Colonoscopy is considered the golden standard procedure for the screening of the lower gastro-intestinal (GI) and the prevention of the colorectal cancer (CRC), which nowadays represents the third most common cancer-related cause of death. Recent advancements in robotics, electronics and material science have produced the development of non-invasive devices to access the GI in clinical application, in the form medical indigestible capsule robots, as well as are paving the way for novel robotic system for colonoscopy. Robotic solutions are being proposed by the research community to improve accessibility and image quality for intervention and diagnosis in the GI tract, while reducing the discomfort on the patient. However, very few devices have the potential to successfully navigate the large intestine, due to the complicated structure of the mucosa in parallel with the significant challenge of designing miniaturized robots. Aiming at addressing the limitations of capsule endoscopy and robotic colonoscopy, the design of a novel tethered capsule system is presented in this research work. The robot aims at actively moving inside the colon to prevent the main discomfort factors in clinical settings, while providing a robust and reliable control of the robot position and imaging recording. The system comprises a track-based locomotion strategy that exploits a single motor and a worm gear mechanism to establish full-body track navigation, and the inflation of two toroidal soft chambers to enable the diameter-shifting capability for the system to adapt and match the local lumen of the intestine, thus enabling traction control and optimized field of view of the front cameras. This work presents the first miniaturised and modularised prototype of the SoftSCREEN system, designed to create a sterilisable reusable component and a cheap disposable component. We evaluated this first prototype in a 1:1 scale phantom.