  We investigate the critical points of Coulomb potential of point charges
placed at the vertices of a planar polygonal linkage. It is shown that, for a
collection of positive charges on a pentagonal linkage, there is a unique
critical point in the set of convex configurations which is the point of
absolute minimum.
  This enables us to prove that two controlling charges are sufficient to
navigate between any two convex configurations of a pentagonal linkage.
