A drawbot designed to use an arduino and 2 stepper motors to control the position of a marker and trace out a triangle.

The front was built to slant slightly backwards, with strings and spools mounted onto the motors above via epoxy and hot glue. Two pins were used to more accurately located where the string was when in was drawing on the paper, so that when programming the origin of the string could be set to to two corners of the paper. The pen was mounted on a wooden circle with three wheeled mounts forming a tripod around it to create stability. Spraypaint and duct-tape were added to add visual appeal.

Two motors were mounted to the back, one via screws and one via hot glue (due to a last minute error with the previously used motor and time constraints). The arduino and motor shield were hooked up together, with the arduino being fed 5V from a computer and the motor shield sourcing 12V to the motors. Reinforcements to the base were added on using hot glue.

The program defined the origin of the spools as the two pins on the board. A program was used that took a line and calculated the distance from a desired point, looks at the distance that the strings are currently, and steps up or down until the radius is within a desired range. The program would then increment the line to a point further up, and adjust the two spools accordingly. Our code used was derived from code written by Jason Schmidt.

#include <AFMotor.h>
#define Pi 3.14159
#define MAXSPEED1 420
#define MAXSPEED2 420

float R1, R2, radius, d;

AF_Stepper motor1(100, 1);
AF_Stepper motor2(48, 2);

void setup()
{
  R1 = 5.9424;
  R2 = 5.9424;
  radius = .25;
  d = 11;
  motor1.setSpeed(400);
  motor2.setSpeed(400);
  line1(5.5, -2.25, 8.8, -5.25);
  line1(8.8, -5.25, 10.35, -6.4);
  motor1.setSpeed(410);
  motor1.setSpeed(410);
  line2(10.35, -6.4, 6, -6.55);
  line2(6, -6.55, 3, -6.45);
  line1(3, -6.45, .45, -6.3);
  line1(.45, -6.3, 2.0, -5.4);
  line1(2.0, -5.4, 3.3, -4.25); 
  line1(3.30, -4.25, 5.5, -2.0); 
}

void line1(float x, float y, float x2, float y2)
{
  float t, r1, r2;
  for (t = 0; t < 1; t+=.00025)
  {
    r1 = sqrt((x + (x2-x)*t) * (x + (x2-x)*t) + (y + (y2-y)*t) * (y + (y2-y)*t));
    r2 = sqrt((x + (x2-x)*t - d) * (x + (x2-x)*t - d) + (y + (y2-y)*t) * (y + (y2-y)*t));
  
    if (abs(R1 - r1) > (2 * Pi * radius / 100))
    {
      if (R1 > r1)
      {
        motor1.step(1, FORWARD, SINGLE);
        R1 -= 2 * Pi * radius / 100;
      }
  
    else
    {
      motor1.step(1, BACKWARD, SINGLE);
      R1 += 2 * Pi * radius / 100;
    }
  }
  if (abs(R2 - r2) > (2 * Pi * radius / 48))
    {
      if (R2 > r2)
      {
        motor2.step(1, FORWARD, SINGLE);
        R2 -= 2 * Pi * radius / 48;
      }
  
    else
    {
      motor2.step(1, BACKWARD, SINGLE);
      R2 += 2 * Pi * radius / 48;
    }
   }
    }
    }

void line2(float x, float y, float x2, float y2)
{
  float t, r1, r2;
  for (t = 0; t < 1; t+=.0003)
  {
    r1 = sqrt((x + (x2-x)*t) * (x + (x2-x)*t) + (y + (y2-y)*t) * (y + (y2-y)*t));
    r2 = sqrt((x + (x2-x)*t - d) * (x + (x2-x)*t - d) + (y + (y2-y)*t) * (y + (y2-y)*t));
  
    if (abs(R1 - r1) > (2 * Pi * radius / 100))
    {
      if (R1 > r1)
      {
        motor1.step(1, FORWARD, SINGLE);
        R1 -= 2 * Pi * radius / 100;
      }
  
    else
    {
      motor1.step(1, BACKWARD, SINGLE);
      R1 += 2 * Pi * radius / 100;
    }
  }
  if (abs(R2 - r2) > (2 * Pi * radius / 48))
    {
      if (R2 > r2)
      {
        motor2.step(1, FORWARD, SINGLE);
        R2 -= 2 * Pi * radius / 48;
      }
  
    else
    {
      motor2.step(1, BACKWARD, SINGLE);
      R2 += 2 * Pi * radius / 48;
    }
  }

  }
}

Our team successfully completed the circle with no errors in 12 seconds!