Bạn dùng lệnh này:

var rotation : Quaternion;
var radius = Vector3(5,0,0);
var currentRotation = 0.0;
function Update()
{
currentRotation += Input.GetAxis("Horizontal")*Time.deltaTime*100;
rotation.eulerAngles = Vector3(0, currentRotation, 0);
transform.position = rotation * radius;
}

hoặc

timer += Time.deltaTime;
angle = timer;
this.transform.position = new Vector3 ((centerx + Mathf.Sin(angle) * rad), centery,((centerz + Mathf.Cos(angle) * rad)));