To achieve full holonomic movement, the robot utilizes a **four-wheel Mecanum drive in an X-configuration**. This configuration grants three degrees of freedom ($v_x, v_y, \omega$), allowing the chassis to translate laterally, move longitudinally, and rotate concurrently.

By aligning the wheels symmetrically, the diagonal rollers generate independent force vectors that resolve into holonomic translation. This omnidirectional capability helps the robot perform fine spatial adjustments while tracking line guide curves or navigating through tight environments.

Bridging the 3mm N20 motor D-shaft to the hexagonal hub of the 80mm Mecanum wheels posed a mechanical interfacing challenge. Standard parts did not accommodate the small motor shaft diameter with the larger wheel hub size.

Custom coupling adapters were modeled and 3D printed with 100% infill in PETG to maximize shear and torsional strength. The section view details how the hex-profile key locks directly into the wheel center to prevent rotational slip during acceleration.

Propulsion is driven by four high-torque geared micro N20 motors rated at 6V with a metal spur gearbox (1:30 gear ratio), achieving 300 RPM output speed. They provide sufficient torque for holonomic translation and high rotational speeds.

The encoder feedback is processed via dedicated hardware interrupts to calculate current wheel velocities, enabling closed-loop speed control through PID velocity tuning.

A Raspberry Pi Pico W board coordinates all system actions, utilizing the RP2040 chip's dual-core capability. To handle the high quantity of digital signals needed for motor control, direction, and encoders, an MCP23017 GPIO expander module was integrated.

Communicating over I2C, the MCP23017 manages slow-changing digital outputs (such as motor direction toggles and status lines), saving the Pico W's native GPIO pins for timing-sensitive encoder interrupts.

The firmware splits tasks between the RP2040 chip's two cores. Core 0 manages Wi-Fi SoftAP networking and the WebSocket server, communicating with the Android app.

Core 1 runs a real-time 100Hz control loop handling kinematics, encoders, PID, and safety filters. Cores communicate using thread-safe shared RAM with a snap-shot mechanism, preventing networking delays from blocking the control loop.

A custom-designed Android app, written in Kotlin with Jetpack Compose, acts as the robot control dashboard. The app establishes a WebSocket connection over the robot's local Wi-Fi SoftAP (exposing a server at `192.168.4.1:80`).

The dashboard integrates a multi-tab interface: Control (buttons/joysticks/tilt), Meters (decay timings and speed), Telemetry (proximity radar HUD and speed curves), and Config (limit thresholds and motor speed loop coefficients).

The total project cost was kept within **LKR 29,050**, utilizing standard microcontrollers and modular sensors to manage development budget constraints.

Actuators (the four micro N20 encoder motors and wheels) comprised the largest subsystem cost at **49.9%** of the budget, while control components (Pico W and I2C accessories) were kept to **13.4%**. Power modules (comprising Samsung 18650 batteries, charger circuits, and converters) accounted for **10.7%**, with structural acrylic materials and local fabrication costing the remaining portion.