平滑不稳定的jquery动画

我有一个在父元素内部旋转和反弹的图像。我做得很好，预计轮换会有点困难。刚开始的几秒钟是平稳的，然后开始有点摇晃。

我该如何解决这个问题？

$.fn.bounce = function(options) {
    var settings = $.extend({
        speed: 10
    }, options);
    return $(this).each(function() {
        var $this = $(this),
            $parent = $this.parent(),
            height = $parent.height(),
            width = $parent.width(),
            top = Math.floor(Math.random() * (height / 2)) + height / 4,
            left = Math.floor(Math.random() * (width / 2)) + width / 4,
            vectorX = settings.speed * (Math.random() > 0.5 ? 1 : -1),
            vectorY = settings.speed * (Math.random() > 0.5 ? 1 : -1);
        // place initialy in a random location
        $this.css({
            'top': top,
            'left': left
        }).data('vector', {
            'x': vectorX,
            'y': vectorY
        });
        var move = function($e) {
            var offset = $e.offset(),
                width = $e.width(),
                height = $e.height(),
                vector = $e.data('vector'),
                $parent = $e.parent();
            if (offset.left <= 0 && vector.x < 0) {
                vector.x = -1 * vector.x;
            }
            if ((offset.left + width) >= $parent.width()) {
                vector.x = -1 * vector.x;
            }
            if (offset.top <= 0 && vector.y < 0) {
                vector.y = -1 * vector.y;
            }
            if ((offset.top + height) >= $parent.height()) {
                vector.y = -1 * vector.y;
            }
            $e.css({
                'top': offset.top + vector.y + 'px',
                'left': offset.left + vector.x + 'px'
            }).data('vector', {
                'x': vector.x,
                'y': vector.y
            });
            setTimeout(function() {
                move($e);
            }, 50);
        };
        move($this);
    });
};
$(function() {
    $('#wrapper li').bounce({
        'speed': 7
    });
});
$(function() {
    var $elie = $("img");
    rotate(0);
    function rotate(degree) {        
        $elie.css({ WebkitTransform: 'rotate(' + degree + 'deg)'});  
        $elie.css({ '-moz-transform': 'rotate(' + degree + 'deg)'});                      
        timer = setTimeout(function() {
            rotate(--degree);
        },30);
    }
});

JS FIDDLE