After nearly 200 km with the initial version, the time has come for a redesign.
The main control unit is now housed in a 3D-printed case.
The Raspberry Pi Zero has been swapped for an Arduino RP2040 Connect. Same MCU, but can be powered directly from higher voltage (9 V at the moment, but a 2S Li-Po would work as well), and comes with some very interesting on-board peripherals. To facilitate experimentation and iteration, the internal electronics are mounted on a proto-board which has a grid of copper pads on the back side.

The OLED display is no longer inseparable from the wiring harness; it can now be disconnected to take everything apart more easily.

The wiring harness fans out into 3 branches: rear light, wheel speed sensor, OLED display.

It is clear from the picture that the new housing is rather oversized. This is not a mistake, but rather a "conservative approach". In the next phase of the project, I would like to design a custom PCB for the control unit, and shrink the enclosure accordingly.