Hidden and self-excited attractors in electromechanical systems with and   without equilibria
  This paper studies hidden oscillations appearing in electromechanical systems with and without equilibria. Three different systems with such effects are considered: translational oscillator-rotational actuator, drilling system actuated by a DC-motor and drilling system actuated by induction motor. We demonstrate that all three systems experience hidden oscillations in sense of mathematical definition. But from physical point of view in certain cases it is quite easy to localize there oscillations. 
M.A. Kiseleva, N.V. Kuznetsov, G.A. Leonov
math.DS nlin.CD