Equations of motion for a two-axes gimbal system

Equations of motion for the two-axes yaw-pitch gimbal configuration are discussed on the assumption that the gimbals are rigid bodies and have no mass unbalance. The equations are derived and different terms are brought together into separate groups for the sake of clarity and to facilitate certain interpretations. Different kinds of disturbances and their elimination or reduction are discussed, as is the yaw gain dependence on the pitch angle. Inertia cross couplings are also given. The purpose is twofold: to simplify the picture of the two-axes gimbals and to further illustrate the properties of this configuration.