Issue

I'm trying to put together a programmed robot that can navigate the room by reading instructions off signs (such as bathroom-right). I'm using the AlphaBot2 kit and an RPI 3B+.

the image processing part works well, but for some reason, the MOTION CONTROL doesn't work. I wrote a simple PID controller that "feeds" the motor, but as soon as motors start turning, the robot turns off.

iPWM = 20 # initial motor power in duty cycle
MAX_PWM = 100 
dt = 0.001 # time step

#PID PARAMETERS#
KP = 0.2
KD = 0.01
KI = 0.00005

targets = ['BATHROOM', 'RESTAURANT', 'BALCONY']

class PID(object):
    def __init__(self,target):
        
        self.target = target
        self.kp = KP
        self.ki = KI
        self.kd = KD 
        self.setpoint = 320
        self.error = 0
        self.integral_error = 0
        self.error_last = 0
        self.derivative_error = 0
        self.output = 0
        
    def compute(self, pos):
        self.error = self.setpoint - pos
        #self.integral_error += self.error * TIME_STEP
        self.derivative_error = (self.error - self.error_last) / dt
        self.error_last = self.error
        self.output = self.kp*self.error + self.ki*self.integral_error + self.kd*self.derivative_error
        if(abs(self.output)>= MAX_PWM-iPWM and (((self.error>=0) and (self.integral_error>=0))or((self.error<0) and (self.integral_error<0)))):
            #no integration
            self.integral_error = self.integral_error
        else:
            #rectangular integration
            self.integral_error += self.error * dt
        
        if self.output>= MAX_PWM-iPWM:
            self.output = MAX_PWM-iPWM
    
            
        elif self.output <= -MAX_PWM:
            self.output = iPWM - MAX_PWM
        return self.output
        



class MOTORS(object):
    
    def __init__(self,ain1=12,ain2=13,ena=6,bin1=20,bin2=21,enb=26):
        self.AIN1 = ain1
        self.AIN2 = ain2
        self.BIN1 = bin1
        self.BIN2 = bin2
        self.ENA = ena
        self.ENB = enb
        self.PA  = iPWM
        self.PB  = iPWM

        GPIO.setmode(GPIO.BCM)
        GPIO.setwarnings(False)
        GPIO.setup(self.AIN1,GPIO.OUT)
        GPIO.setup(self.AIN2,GPIO.OUT)
        GPIO.setup(self.BIN1,GPIO.OUT)
        GPIO.setup(self.BIN2,GPIO.OUT)
        GPIO.setup(self.ENA,GPIO.OUT)
        GPIO.setup(self.ENB,GPIO.OUT)
        self.PWMA = GPIO.PWM(self.ENA,500)
        self.PWMB = GPIO.PWM(self.ENB,500)
        self.PWMA.start(self.PA)
        self.PWMB.start(self.PB)
        self.stop()

    def forward(self):
        self.PWMA.ChangeDutyCycle(self.PA)
        self.PWMB.ChangeDutyCycle(self.PB)
        GPIO.output(self.AIN1,GPIO.LOW)
        GPIO.output(self.AIN2,GPIO.HIGH)
        GPIO.output(self.BIN1,GPIO.LOW)
        GPIO.output(self.BIN2,GPIO.HIGH)
    
    def updatePWM(self,value):
        if value<0:
            self.PA = iPWM+abs(value)
            self.PB = iPWM
            self.PWMA.ChangeDutyCycle(self.PA)
            self.PWMB.ChangeDutyCycle(self.PB)
        if value>0:
            self.PA = iPWM
            self.PB = iPWM+value
            self.PWMB.ChangeDutyCycle(self.PB)
            self.PWMA.ChangeDutyCycle(self.PA)
        if value ==0:
            self.PA = iPWM
            self.PB = iPWM
            self.PWMB.ChangeDutyCycle(self.PB)
            self.PWMA.ChangeDutyCycle(self.PA)
            
        GPIO.output(self.AIN1,GPIO.LOW)
        GPIO.output(self.AIN2,GPIO.HIGH)
        GPIO.output(self.BIN1,GPIO.LOW)
        GPIO.output(self.BIN2,GPIO.HIGH)
        
        
    
    def stop(self):
        self.PWMA.ChangeDutyCycle(0)
        self.PWMB.ChangeDutyCycle(0)
        GPIO.output(self.AIN1,GPIO.LOW)
        GPIO.output(self.AIN2,GPIO.LOW)
        GPIO.output(self.BIN1,GPIO.LOW)
        GPIO.output(self.BIN2,GPIO.LOW)

then I have the loop over the camera captures, where i identify the nearest sign and calculate his width and x coordiante of its center:

cx = int(x+w//2)

    if d<= 60:
        mot.stop()
        GPIO.cleanup()
dutyCycle = pid.compute(cx)
pwm = mot.updatePWM(dutyCycle)

Solution

It is probably not the software. Your power supply is not sufficient or stable enough to power your motors and the Raspberry Pi. It is a very common problem. Either:

Use separate power supplies which is recommended
Or Increase your main power supply and use some short of stabilization of power

What power supply and power configuration are you using?

Answered By - KZiovas

Friday, October 29, 2021

[SOLVED] Why does my program makes my robot turn the power off?

Issue

Solution