An unexpected power system
The driver board turned out to carry a complete power system: a 3S charge circuit, a regulated 5 V rail, INA219 current and voltage monitoring, and an external DC input feeding all of it. We had been designing a custom distribution board to do exactly those four things. That board is now cancelled. This is the second time on this platform that reading the hardware carefully has been worth more than a week of design work.
What we learned
- We were building a subsystem that already existed, three metres away, unopened. Inspection is cheaper than design and we did it in the wrong order.
- Integrated current monitoring is worth more than the board we were designing, because it gives power telemetry for free from day one.
- The trade for cancelling the board is real: we now depend on charge behaviour we did not design and cannot see the source of, which is why verification became an open challenge rather than an assumption.
Next steps
- Cancel the custom distribution board and archive the design.
- Verify charge termination and rail behaviour with an external meter before trusting the onboard telemetry.
- Read the driver board documentation end to end before adding anything else to the platform.
Hardware referenced
- Waveshare onboard power systemWaveshareIntegrated 3S charging, regulated 5 V rail, INA219 monitoring
- External DC charging inputWaveshareDC barrel jack to onboard charger
- WAVE ROVER 4WDWaveshare4WD skid-steer base, integrated ESP32 driver board
Open challenges touched
Charging verification
The onboard charger appears to bring the 3S pack up correctly, but termination voltage, termination behaviour, and cell balance at the top of charge have not been confirmed with an external meter. Until they are, charging stays supervised and the platform does not sit on the charger unattended.
Decisions referenced
Use the onboard Waveshare power system rather than a custom distribution board
The custom power distribution board planned for the platform was dropped once the rover's integrated charge, regulation, and current-monitoring circuitry was identified during inspection.
- The integrated system already provides 3S charging, a regulated 5 V rail, and current monitoring — the three things the custom board was being designed to do.
- A board we do not have to design is a board we do not have to debug, and the schedule saved goes into the control link.
- Using the stock path keeps the platform serviceable by anyone with the vendor documentation.
- Build the planned custom distribution board — Rejected — duplicated existing hardware for no capability we could name.
- Bypass the onboard system with an external charger — Rejected — would mean opening the chassis for every charge cycle.
Outcome Removed an entire electrical subsystem from the plan. The trade is that we now depend on behaviour we did not design, which is why charge verification is an open challenge.
Images
Charge circuit, regulator, and current monitor identified on the stock board.