A servo function for spaceship.codes.

servo.js

/**
 * Turns your ship to the given angle. Returns true when it is within
 * epsilon radians of the target angle and the angular velocity is zero.
 *
 * @param {Number} angle
 * @param {Number} [epsilon] Defaults to 0.001
 * @return {Boolean} True if the operation is complete
 */
var servo = function(angle, epsilon) {
  // Set a default value for epsilon
  if (!epsilon) {
    epsilon = 0.001;
  }
  // Get the maximum angular acceleration
  var prevTurn = turn();
  turn(1);
  var maxAngularAccel = accel().angular;
  turn(prevTurn);
  // Get the smallest angle we need to move from our current angle
  // to reach the target angle
  var diff = (pos().angular - angle) % (Math.PI * 2);
  if (Math.abs(diff - (Math.PI * 2)) < Math.abs(diff)) {
    diff -= Math.PI * 2;
  } else if (Math.abs(diff + (Math.PI * 2)) < Math.abs(diff)) {
    diff += Math.PI * 2;
  }
  // Get the angular distance needed to travel and the angular
  // distance needed to decelerate from the current angular velocity
  var dist = Math.abs(diff);
  var decelDist = Math.pow(vel().angular, 2) / maxAngularAccel;
  // If we are within epsilon of the target angle and we no longer
  // have any angular velocity, we are done
  if (Math.max(dist, Math.abs(vel().angular)) < epsilon) {
    turn(0);
  	return true;
  }
  // Calculate and set the new acceleration; if we don't have enough
  // distance to decelerate, slow down - otherwise speed up
  var a = 0;
  if (dist < decelDist) {
    a = -vel().angular;
  } else {
    a = vel().angular - diff;
  }
  turn(a / maxAngularAccel);
  return false;
}