SunFounder PiCar-X Kit - Page 66

SunFounder PiCar-X Kit
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if gm_state == 'forward':
px.set_dir_servo_angle(0)
px.forward(px_power)
elif gm_state == 'left':
px.set_dir_servo_angle(offset)
px.forward(px_power)
elif gm_state == 'right':
px.set_dir_servo_angle(-offset)
px.forward(px_power)
else:
outHandle()
finally:
px.stop()
print("stop and exit")
sleep(0.1)
How it works?
This Python script controls a Picarx robot car using grayscale sensors for navigation. Here’s a breakdown of its main
components:
• Import and Initialization:
The script imports the Picarx class for controlling the robot car and the sleep function from the time
module for adding delays.
An instance of Picarx is created, and there’s a commented line showing an alternative initialization
with specific grayscale sensor pins.
from picarx import Picarx
from time import sleep
px = Picarx()
• Configuration and Global Variables:
current_state, px_power, offset, and last_state are global variables used to track and control
the car’s movement. px_power sets the motor power, and offset is used for adjusting the steering
angle.
current_state = None
px_power = 10
offset = 20
last_state = "stop"
• outHandle Function:
This function is called when the car needs to handle an ‘out of line’ scenario.
It adjusts the car’s direction based on last_state and checks the grayscale sensor values to determine
the new state.
def outHandle():
global last_state, current_state
if last_state == 'left':
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62 Chapter 4. Play with Python