Add code driven animation

I've got a mecanim state machine set up for moving a RectTransform around and now I want to add a code generated animation on top of the animations played by mecanim but I can't get my head around it.

I'm trying to do this, but it doesn't do anything. It looks like it's being overwritten by the mecanim animation.

 void Update () {
 
         
         timeCounter += Time.deltaTime * speed;
 
         float x = Mathf.Cos(timeCounter) * width;
         float y = Mathf.Sin(timeCounter) * height;
         float z = 0;
 
 
 
         transform.position += new Vector3(x, y, z);
 
     }