//...
# include <Servo.h>
Servo myServo;
//     float y = ((a * x) + b) * x) + c;

const float a = (-1.0 / 180);
const float b = 2;
const float c = 0;

const int feedbackPin = 14;

void setup() {
  myServo.attach(9);
  Serial.begin(9600);
}

/*
y = 
191.7609 + (3.237289 - 191.7609)/(1 + pow(x/92.42119), 4.382869);
d + (a - d) / (1 + pow(x / c, b));
*/

# include <math.h>

double fourPL(double x)
{
    return 191.7609 + (3.237289 - 191.7609) / (1 + pow(x / 92.42119, 4.382869));
}


void loop() {
  for (int x = 0; x <= 180; x++) {
    float y = fourPL(x);
    int servoPos = constrain(y, 0, 180);
    myServo.write(servoPos);
    Serial.print("x: ");
    Serial.println(x);
    Serial.print("servo Pos: ");
    Serial.println(servoPos);
    delay(10);
  }

  delay(500);

  for (int x = 180; x > 0; x--) {
    float y = fourPL(x);
    int servoPos = constrain(y, 0, 180);
    myServo.write(servoPos);
    Serial.print("x: ");
    Serial.println(x);
    Serial.print("servo Pos: ");
    Serial.println(servoPos);
    delay(10);
  }
}