Pendulum with spring loaded sleeve

A rod with mass m_1 swings from a pivot point under influence of gravitation. Along the rod a frictionless sleeve can move, restricted by a spring. The sleeve has mass m_2 and the spring has spring constant k. y1 is the coordinate measuring movement in the direction of the rod. y2 measures the swing angle.
Select initial values for y1 and y1' (position and velocity in the direction of the rod) and y2 and y2' (angular position and angular velocity). Depending on the initial the system can be stable of very chaotic.