9. MOVEMotor line follower 2

9.1. Adding obstacle detection: set up the distance sensor

Add code to use the distance sensor so that, if something blocks the track, the buggy will turn around and go back the other way.

Set up the buggy’s distance sensor.

distance_sensor = MOVEMotor.MOVEMotorDistanceSensors()

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9.2. Add obstacle detection: spin function

If the distance sensor detects an object within 10 cm of the sensor, the buggy needs to spin around on the track.

Define spin_from_obstacle(spin_time=800) so that the buggy spins on the spot. As the left motor goes forward, the right motor reverses.

Use a default parameter, spin_time=800, which will set the sleep time so that the buggy turns about 180 degrees (when the motor speed is the default of 1).

def spin_from_obstacle(spin_time=800):
    buggy.left_motor(MAXTURN)
    buggy.right_motor(-MAXTURN)
    sleep(spin_time)

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9.3. Add obstacle detection: spin time constant

Add the SPINTIME constant to the code with the other constants.

This will be passed to the spin_from_obstacle function to set the spin time.

SPINTIME = 800

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9.4. Add obstacle detection: add to the while True loop

Add code to the while True loop to detect any objects within 10cm and spin the buggy if so.

# check for obstacle and spin and go back
if distance_sensor.distance() < 10:
    spin_from_obstacle(SPINTIME)

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9.5. Version 2 Code for thin line following with obstacle detection

from microbit import *
import MOVEMotor


buggy = MOVEMotor.MOVEMotorMotors()
buggy.stop()
line_sensor = MOVEMotor.MOVEMotorLineSensors()
line_sensor.line_sensor_calibrate()
left_sensor_start = line_sensor.line_sensor_read('left')
right_sensor_start = line_sensor.line_sensor_read('right')
distance_sensor = MOVEMotor.MOVEMotorDistanceSensors()

CHANGETHRESHOLD = 40
MAXSPEED = 1
MINTURN = -1
MAXTURN = 1
MOTORTIME = 20
SPINTIME = 800

def follow_thin_line(drive_time=20):
    left_sensor = line_sensor.line_sensor_read('left')
    right_sensor = line_sensor.line_sensor_read('right')
    black_left = left_sensor + CHANGETHRESHOLD < left_sensor_start
    black_right = right_sensor + CHANGETHRESHOLD < right_sensor_start
    if not(black_left) and not(black_right):
        buggy.left_motor(MAXSPEED)
        buggy.right_motor(MAXSPEED)
    elif black_left and not(black_right):
        buggy.left_motor(MINTURN)
        buggy.right_motor(MAXTURN)
    elif black_right and not(black_left):
        buggy.left_motor(MAXTURN)
        buggy.right_motor(MINTURN)
    else:
        buggy.left_motor(MAXTURN)
        buggy.right_motor(-MAXTURN)
    sleep(drive_time)

def spin_from_obstacle(spin_time=800):
    buggy.left_motor(MAXTURN)
    buggy.right_motor(-MAXTURN)
    sleep(spin_time)

while True:
    follow_thin_line(MOTORTIME)
    # check for obstacle and spin and go back
    if distance_sensor.distance() < 10:
        spin_from_obstacle(SPINTIME)
    buggy.stop()
    sleep(10)

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Tasks

1. Try adding some obstacles on the track or just to the side of the track to see how well the buggy detects them.

2. Try adjusting the SPINTIME constant to see if better outcomes can be obtained when turning the the buggy away from obstacles. Use the A button to increase SPINTIME by 100 and the B button to decrease SPINTIME by 50.