var fan = d3.select("svg").select("g")
var fan_box = fan.node().getBBox()

fan.attr("transform", "rotate(1)")
d3.interval(spin_fan, 20)

var fan_rotation = 1
function spin_fan() {
  fan_rotation += 5
  fan.attr("transform", "rotate(" + fan_rotation + " " + (fan_box.x + fan_box.width / 2) + " " + (fan_box.y + fan_box.height / 2) + ")")
}