In this paper, we obtain feedback laws to asymptotically stabilize relative equilibria of mechanical systems with symmetry. We use a notion of stability ‘modulo the group action’ developed by Patrick [1992]. We deal with both
internal instability and with instability of the rigid motion. The methodology is that of potential shaping, but the system is allowed to be internally underactuated,
i.e., have fewer internal actuators than the dimension of the shape space
