metodo yoyo

[ant_alt]

domanda semplice:
una volta avviato, come si blocca?

quello che vorrei ottenere è questo

on (rollOver) {
    import mx.transitions.Tween;
    import mx.transitions.easing.Regular;
    var up1:Tween = new Tween(up, "_y", Regular.easeOut, _root.up._y, _root.up._y-30, 50, false);
    var down1:Tween = new Tween(down, "_y", Regular.easeOut, _root.down._y, _root.down._y+30, 50, false);
    up1.onMotionFinished = function() {
        var upover:Tween = new Tween(up, "_y", Regular.easeOut, _root.up._y, _root.up._y-10, 50, false);
        var downover:Tween = new Tween(down, "_y", Regular.easeOut, _root.down._y, _root.down._y+10, 50, false);
        upover.onMotionFinished = function() {
            upover.yoyo();
            downover.yoyo();
        };
    };
}
on (rollOut) {
    var up2:Tween = new Tween(up, "_y", Regular.easeOut, _root.up._y, _root.up._y+30, 50, false);
    var down2:Tween = new Tween(down, "_y", Regular.easeOut, _root.down._y, _root.down._y-30, 50, false);
}