This paper presents the development of a model which can adequately simulate the dynamic stability of manipulators mounted on moveable platforms. The model takes into account the dynamics of the base that can potentially rock back-and-forth. Particularly, the model predicts the changes in the velocities of the manipulator links and the base due to impact with the ground. The application of the study is directed at industrial machines that carry human-operated hydraulic manipulators. The model is therefore used to simulate for the first time, planar movements of'a Caterpillar 215B excavator-based log-loader. The results clearly show the effect of the manipulator movement on turning the base over. The results also show that by proper manipulation of the arms, one can achieve a stable condition and even reverse the ‘tipover' situation in such machines.