CharacterController falls through or slips off moving platforms

// If you want to support moving platform rotation as well: private var activeLocalPlatformRotation : Quaternion; private var activeGlobalPlatformRotation : Quaternion;

function Update () {

 // Perform gravity and jumping calculations here
 ...

 // Moving platform support
 if (activePlatform != null) {
     var newGlobalPlatformPoint = activePlatform.TransformPoint(activeLocalPlatformPoint);
     var moveDistance = (newGlobalPlatformPoint - activeGlobalPlatformPoint);
     if (moveDistance != Vector3.zero)
             controller.Move(moveDistance);
     lastPlatformVelocity = (newGlobalPlatformPoint - activeGlobalPlatformPoint) / Time.deltaTime;

     // If you want to support moving platform rotation as well:
     var newGlobalPlatformRotation = activePlatform.rotation * activeLocalPlatformRotation;
     var rotationDiff = newGlobalPlatformRotation * Quaternion.Inverse(activeGlobalPlatformRotation);

     // Prevent rotation of the local up vector
     rotationDiff = Quaternion.FromToRotation(rotationDiff * transform.up, transform.up) * rotationDiff;

     transform.rotation = rotationDiff * transform.rotation;
 }
 else {
     lastPlatformVelocity = Vector3.zero;
 }

 activePlatform = null;

 // Actual movement logic here
 ...
 collisionFlags = myCharacterController.Move (calculatedMovement);
 ...

 // Moving platforms support
 if (activePlatform != null) {
     activeGlobalPlatformPoint = transform.position;
     activeLocalPlatformPoint = activePlatform.InverseTransformPoint (transform.position);

     // If you want to support moving platform rotation as well:
     activeGlobalPlatformRotation = transform.rotation;
     activeLocalPlatformRotation = Quaternion.Inverse(activePlatform.rotation) * transform.rotation; 
 }

}

function OnControllerColliderHit (hit : ControllerColliderHit) { // Make sure we are really standing on a straight platform // Not on the underside of one and not falling down from it either! if (hit.moveDirection.y < -0.9 && hit.normal.y > 0.5) { activePlatform = hit.collider.transform;
} }

/** Helps keeping charactercontroller entities nicely on the platform Needs a Collider set as trigger in the gameobject this script is added to works best if collider is bit smaller as platform but extends quite a lot (say .5m or so) above the platform, As the platform possibly already has a normal collider the easiest way is to add a GameObject to the platform, give it a trigger collider and add this script. The yOffset is the vertical offset the character should have above the platform (a good value to start with is half the y value of the Collider size). */ public class JKeepCharOnPlatform : MonoBehaviour {

 // helper struct to contain the transform of the player and the
 // vertical offset of the player (how high the center of the
 // charcontroller must be above the center of the platform)
 public struct Data {
     public Data(CharacterController ctrl, Transform t, float yOffset) {
         this.ctrl = ctrl;
         this.t = t;
         this.yOffset = yOffset;
     }
     public CharacterController ctrl; // the char controller
     public Transform t; // transform of char
     public float yOffset; // y offset of char above platform center
 };

 public float verticalOffset = 0.25f; // height above the center of object the char must be kept

 // store all playercontrollers currently on platform
 private Hashtable onPlatform = new Hashtable();

 // used to calculate horizontal movement
 private Vector3 lastPos;

 void OnTriggerEnter(Collider other) {
     CharacterController ctrl = other.GetComponent(typeof(CharacterController)) as CharacterController;

     // make sure we only move objects that are rigidbodies or charactercontrollers.
     // this to prevent we move elements of the level itself
     if (ctrl == null) return;

     Transform t = other.transform; // transform of character

     // we calculate the yOffset from the character height and center
     float yOffset = ctrl.height / 2f - ctrl.center.y + verticalOffset;

     Data data = new Data(ctrl, t, yOffset);

     // add it to table of characters on this platform
     // we use the transform as key
     onPlatform.Add(other.transform, data);
 }

 void OnTriggerExit(Collider other) {
     // remove (if in table) the uncollided transform
     onPlatform.Remove(other.transform);
 }

 void Start() {
     lastPos = transform.position;
 }

 void Update () {
     Vector3 curPos = transform.position;
     float y = curPos.y; // current y pos of platform

     // we calculate the delta
     Vector3 delta = curPos - lastPos;
     float yVelocity = delta.y;

     // remove y component of delta (as we use delta only for correcting
     // horizontal movement now...
     delta.y = 0f;

     lastPos =curPos;

     // let's loop over all characters in the table
     foreach (DictionaryEntry d in onPlatform) {
         Data data = (Data) d.Value; // get the data
         float charYVelocity = data.ctrl.velocity.y;

         // check if char seems to be jumping
         if ((charYVelocity <= 0f) || (charYVelocity <= yVelocity)) {
             // no, lets do our trick!
             Vector3 pos = data.t.position; // current charactercontroller position
             pos.y = y + data.yOffset; // adjust to new platform height
             pos += delta; // adjust to horizontal movement
             data.t.position = pos; // and write it back!
         }
     }
 }

}