Three.js: Rotate at center of an object

Question

I've modified this single spinning cube so that it contain 3 cubes in an Object3D

http://jsfiddle.net/VsWb9/1243/

In the above example it uses the first cube. I need it to rotate on a single axis at the exact center of the object.

The object3D code

  geometry = new THREE.CubeGeometry(50, 50, 50);
    material = new THREE.MeshNormalMaterial();
    mesh = new THREE.Object3D();
    mesh1 = new THREE.Mesh(geometry, material);
    mesh1.position.x = 50;
    mesh2 = new THREE.Mesh(geometry, material);
    mesh2.position.x = 100;
    mesh3 = new THREE.Mesh(geometry, material);

    mesh.add(mesh1);
    mesh.add(mesh2);
    mesh.add(mesh3);

    scene.add(mesh);

Here is the rotation

  mesh.rotation.x += 0.01;
  mesh.rotation.y += 0.02;

EDIT: Just to say that this is an example to demonstrate the problem, my actual code object contains many different sized shapes.

Answer 1

You may define the coordinates of the center.

mesh.position.set( center.x, center.y, center.z );
mesh.geometry.applyMatrix(new THREE.Matrix4().makeTranslation( -center.x, -center.y, -center.z ) );