/* GNU AGPLv3 (or later at your option)
   see bottom for more license info */

/* spin thing that erin likes */
$fn = 500;

weight = "penny";
// weight = "608zz";
bearing = "608zz";
wall_thickness = 2;
_608zz_radius = 22;
penny_radius = 19.05 / 2;
penny_thickness = 1.52;
weight_radius = (weight == "penny") ? penny_radius : _608zz_radius;
bearing_radius = (bearing == "608zz") ? _608zz_radius : 1/0;
arms = 3;

module spin(weight_radius,
            arms,
            wall_thickness,
            bearing_radius) {
  bearing_holder_radius = bearing_radius + wall_thickness;
  weight_holder_radius = weight_radius + wall_thickness;

  circle(bearing_holder_radius);

  /*
   * imagine a right triangle with one point at the origin, at the
   * center of the spinning bearing holder, one point in the middle of
   * the weight holder, and one point at the center of a circle tangent
   * to the first two, called the joiner circle.
   * the radius of the joiner circle is the arithmetic average of the
   * weight holder and bearing holder.
   */
  joiner_radius = (bearing_holder_radius + weight_holder_radius) / 2;
  /* a: goes between the center of the weight holder and the center of
     the joiner circle. */
  a = joiner_radius + weight_holder_radius;
  /* b: length of the base, which goes along the x-axis between
     the origin and the center of the weight holder. */
  b = weight_holder_radius + bearing_holder_radius;
  /* c: goes between origin and joiner circle. */
  c = bearing_holder_radius + joiner_radius;

  /* A: angle at the origin, between the base and hypotenuse.
     it is calculated using law of cosines, given the lengths of
     all 3 sides of the triangle. */
  A = acos((pow(b, 2) + pow(c, 2) - pow(a, 2)) / (2 * b * c));
  /* find the center of the joiner circle */
  joiner_x = cos(A) * c;
  joiner_y = sin(A) * c;

  /* find the points where the circles meet */
  bearing_joiner_point = [cos(A) * bearing_holder_radius,
                          sin(A) * bearing_holder_radius];
  bearing_weight_point = [bearing_holder_radius, 0];
  /* C: angle between x-axis and line-segment between center of weight
     holder and center of joiner.
     it is calculated using law of cosines, given the lengths of
     all 3 sides of the triangle. */
  C = acos((pow(a, 2) + pow(b, 2) - pow(c, 2)) / (2 * a * b));
  weight_joiner_point = [b - cos(C) * weight_holder_radius,
                         sin(C) * weight_holder_radius];
  for(arm = [0 : arms - 1]) {
    rotate(arm * 360.0 / arms) {
      difference() {
        polygon([bearing_weight_point,
                 bearing_joiner_point,
                 weight_joiner_point]);
        translate([joiner_x, joiner_y]) {
          circle(joiner_radius); } }
      mirror(v = [0, 1, 0]) {
        difference() {
          polygon([bearing_weight_point,
                   bearing_joiner_point,
                   weight_joiner_point]);
          translate([joiner_x, joiner_y]) {
            circle(joiner_radius); } } }
      translate([weight_holder_radius + bearing_holder_radius, 0]) {
        circle(weight_holder_radius); } } } }

/*
  This file is part of 3d-printables.

  3d-printables is free software: you can redistribute it and/or modify
  it under the terms of the GNU Affero General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  3d-printables is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU Affero General Public License for more details.

  You should have received a copy of the GNU Affero General Public License
  along with challenge-bot.  If not, see <http://www.gnu.org/licenses/>.
*/