Progress in minimally invasive surgery increasingly demands tools capable of precise, dextrous manipulation, motivating the development of miniaturised, steerable systems. Such systems have been explored in the past, yet most have shortcomings in their controllability. This thesis presents the design and realisation of a mechanical control unit for a cyclically substitutable, parallel-segmented surgical tool intended for minimally invasive procedures. The developed device, named the Cyclical Snake Controller (CYSCO), introduces a single intuitive slider to drive segment substitution and cartridge shifting. The design emphasises simplicity, compactness, and reliability by incorporating only a few moving parts, with the slider-block and stairbeam mechanisms enabling continuous cycling of tip segments. A prototype was constructed featuring a 10 cm snake-like tip comprising five active segments and five stored segments. Performance testing demonstrated that the prototype completed predefined curved paths in mean times of 48 seconds for a C-curve and 45 seconds for an S-curve. Targeting accuracy showed absolute maximum mean errors of 0.5 mm for the C-curve and 1.6 mm for the S-curve, while the maximum footprints were measured at 31.65 mm and 33.27 mm respectively, validating the feasibility of the concept. This study is a strong demonstration that intuitive, mechanically actuated segment cycling is feasible and provides a solid foundation for further development.