Inverse Kinematics for a 2D Scara Robot

[finn433]

Hello, I am currently working on the inverse kinematics for my scara robot. This is the code and equation I use:

const double L1 = 202.25;
const double L2 = 193.35;

float alpha = 0;
float beta = 0;

void calc_IK(float x, float y){
  beta = acos((pow(x, 2)+pow(y, 2)-pow(L1, 2)-pow(L2, 2))/(2*pow(L1, 2)*pow(L2, 2)));
  alpha = atan((y/x)-atan((L2*sin(beta))/(L1+L2*cos(beta))));
  Serial.print("Beta: ");
  Serial.print(beta);
  Serial.print(" ");
  Serial.print("Alpha: "); 
  Serial.print(alpha);
  Serial.println(" ");
}

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

void loop() {
  calc_IK(3.0, 5.0);
  delay(500);
}

The equation itself works on paper but the code doesn't. I get for beta 1.57 and for alpha 0.73 instead of 89° and -88°. What am I missing?

[jremington]

In most programming languages, trigonometric functions operate on radians, not degrees. In C/C++ you have to perform the conversion in the code.

Instead of atan(), atan2() is usually preferred, as it correctly handles assignment of quadrants.