  We study the equilibrium positions of three points on a convex curve under
influence of the Coulomb potential. We identify these positions as
orthotripods, three points on the curve having concurrent normals. This relates
the equilibrium positions to the caustic (evolute) of the curve. The concurrent
normals can only meet in the core of the caustic, which is contained in the
interior of the caustic. Moreover, we give a geometric condition for three
points in equilibrium with positive charges only. For the ellipse we show that
the space of orthotripods is homeomorphic to a 2-dimensional bounded cylinder.
