#include <Servo.h>

Servo servo1;
Servo servo2;
Servo servo3;
Servo servo4;

unsigned long previousMillis;
const unsigned long interval = 10;   // 10 or 20 milliseconds are common values

float position = 0; // position of servo motor
int direction = 1;     // direction for servo motor
int runCount = 0;      // number of completed runs

void setup() 
{
  servo1.attach(4);
  servo2.attach(5);
  servo3.attach(6);
  servo4.attach(7);
}

void loop() 
{
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis >= interval && runCount < 1) // Continue only if runCount is less than 1
  {
    previousMillis = currentMillis;

    float step;
    step = (90.0 - fabs(90.0 - position)) / 90.0;
    step = 0.1 + (pow(step, 1.5) * 2);  // make a steep curve, with 0.1 as minimum
    
    if (direction > 0)
    {
      position += step;
      if (position >= 180.0)
      {
        position = 180.0;
        direction = -1;
        delay(10000);
      }
    }
    else
    {
      position -= step;
      if (position <= 0.0)
      {
        position = 0.0;
        direction = 1;
        delay(10000);
        runCount++;  // Increment the runCount after completing one full run
      }
    }
    int angle = int(position);
    servo1.write(angle);
    servo2.write(angle);
    servo3.write(angle);
    servo4.write(angle);
  }
}