Robotic Arm in Processing

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I’ve been doing some pretty heavy reading and writing for the last few days, so I took some time “off” this afternoon to work on a mini project that I had been thinking of for awhile. I wanted to write a program in Processing that would allow me to choose points in the workspace of my actual robotic arm. The screenshot above shows the result so far.

If you download Processing and run the code below, you’ll see that the x and y values of the end of the arm print out on the screen under the code. My next step is to get these numbers to hover near the end of the arm as I’m moving it around. I’d also like to be able to put in joint constraints and have the reachable workspace of the robotic arm mapped out in a different color than the background, so I know what points I can use to drive the real robotic arm easily. Right now, the line segments representing the robotic arm just disappear when I get out of range! But that’s fun too.

Planar Robotic Arm Visualizer
 by Dustyn Roberts 20120622

float a1 = 198; // shoulder-to-elbow "bone" length from Solidworks (mm)
float a2 = 220; // elbow-to-wrist "bone" length from Solidworks (mm) - longer c bracket

boolean elbowup = false; // true=elbow up, false=elbow down

int Xoffset = 425;
int Yoffset = 425;

float theta1 = 0.0; // target angles as determined through inverse kinematics
float theta2 = 0.0;

float c2 = 0.0; // is btwn -1 and 1
float s2 = 0.0;

float joint1X;
float joint1Y;

float joint2X;
float joint2Y;

void setup() {

  size(850, 650, P3D);
  background(157, 6, 50);

void draw() {
  background(123, 82, 171);
  rotateX(PI); // make the y axis point up 
  translate(Xoffset, -Yoffset); // lower down the arm and move it to the middle so we can see it

  // figure out the joint angles needed to get to mouseX, mouseY position
  get_angles(mouseX-Xoffset, -mouseY+Yoffset);  
  //figure out the joint coordinates of joint1 to draw link 1
  line(0.0, 0.0, joint1X, joint1Y);
  line(joint1X, joint1Y, joint2X, joint2Y);
  // print out the x and y values of the end effector

// Given target(Px, Py) solve for theta1, theta2 (inverse kinematics)
void get_angles(float Px, float Py) {
  // first find theta2 where c2 = cos(theta2) and s2 = sin(theta2)
  c2 = (pow(Px, 2) + pow(Py, 2) - pow(a1, 2) - pow(a2, 2))/(2*a1*a2); // is btwn -1 and 1

  if (elbowup == false) {
    s2 = sqrt(1 - pow(c2, 2)); // sqrt can be + or -, and each corresponds to a different orientation
  else if (elbowup == true) {
    s2 = -sqrt(1 - pow(c2, 2));
  theta2 = degrees(atan2(s2, c2)); // solves for the angle in degrees and places in correct quadrant

  // now find theta1 where c1 = cos(theta1) and s1 = sin(theta1)
  theta1 = degrees(atan2(-a2*s2*Px + (a1 + a2*c2)*Py, (a1 + a2*c2)*Px + a2*s2*Py));

void get_xy() {
  joint1X = a1*cos(radians(theta1));
  joint1Y = a1*sin(radians(theta1));

  joint2X = a1*cos(radians(theta1)) + a2*cos(radians(theta1+theta2));
  joint2Y = a1*sin(radians(theta1)) + a2*sin(radians(theta1+theta2));


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