The Challenge
Context: A smart bike is only smart if it can talk to the cloud. The “Sonoma” module was the brain of the Watson e-bike.
The challenge was packaging a cellular modem, GPS, Bluetooth, and main compute board into a compact, bomb-proof enclosure that sat on the rear fender.
- RF Performance: The enclosure had to be RF transparent for LTE/GPS but structurally rigid enough to handle impact.
- Thermal: The cellular radio generated significant heat, but the unit was sealed (IP67) and sat in direct sunlight.
- Interconnect: It had to blind-mate to the bike’s harnessing during a “hot swap” battery change.
Engineering Approach
We designed a sealed “Black Box” (or rather, a white one) using weather-resistant PC/ABS.
- RF Window: We utilized a specific plastic grade that minimized signal attenuation, simulating antenna patterns to ensure connectivity in urban canyons.
- Thermal Management: I integrated a conductive thermal pad strategy to dump heat from the modem shield into the mounting bracket, turning the bike frame itself into a heatsink.
- Gasket Design: We used a custom perimeter gasket compressed by 6 custom security screws to ensure a 5-year watertight seal against pressure washing.
Impact
This module enabled the “Dockless” capability of the fleet.
- Connectivity: Maintained reliable LTE link even in dense urban environments.
- Survival: Zero water ingress failures reported in pilot deployment.
Project Artifacts
:::note[Specs]
- Comms: LTE / GPS / BLE
- Enclosure: PC/ABS UV Stabilized
- Seal: Custom Silicone Gasket :::