This article develops and evaluates state-dependent parameter~(SDP) control systems for the hydraulically actuated dual-manipulators of a mobile nuclear decommissioning robot. A unified framework for calibration, data collection and SDP model identification is proposed, in which the state-dependent variable is a delayed voltage signal associated with the time-varying gain of the system. The latter can cause undesirable joint movements when the device is regulated using linear control algorithms. By contrast, the present article develops a novel nonlinear pole assignment algorithm based on the SDP model. Closed-loop experimental data shows that the SDP design more closely follows the joint angle commands than the equivalent linear algorithm, offering improved resolved motion.