SunFounder PiCar-S, Руководство пользователя

Страница: 56 / 85

SunFounder PiCar-S
Functions Explanation
ua = Ultra_Sonic.UltraSonic_Avoidance(17)
Create an object ua of a UltraSonic_Avoidance class in the Ultra_Sonic module. The number in the round bracket is
the initial parameter, which represents the pin number the SIG of the module is connected to. Since the BCM naming
method is applied, the corresponding pin on the Raspberry Pi is #17.
back_distance and turn_distance , two constants are to set the thresholds of the ranging distance.
while()
loop
When the detected distance is less than the back_distance , the car will move backwards; when it is between
back_distance and turn_distance , the car will turn a direction (you can set the turning angle in the aforementioned
parameter turning_angle and the angle can be a positive or negative number, for turning left or turning right respec-
tively; NOTE that the number of the turning angle should be -90 to 90 considering the servo’s max rotation degrees,
or the servo may be burnt.); when the detected distance is greater than the turn_distance , the car will keep moving
forward.
bw.backward() , making the rear wheels rotate backwards; bw.forward() , making the rear wheels spin forward. These
two functions in the rear wheel driving module back_wheels are to set the wheel’s rotating direction.
bw.set_speed(speed) , function in the back_wheels, to set the wheel’s rotating speed. The larger the number (within
the range 0-100) is, the faster the wheel rotates.
fw.turn(angle) , function in the back_wheels, to set the turning angle. The angle is 90 when the car moves straight
forwards; reduce the number to turn left, and increase it to turn right.
52 Chapter 1. About the PiCar-S