The Driven Pendulum at Arbitrary Drive Angle
  We discuss the equation of motion of the driven pendulum and generalize it to arbitrary driving angle. The pendulum will oscillate about a stable angle other than straight down if the drive amplitude and frequency are large enough for a given drive angle. The emphasis is on the parameters associated with a simply made demonstration apparatus. 
Gordon J. VanDalen (Embry-Riddle Aeronautical University)