How can i control the execution time of an engine?

Question

I'm building a little Car with 2 Engine, one L298N driver and a Raspberry pi 3. But i need the engine run during some specific seconds and then cleanup the GPIO and the engine stop. Why? Because i'm building an API then when i do the car go forward with my actual code the car go forward in an infinite loop and it doesn't accept other request until it finished the last request(go forward) but it won't happen because is an infinite loop.

My code for the car go forward is:

import RPi.GPIO as GPIO
import os
import time

ena = 18
in1 = 23
in2 = 24
enb = 19
in3 = 6
in4 = 5
GPIO.setmode(GPIO.BCM)

GPIO.setup(ena,GPIO.OUT)
GPIO.setup(in1,GPIO.OUT)
GPIO.setup(in2,GPIO.OUT)

GPIO.setup(enb,GPIO.OUT)
GPIO.setup(in3,GPIO.OUT)
GPIO.setup(in4,GPIO.OUT)

pwm_a = GPIO.PWM(ena,500)  
pwm_b = GPIO.PWM(enb,500) 

pwm_a.start(0)   
pwm_b.start(0)  
os.system('clear')


try:
        while True:
                GPIO.output(in1,False)
                GPIO.output(in2,True)
                GPIO.output(in3,False)
                GPIO.output(in4,True)
                pwm_a.ChangeDutyCycle(100)
                pwm_b.ChangeDutyCycle(100)


except KeyboardInterrupt:
        pwm_a.stop()
        pwm_b.stop()
        GPIO.cleanup()
        os.system('clear')
        print
        print("User finished the program")
        print
        exit()

Answer 1

When you run code in a while loop, the code is executed over and over again. However once you have set a GPIO or PWM, it stays set until you change it. There's no need to keep setting it and setting it forever.

So what you can do is set the GPIOs and PWMs to make your motor run, then just wait for however long you want it to run, then make the changes you need to stop the motor.

Here's an example. It starts the motor, waits five seconds, then stops it. It also stops the motor if the user presses CTRL+C -- I presume you want this since you wrote it into your original program. It does NOT do the other stuff you mention -- accepting requests. It just runs for 5 seconds, then stops. I also assume your code works perfectly as a basis -- which I can't test because I don't have the hardware.

import RPi.GPIO as GPIO
import os
import time

# GPIO pin defintions
ena = 18
in1 = 23
in2 = 24
enb = 19
in3 = 6
in4 = 5

# Configure GPIO pins
GPIO.setmode(GPIO.BCM)

GPIO.setup(ena,GPIO.OUT)
GPIO.setup(in1,GPIO.OUT)
GPIO.setup(in2,GPIO.OUT)

GPIO.setup(enb,GPIO.OUT)
GPIO.setup(in3,GPIO.OUT)
GPIO.setup(in4,GPIO.OUT)

pwm_a = GPIO.PWM(ena,500)  
pwm_b = GPIO.PWM(enb,500) 

pwm_a.start(0)   
pwm_b.start(0)  
os.system('clear')

# Start the motor running
GPIO.output(in1,False)
GPIO.output(in2,True)
GPIO.output(in3,False)
GPIO.output(in4,True)
pwm_a.ChangeDutyCycle(100)
pwm_b.ChangeDutyCycle(100)

# Wait five seconds
try:
    time.sleep(5)

# In case the user presses CTRL+C
except KeyboardInterrupt:
        print("User finished the program")

# If we get here, either five seconds has passed, or the user pressed CTRL+C.  Either way, stop the motor and clean up
pwm_a.stop()
pwm_b.stop()
GPIO.cleanup()
os.system('clear')

exit()