Automation of excavation operations can be realized by an automatically controlled excavator system that is able to perform autonomously a planned digging work and to quickly comply to interacting forces experienced during excavation. The development of such an automated control system is usually based on a dynamic model of the system that describes the motion with time. A dynamic model for an excavator that is needed for the controller design can be derived by applying Newton-Euler equations to each link in succession. The model obtained describes the motion of the excavator. It corrects several shortcomings that appear in previously published excavator model. On the basis of the model derived, a proportional-differential controller is designed that makes the bucket to track a specified trajectory. It can be used to automate the machine operations, for example, for terrestrial and planetary excavations as well as for mining applications.