  A finite-time attitude synchronization problem is considered in this paper
where the rotation of each rigid body is expressed using the axis-angle
representation. One simple discontinuous and distributed controller using the
vectorized signum function is proposed. This controller only involves the sign
of the state differences of adjacent neighbors. In order to avoid the
singularity introduced by the axis-angular representation, an extra constraint
is added to the initial condition. It is proved that for some initial
conditions, the control law achieves finite-time attitude synchronization. One
simulated example is provided to verify the usage of the control protocol
designed in this paper.
