In a certain problem regarding motion of a particle in a gravitational field with axial symmetry, I have an expression of an effective potential $\Phi_{eff}(r,\theta)$. Now, I am interested to study the motion of the particle in the $r-\theta$ plane. Spherical coordinates $(r,\theta,\phi)$ is used in the problem and the axial symmetry corresponds to the $\phi$ coordinate.
How to obtain the equations of motion from $\Phi_{eff}(r,\theta)$ that I can numerically integrate to obtain the trajectory of the particle?