42099: Technic Off-Roader: Obstacle Avoidance

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42099: Technic Off-Roader: Obstacle Avoidance

Make the truck drive around autonomously using sensors.

Selecting a sensor

This project will work with any sensor that can measure distance.

You can use the Color and Distance sensor as in this example, but you can also use the Ultrasonic Sensor or the Infrared Sensor. Mount the sensor somewhere on the front of your truck.

Main program

This program builds on the basic driving example. It makes the truck back up and turn when it detects an obstacle.

from pybricks.pupdevices import Motor, ColorDistanceSensor
from pybricks.parameters import Port, Direction, Stop
from pybricks.tools import wait

# Initialize the motors and sensor.
steer = Motor(Port.C)
front = Motor(Port.A, Direction.COUNTERCLOCKWISE)
rear = Motor(Port.B, Direction.COUNTERCLOCKWISE)
sensor = ColorDistanceSensor(Port.D)

# Lower the acceleration so the car starts and stops realistically.

# Find the steering endpoint on the left and right. The difference between them
# is the total angle it takes to go from left to right. The middle is in between.
left_end = steer.run_until_stalled(-200, then=Stop.HOLD)
right_end = steer.run_until_stalled(200, then=Stop.HOLD)

# We are now at the right limit. We reset the motor angle to the limit value,
# so that the angle is 0 when the steering mechanism is centered.
limit = (right_end - left_end)//2
steer.run_target(speed=200, target_angle=0, then=Stop.COAST)

# Given a motor speed (deg/s) and a steering motor angle (deg), this function
# makes the car move at the desired speed and turn angle. The car keeps moving
# until you give another drive command.
def drive(drive_motor_speed, steer_angle):
    # Start running the drive motors
    # Limit the steering value for safety, and then start the steer motor.
    limited_angle = max(-limit, min(steer_angle, limit))
    steer.run_target(200, limited_angle, wait=False)

# Keep driving.
while True:
    # Turn around if an obstacle is detected.
    if sensor.distance() <= 70:
        # Pivot a few times.
        for i in range(2):
            # Backward left.
            drive(-800, -90)
            # Forward right.
            drive(800, 90)
        # Otherwise just keep driving forward.
        drive(800, 0)