Epicyclic Gearing

From Wikipedia: Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. … Epicyclic gearing systems also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears.

Built with D3.js.

<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html;charset=utf-8"/>
    <style type="text/css">

body {
  font: 300 13px "Helvetica Neue", Helvetica;
}

form {
  padding: 1em;
}

form, svg {
  position: absolute;
}

path {
  fill-rule: evenodd;
  stroke: #333;
  stroke-width: 2px;
}

.sun path {
  fill: #6baed6;
}

.planet path {
  fill: #9ecae1;
}

.ring path {
  fill: #c6dbef;
}

</style>
  </head>
  <body>
    <form>
      Frame of Reference:<br>
      <input type="radio" name="reference" id="ref-ring">
      <label for="ref-ring">Annulus</label><br>
      <input type="radio" name="reference" id="ref-planet" checked>
      <label for="ref-planet">Planets</label><br>
      <input type="radio" name="reference" id="ref-sun">
      <label for="ref-sun">Sun</label>
    </form>
    <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/d3@2.5.1/d3.js"></script>
    <script type="text/javascript">

var w = 960,
    h = 500,
    r = 80,
    x = Math.sin(2 * Math.PI / 3),
    y = Math.cos(2 * Math.PI / 3),
    speed = 4,
    start = Date.now();

var svg = d3.select("body").insert("svg:svg", "form")
    .attr("width", w)
    .attr("height", h)
  .append("svg:g")
    .attr("transform", "translate(" + w / 2 + "," + h / 2 + ")scale(.55)")
  .append("svg:g")
    .data([{radius: Infinity}]);

svg.append("svg:g")
    .attr("class", "ring")
    .data([{teeth: 80, radius: -r * 5, ring: true}])
  .append("svg:path")
    .attr("d", gear);

svg.append("svg:g")
    .attr("class", "sun")
    .data([{teeth: 16, radius: r}])
  .append("svg:path")
    .attr("d", gear);

svg.append("svg:g")
    .attr("class", "planet")
    .attr("transform", "translate(0,-" + r * 3 + ")")
    .data([{teeth: 32, radius: -r * 2}])
  .append("svg:path")
    .attr("d", gear);

svg.append("svg:g")
    .attr("class", "planet")
    .attr("transform", "translate(" + -r * 3 * x + "," + -r * 3 * y + ")")
    .data([{teeth: 32, radius: -r * 2}])
  .append("svg:path")
    .attr("d", gear);

svg.append("svg:g")
    .attr("class", "planet")
    .attr("transform", "translate(" + r * 3 * x + "," + -r * 3 * y + ")")
    .data([{teeth: 32, radius: -r * 2}])
  .append("svg:path")
    .attr("d", gear);

d3.selectAll("input[name=reference]")
    .data([r * 5, Infinity, -r])
    .on("change", function(d) { svg.data([{radius: d}]); });

d3.selectAll("input[name=speed]")
    .on("change", function() { speed = +this.value; });

function gear(d) {
  var n = d.teeth,
      r2 = Math.abs(d.radius),
      r0 = r2 - 8,
      r1 = r2 + 8,
      r3 = d.ring ? (r3 = r0, r0 = r1, r1 = r3, r2 + 20) : 20,
      da = Math.PI / n,
      a0 = -Math.PI / 2 + (d.ring ? Math.PI / n : 0),
      i = -1,
      path = ["M", r0 * Math.cos(a0), ",", r0 * Math.sin(a0)];
  while (++i < n) path.push(
      "A", r0, ",", r0, " 0 0,1 ", r0 * Math.cos(a0 += da), ",", r0 * Math.sin(a0),
      "L", r2 * Math.cos(a0), ",", r2 * Math.sin(a0),
      "L", r1 * Math.cos(a0 += da / 3), ",", r1 * Math.sin(a0),
      "A", r1, ",", r1, " 0 0,1 ", r1 * Math.cos(a0 += da / 3), ",", r1 * Math.sin(a0),
      "L", r2 * Math.cos(a0 += da / 3), ",", r2 * Math.sin(a0),
      "L", r0 * Math.cos(a0), ",", r0 * Math.sin(a0));
  path.push("M0,", -r3, "A", r3, ",", r3, " 0 0,0 0,", r3, "A", r3, ",", r3, " 0 0,0 0,", -r3, "Z");
  return path.join("");
}

d3.timer(function() {
  var angle = (Date.now() - start) * speed,
      transform = function(d) { return "rotate(" + angle / d.radius + ")"; };
  svg.selectAll("path").attr("transform", transform);
  svg.attr("transform", transform); // frame of reference
});

</script>
  </body>
</html>

Modified http://mbostock.github.com/d3/d3.js?2.5.0 to a secure url

https://mbostock.github.com/d3/d3.js?2.5.0