## 3 Design and Implementation
### Design  
This section highlights the design process, files, and features. The mechanical design of the RSC helped bring to life the required features, particularly those relating to verbal and non-verbal social interaction (Table 3). Given the compactness and multimodal-interaction requirements (Req 1), the main challenge was packing several components into a confined space, keeping them protected, and enabling tool-free maintenance access. The RSC (Figure 2) adopts an hourglass-like shape, which sits comfortably in the hand (Req 2). We employed snap-fit assembly to house the internals with the construction parts (Tables 4 and 5). The top lid (white) features an arcade button and snaps into place (Figure 3), locking the front and back panels. The front panel, featuring a small screw-mounted touch display, slides into place with the help of guide grooves embedded in the main body (blue, Pi bracket). Similarly, the rear panel, with openings for power-supply connectors, also slides into place using these grooves. On either side of the main (blue) body are two small, flat, conical servo-mounted flippers (white). The servos rotating the flippers are press-fit into \begin{table}
\begin{tabular}{c c c} \hline \hline
**Construction Part** & **File Name** & **File Format** \\ \hline Rear panel & back\_panel & STEP, 3 MF, F3Z \\ Flipper & rsc\_flipper & STEP, 3 MF, F3Z \\ Front panel & LCD\_panel & STEP, 3 MF, F3Z \\ Lid & button\_neopx\_panel & STEP, 3 MF, F3Z \\ Pi bracket & Pi\_bracket\_panel & STEP, 3 MF, F3Z \\ Speaker base & speaker\_base & STEP, 3 MF, F3Z \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Design-file summary; more information in the project’s GitHub repository [36]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Interaction** & **Description** \\ \hline Speech & Employing a speaker and microphones to recognise and respond to audio queries. The RSC uses Speech-to-Text (STT) software to capture user speech and Text-to-Speech (TTS), with a language model generating responses. \\ \hline Gesture & The RSC can communicate using gestures by rotating the flippers, expressing responsiveness. This indicates the RSC is ready to engage; for example, it may greet the student with a waving gesture. \\ \hline Tactile & The top-mounted arcade button provides a direct touch interaction. Pressing it can, for example, start a conversation, which may foster a sense of privacy. \\ \hline Touchscreen & The RSC includes a touch display for adjusting settings and showing information. \\ \hline Light & An RBC LED ring maps colours to device states such as loading, conversing, or an error state. \\ \hline Sound & Audio cues convey internal device states by providing an audible speaker and microphone test. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overview of social-interaction modalities. the main body. At the base of the RSC is a screw-attached bell shape (blue speaker base) hiding an embedded bottom-firing speaker and ending with a round anti-slip padding detail (white). Figure 3: Exploded assembly view of the RSC. Components are denoted by yellow highlights and blue arrows, while 3D-printed construction parts are indicated by orange highlights and red arrows. More information on the assembly can be found on the project’s GitHub page [36].