I have been trying to run this 790kv BLDC motor using back EMF signals for commutation but I have been having issues after startup. It seems like I am getting some sort of misalignment between the actual motor position and where the arduino thinks the motor is. I used code from another forum post (shown below) but yet it seems to get stuck. Here is a video of it:
https://drive.google.com/drive/folders/1KteAuuL87zXT0W5_aSK2Taxkux9g-ZGE?usp=sharing
Here is the schematic it was inspired by:
The actual schematic: (note, some of the capacitor values listed in the schematic are not the same as the ones I actually used)
Code:
#define PWM_MAX_DUTY 255
#define PWM_MIN_DUTY 50
#define PWM_START_DUTY 100
byte bldc_step = 0, motor_speed, pin_state;
void setup()
{
DDRD |= 0xE0; // configure pins 5, 6 and 7 as outputs
PORTD = 0x00;
DDRB |= 0x0E; // configure pins 9, 10 and 11 as outputs
PORTB = 0x31;
// Timer1 module setting: set clock source to clkI/O / 1 (no prescaling)
TCCR1A = 0;
TCCR1B = 0x01;
// Timer2 module setting: set clock source to clkI/O / 1 (no prescaling)
TCCR2A = 0;
TCCR2B = 0x01;
// ADC module configuration
ADMUX = 0x60; // configure ADC module and select channel 0
ADCSRA = 0x84; // enable ADC module with 16 division factor (ADC clock = 1MHz)
PCICR = EIMSK = 0; // disable all external interrupts
pinMode(2, INPUT_PULLUP);
pinMode(3, INPUT_PULLUP);
pinMode(4, INPUT_PULLUP);
}
// pin change interrupt 2 (PCINT2) ISR
ISR (PCINT2_vect)
{
if( (PIND & PCMSK2) != pin_state )
return;
// BEMF debounce
for(byte i = 0; i < 20; i++)
{
if(bldc_step & 1){
if(PIND & PCMSK2) i -= 1;
}
else {
if(!(PIND & PCMSK2)) i -= 1;
}
}
bldc_move();
bldc_step++;
bldc_step %= 6;
}
// BLDC motor commutation function
void bldc_move()
{
switch(bldc_step)
{
case 0:
AH_BL();
BEMF_C_FALLING();
break;
case 1:
AH_CL();
BEMF_B_RISING();
break;
case 2:
BH_CL();
BEMF_A_FALLING();
break;
case 3:
BH_AL();
BEMF_C_RISING();
break;
case 4:
CH_AL();
BEMF_B_FALLING();
break;
case 5:
CH_BL();
BEMF_A_RISING();
}
}
void loop()
{
SET_PWM_DUTY(PWM_START_DUTY); // setup starting PWM with duty cycle = PWM_START_DUTY
int i = 5000;
// motor start
while(i > 100)
{
delayMicroseconds(i);
bldc_move();
bldc_step++;
bldc_step %= 6;
i = i - 20;
}
motor_speed = PWM_START_DUTY;
PCICR = 4; // enable pin change interrupt for pins PCINT23..16 (Arduino 0 to 7)
while(1)
{
ADCSRA |= 1 << ADSC; // start conversion
while(ADCSRA & 0x40); // wait for conversion complete
motor_speed = ADCH; // read ADC data (8 bits only)
if(motor_speed < PWM_MIN_DUTY)
motor_speed = PWM_MIN_DUTY;
SET_PWM_DUTY(motor_speed);
}
}
void BEMF_A_RISING()
{
PCMSK2 = 0x04; // enable Arduino pin 2 (PCINT18) interrupt, others are disabled
pin_state = 0x04;
}
void BEMF_A_FALLING()
{
PCMSK2 = 0x04; // enable Arduino pin 2 (PCINT18) interrupt, others are disabled
pin_state = 0;
}
void BEMF_B_RISING()
{
PCMSK2 = 0x08; // enable Arduino pin 3 (PCINT19) interrupt, others are disabled
pin_state = 0x08;
}
void BEMF_B_FALLING()
{
PCMSK2 = 0x08; // enable Arduino pin 3 (PCINT19) interrupt, others are disabled
pin_state = 0;
}
void BEMF_C_RISING()
{
PCMSK2 = 0x10; // enable Arduino pin 4 (PCINT20) interrupt, others are disabled
pin_state = 0x10;
}
void BEMF_C_FALLING()
{
PCMSK2 = 0x10; // enable Arduino pin 4 (PCINT20) interrupt, others are disabled
pin_state = 0;
}
void AH_BL()
{
PORTD &= ~0xA0;
PORTD |= 0x40;
TCCR1A = 0; // turn pin 11 (OC2A) PWM ON (pin 9 & pin 10 OFF)
TCCR2A = 0x81; //
}
void AH_CL()
{
PORTD &= ~0xC0;
PORTD |= 0x20;
TCCR1A = 0; // turn pin 11 (OC2A) PWM ON (pin 9 & pin 10 OFF)
TCCR2A = 0x81; //
}
void BH_CL()
{
PORTD &= ~0xC0;
PORTD |= 0x20;
TCCR2A = 0; // turn pin 10 (OC1B) PWM ON (pin 9 & pin 11 OFF)
TCCR1A = 0x21; //
}
void BH_AL()
{
PORTD &= ~0x60;
PORTD |= 0x80;
TCCR2A = 0; // turn pin 10 (OC1B) PWM ON (pin 9 & pin 11 OFF)
TCCR1A = 0x21; //
}
void CH_AL()
{
PORTD &= ~0x60;
PORTD |= 0x80;
TCCR2A = 0; // turn pin 9 (OC1A) PWM ON (pin 10 & pin 11 OFF)
TCCR1A = 0x81; //
}
void CH_BL()
{
PORTD &= ~0xA0;
PORTD |= 0x40;
TCCR2A = 0; // turn pin 9 (OC1A) PWM ON (pin 10 & pin 11 OFF)
TCCR1A = 0x81; //
}
void SET_PWM_DUTY(byte duty)
{
OCR1A = duty; // set pin 9 PWM duty cycle
OCR1B = duty; // set pin 10 PWM duty cycle
OCR2A = duty; // set pin 11 PWM duty cycle
}
It worked a couple times (out of around 20 attempts) but it is frustrating that it is not working consistently.
I read through all the code and thought this part was incorrect as when bldc_step is odd, the signal would be rising and should be only decrementing when its LOW and vice versa? Not sure though. When I changed this it still did not work (similar behavior as before).
if(bldc_step & 1){
if ((PIND & PCMSK2)) i -= 1; // Isn't it supposed to be : if (!(PIND & PCMSK2)) i -= 1;
}
else {
if (!(PIND & PCMSK2)) i -= 1; // Isn't it supposed to be : if ((PIND & PCMSK2)) i -= 1;
}
If the reason is due to a lot of motor noise, what can I do to fix it on a hardware or firmware level? Or is there something else at hand.
I've been working on this for a long time and hope to solve this issue.
Thank you.
NOTE: I have checked if the comparator is damaged by disconnecting PVDD and turning the motor manually. The arduino does receive signals from all 3 phases.