title: rotating a quaternion on 1 axis?
body: <p>I have a model rotated by a quaternion. I can only set the rotation, I can't add or subtract from anything.  I need to get the value of an axis, and than add an angle to it (maybe a degree or radian?) and than re-add the modified quaternion.</p>
  
  <p>How can I do this? (answer on each axis).</p>