How to use Line Following

[ns280]

Hello,
I have a question. How can you code basic line following code for a spike prime robot. I tried the guide from the website (https://pybricks.com/ev3-micropython/examples/robot_educator_line.html) but it didn't work and it turns randomly.
Here is my code.

"""
Example LEGO® MINDSTORMS® EV3 Robot Educator Color Sensor Down Program
----------------------------------------------------------------------

This program requires LEGO® EV3 MicroPython v2.0.
Download: https://education.lego.com/en-us/support/mindstorms-ev3/python-for-ev3

Building instructions can be found at:
https://education.lego.com/en-us/support/mindstorms-ev3/building-instructions#robot
"""
from pybricks.hubs import PrimeHub
from pybricks.pupdevices import Motor, ColorSensor, UltrasonicSensor, ForceSensor
from pybricks.parameters import Button, Color, Direction, Port, Side, Stop
from pybricks.robotics import DriveBase, GyroDriveBase
from pybricks.tools import wait, StopWatch

# Initialize the color sensor.
line_sensor = ColorSensor(Port.B)


hub = PrimeHub()

# Initialize both motors. In this example, the motor on the
# left must turn counterclockwise to make the robot go forward.
left_motor = Motor(Port.C, Direction.COUNTERCLOCKWISE)
right_motor = Motor(Port.D)

# Initialize the drive base. In this example, the wheel diameter is 62.5mm (LEGO WHEELS).
# The distance between the two wheel-ground contact points is 136mm.
robot = GyroDriveBase(left_motor, right_motor, wheel_diameter=62.5, axle_track=136)

robot.settings(400, 800, 100, 200) 
Right_arm = Motor(Port.E, Direction.COUNTERCLOCKWISE, [12, 24, 12, 24])
Left_arm = Motor(Port.A, Direction.CLOCKWISE, [12, 24, 12, 48])

"""
#threshold calculator
while True:
    color = sensor.color()
    reflection = sensor.reflection()
    print (color, reflection)
"""

# Calculate the light threshold. Choose values based on your measurements.
BLACK = 15
WHITE = 100
threshold = (BLACK + WHITE) / 2

# Set the drive speed at 100 millimeters per second.
DRIVE_SPEED = 100

# Set the gain of the proportional line controller. This means that for every
# percentage point of light deviating from the threshold, we set the turn
# rate of the drivebase to 1.2 degrees per second.

# For example, if the light value deviates from the threshold by 10, the robot
# steers at 10*1.2 = 12 degrees per second.
PROPORTIONAL_GAIN = 1.2

# Start following the line endlessly.
while True:
    # Calculate the deviation from the threshold.
    deviation = line_sensor.reflection() - threshold

    # Calculate the turn rate.
    turn_rate = PROPORTIONAL_GAIN * deviation

    # Set the drive base speed and turn rate.
    robot.drive(DRIVE_SPEED, turn_rate)

    # You can wait for a short time or do other things in this loop.
    wait(10)

Please help.
Thanks,
NS280

[laurensvalk]

This looks quite good.

To start with, I would leave out the settings command that you've added.

When you try it, what doesn't work? Could you share a video perhaps?

[harikun77]

Removed the Drive settings as instructed and adjusted the proportional gain to 0.5. (Using the right sensor instead of left)...But with this method, the Bot is curving the left following the line but as noticed on the video, when the line curves to the right, the robot doesnt react and just goes straight...

from pybricks.hubs import PrimeHub
from pybricks.pupdevices import Motor, ColorSensor, UltrasonicSensor, ForceSensor
from pybricks.parameters import Button, Color, Direction, Port, Side, Stop
from pybricks.robotics import DriveBase, GyroDriveBase
from pybricks.tools import wait, StopWatch

# Initialize the color sensor.
line_sensorL = ColorSensor(Port.B)
line_sensorR = ColorSensor(Port.F)
hub = PrimeHub()

# Initialize both motors. In this example, the motor on the
# left must turn counterclockwise to make the robot go forward.
left_motor = Motor(Port.C, Direction.COUNTERCLOCKWISE)
right_motor = Motor(Port.D)

# Initialize the drive base. In this example, the wheel diameter is 62.5mm (LEGO WHEELS).
# The distance between the two wheel-ground contact points is 136mm.
robot = GyroDriveBase(left_motor, right_motor, wheel_diameter=62.5, axle_track=136)

Right_arm = Motor(Port.E, Direction.COUNTERCLOCKWISE, [12, 24, 12, 24])
Left_arm = Motor(Port.A, Direction.CLOCKWISE, [12, 24, 12, 48])

"""
#threshold calculator
while True:
    color = sensor.color()
    reflection = sensor.reflection()
    print (color, reflection)
"""

# Calculate the light threshold. Choose values based on your measurements.
BLACK = 15
WHITE = 100
threshold = (BLACK + WHITE) / 2

# Set the drive speed at 100 millimeters per second.
DRIVE_SPEED = 100

# Set the gain of the proportional line controller. This means that for every
# percentage point of light deviating from the threshold, we set the turn
# rate of the drivebase to 1.2 degrees per second.

# For example, if the light value deviates from the threshold by 10, the robot
# steers at 10*1.2 = 12 degrees per second.
PROPORTIONAL_GAIN = 0.5

# Start following the line endlessly.
while True:
    # Calculate the deviation from the threshold.
    deviation = line_sensorR.reflection() - threshold

    # Calculate the turn rate.
    turn_rate = PROPORTIONAL_GAIN * deviation

    # Set the drive base speed and turn rate.
    robot.drive(DRIVE_SPEED, turn_rate)

    # You can wait for a short time or do other things in this loop.
    wait(10)

IMG_0397.mov

[laurensvalk]

Could it be seeing the other things on the mat? It does appear to correctly curve right at first.

You may want to try the higher PROPORTIONAL_GAIN to at least confirm this is working. Perhaps also on a simpler board/line at first.

From here, though, it's not Pybricks-specific, just general robot challenges 😄