5
|
||
|
||
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.
|
||
|
||
```blocks
|
||
forever(function () {
|
||
if (sensors.color3.light(LightIntensityMode.Reflected) > 40) {
|
||
motors.largeBC.tank(50, 50)
|
||
} else {
|
||
motors.largeBC.tank(50, 50)
|
||
}
|
||
})
|
||
```
|
||
|
||
## Step 6
|
||
|
||
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).
|
||
|
||
```blocks
|
||
forever(function () {
|
||
if (sensors.color3.light(LightIntensityMode.Reflected) > 40) {
|
||
motors.largeBC.tank(5, 15)
|
||
} else {
|
||
motors.largeBC.tank(50, 50)
|
||
}
|
||
})
|
||
```
|
||
|
||
# Step 7
|
||
|
||
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).
|
||
|
||
```blocks
|
||
forever(function () {
|
||
if (sensors.color3.light(LightIntensityMode.Reflected) > 40) {
|
||
motors.largeBC.tank(5, 15)
|
||
} else {
|
||
motors.largeBC.tank(15, 5)
|
||
}
|
||
})
|
||
```
|
||
|
||
## Step 8
|
||
|
||
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!
|