Optimum Frequency for DC Motor Control

Other Hardware Motors, Mechanics, Power and CNC
1

My project will use analogWrite() to set the PWM duty cycle for my DC motor. There is minimum torque involved since the motor just has to spin a lightweight plastic hemispherical dome and the rotational speed will most likely be less than 60 RPM.. From the details of the analogWrite() function it seems like the set frequency is either 490 or 980Hz, but I think for most DC motors it should be around 10kHz (see here).

Should I adjust the PWM frequency for optimal DC motor behaviour (the quieter the better)? I've seen a library that abstracts the control of the PWM signal frequency but haven't tried it out yet.

2

If the motor is a small DC motor without reduction gearing you most definitely will not be
able to drive it as slow as 60rpm - its unlikely you can control a motor (open-loop) below about 5% of
full speed using PWM.

Small motors ideally want 16kHz or so PWM (ultrasonic also means no audible whining).
Bigger motors want lower frequencies ideally to reduce iron losses, 4kHz is about the minimum
frequency that's acceptable for motors I think. However you must use a PWM frequency that your
motor driver can cope with - slow H-bridges will not be happy with 16kHz and may get very hot.

3

Thanks Mark, but this code does seem to work OK - I'm just wondering if I need to adjust the frequency for best performance/lowest sound produced:

int potPin = A0;
int motorPin = 3;
int potValue = 0;
int motorValue = 0;

void setup() {
 Serial.begin(9600);
}

void loop() {
 potValue = analogRead(potPin);  
 motorValue = map(potValue, 0, 1023, 0, 255);
 analogWrite(motorPin, motorValue);  
 Serial.print("potentiometer = " );     
 Serial.print(potValue);
 Serial.print("\t motor = ");
 Serial.println(motorValue);
 delay(2);    
}
4

Who's Matt?

5

Oops. Corrected post.