4.0 KiB
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.
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.
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.
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.
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.
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).
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).
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!