Serial monitor printing out wrong value

Projects General Guidance
1

I have been working on the following code:

...
}
const float a = 204.0;
const float b = 176.0;
const float h = 306.0;
const float a_quadrat = a * a;
const float b_quadrat = b * b;
const float h_quadrat = h * h;

void setServo(int servo, int winkel) {
...
}

void loop() {

  //Startposition
  const float ThighStart = 140;
  float KneeangleStart = degrees(acos((a_quadrat + b_quadrat - h_quadrat) / (2.0 * a * b)));

  int Kneeangle = KneeangleStart;

  setServo(0, ThighStart);
  setServo(1, Kneeangle);

  if ( ThighStart == 140) {

    IK();
  }
}


void IK() {
  // P1: Startposition
  const float InitialX = 0.0;

  // P2: Endposition
  const float TargetX = 200.0;

  const float Radius = (TargetX - InitialX) / 2.0;

  float ThighStart;

  for (int X = 0 ; X <= 200; X += 10.0)

  {
    ThighStart = 140;
    float Y = sqrt(Radius * Radius - pow(X - Radius, 2));
    float c = sqrt(X * X + pow((h - Y), 2));
    float angle = degrees(atan2(X, (h - Y)));
    float c_quadrat = c * c;
    float cosB = (a_quadrat + b_quadrat - c_quadrat) / (2.0 * a * b);

    float Kneeangle = degrees(acos(cosB));

    ThighStart = ThighStart - angle;
  
    Serial.print("X=");
    Serial.print(X);
    Serial.print(", Y=");
    Serial.print(Y);

    Serial.print(", c = ");
    Serial.print(c);
    Serial.print(", cosB = ");
    Serial.print(cosB);
    Serial.print(", ThighStart = ");
    Serial.print(ThighStart);
    Serial.print(", Kneeangle = ");
    Serial.println(Kneeangle);
    setServo(0, ThighStart);
    setServo(1, Kneeangle);

    delay(1000);

  }
}

While observing the KneeAngle values:
for X = 190, it prints KneeAngle = 62.49 with c = 260.96 which is wrong. Because for X = 190 it should be instead: c = 280.81 and KneeAngle = 86.41.
How does this error occur and how can it be corrected?
All the other values seem correct, except this one.

2

Why?

3

i verified the values with the calculator

4

What about other values, besides 190?

5

they are correct

6

Even 191 is correct? Edit - never mind, I see it never gets that value, it increments by 10.

7

try

  for (long X = 0 ; X <= 200; X += 10)
8

Thanks for the help.
It worked (and the ,,verified" value I mentioned before was miscalculated)

Why did it not work before?

9

The integer calculation X*X overflows the limits of an int type for any integer over 181.

10

ah I see.

Big thanks again :slight_smile: