Tendon-based Stewart platforms are capable of high speeds and accelerations. Thus, a reliable controller running with a high frequency is required. Here, an implementation based on a modular controller architecture is shown. To control the platform on a given trajectory, the implemented position control has to be extended by a tendon force control which generates defined and safe force values. In the case of one redundant tendon, a direct calculation is possible. Having at least two redundant tendons, the computation of a force distribution requires optimization methods, which are numerically expensive. In this paper, algorithms for both cases and their embedding into the controller are presented.