On non-holonomic systems and variational principles
  We consider the compatibility of the equations of motion which follow from d'Alembert's principle in the case of a general autonomous non-holonomic mechanical system in N dimensions, with those equations which follow for the same system by assuming the validity of a specific variational action principle, in which the non-holonomic conditions are implemented by means of the multiplication rule in the calculus of variations. The equations of motion which follow from the principle of d'Alembert are not identical to the equations which follow from the variational action principle. We give a proof that the solutions to the equations of motion which follow from d'Alembert's principle do not in general satisfy the equations which follow from the action principle with non-holonomic constraints. Thus the principle of d'Alembert and the minimal action principle involving the multiplication rule are not compatible in the case of systems with non-holonomic constraints. For simplicity the proof is given for autonomous systems only, with one general non-holonomic constraint, which is linear in the generalized velocities of the system. 
Christofer Cronstrom and Tommi Raita