  var helper = new THREE.BoxHelper(box, 0xff0000);
                box.limit = WALL_LIMIT - helper.geometry.boundingSphere.radius;
            }

            function createSphere( n ) {

                var geom = new THREE.SphereGeometry(OBJ_SIZE, 6, 6);
                var material = new THREE.MeshLambertMaterial( { color: randColor(), shading: THREE.FlatShading  } );
                var sphere = new THREE.Mesh( geom, material );
                sphere.position.set(randPos(), randPos(), randPos(