The problem of determining the inclination angle of a pendulum on a cylinder

The problem of determining the phase coordinates of a pendulum on a cylinder by measurements of the inclination angle of the cylinder relative to the pendulum is formulated and solved. A necessary and sufficient condition for observability is found. A linear Luenberger observer is constructed whose output variables are used to close a linear feedback control system. Numerical experiments are performed showing the possibility of using this type of control (by means of variables of the observer) in a nonlinear model of controlled motion of a pendulum on a cylinder.