I would suggest a general Lagrange dynamics approach, with generalized coordinates and forces. In the simplest model, assume rigid links of the pendulum, lumped masses and rotational inertia. A spherical joint has two angular degrees of freedom: zenith angle and azimuth. Derive the potential and kinetic energy of the entire system vs. the generalized coordinates and their derivatives, respectively. Then apply Lagrange method, and you will get a set of ordinary differential equations of motion. Good luck