This study investigates a modified electromechanical actuator for a guided ammunition fin control system. This modification, which is required due to space limitations, is the use of an eccentric type inverted slider crank mechanism instead of a centric type inverted slider crank mechanism. Brushless DC motor-driven mechanism is modeled experimentally. Using the obtained model, the H∞ type robust position controller is synthesized in the simulation environment and applied to the real system in hardware in the loop tests. The effectiveness of the proposed mechanism and the performance of the synthesized robust position controller are verified by comparing the pre-determined performance requirements and the obtained tests results. It has been shown that for a constant volume, the eccentric type mechanism provides about a 7.6% reduction ratio advantage over the centric type mechanism.