Recently I collected a broken hard drive to experiment on making a POV clock that I found on the web. After taking the hard drive apart, my first idea was to drive the stepper motor in the hard drive using Arduino. I looked around the web for writeup and tutorials about the principles of driving stepper motors. I particularly found this resource very useful: http://www.cs.uiowa.edu/~jones/step/. Reading this tutorial I found out the type of stepper motor the hard drive had, as there are couple of types of stepper motors available in the market. This hard drive had a Variable Reluctance Stepper Motor and the internal construction of it is like the figure below.
The motor has 4 pins, the common pin is usually connected to the positive power supply and the three other pins are required to be supplied negative voltage in a sequence to get the stepper motor moving. The logic is visualized in the figure below:
Now that I understood the logic of driving the motor, I wrote up the code for Arduino. The code uses 3 arduino digital pins in output mode (Pin 2,3,4) to drive the 3 coils of the stepper motor. However the arduino digital I/O pins does not produce enough current to drive the motor coils. Therefore power transistors or Darlington array chips (ULN2003 etc.) or H-Bridge motor drive chip (L293D etc.) are required to successfully drive the motor. For the experiment I used couple of regular NPN switching transistors (2N3904). These transistors yield quite low current (around 150-200mA), so I couldn't drive the motor beyond a certain speed. I wrote the code that will start spinning the motor at a lower speed and then gradually speed up. You can play with the steppingDealy value to control the speed of the motor.
Here is the arduino code:
int pinA = 2;
int pinB = 3;
int pinC = 4;
int steppingDelay = 100;
void setup() {
pinMode(pinA, OUTPUT);
pinMode(pinB, OUTPUT);
pinMode(pinC, OUTPUT);
digitalWrite(pinA, HIGH);
digitalWrite(pinB, HIGH);
digitalWrite(pinC, HIGH);
}
void loop() {
stepping(1);
delay(steppingDelay);
stepping(2);
delay(steppingDelay);
stepping(3);
delay(steppingDelay);
if(steppingDelay > 10)
{
steppingDelay--;
}
}
void stepping(int stage)
{
switch(stage)
{
case 1:
digitalWrite(pinA, LOW);
digitalWrite(pinB, HIGH);
digitalWrite(pinC, HIGH);
break;
case 2:
digitalWrite(pinA, HIGH);
digitalWrite(pinB, LOW);
digitalWrite(pinC, HIGH);
break;
default:
digitalWrite(pinA, HIGH);
digitalWrite(pinB, HIGH);
digitalWrite(pinC, LOW);
break;
}
}
Arduino sketch download:
StepperTest.pde (829.00 bytes)