Power Distribution

Power

The power source for kupe will be one or two 12v batteries. Currently I am using one 12V 7Ah lead-acid battery. I have enough room to replace this with a 14Ah device or use two 12V 7Ah batteries instead. These could be connected in parallel or series if I decide to move to 24v drive and change the motors.

I will stick to lead-acid batteries for now as they add extra weight (traction), are easy to charge and are a safe technology. There are drop-in lithium replacements but I see no need to go there at this stage.

Power from the batteries goes through a simple power board (a set of connector blocks and an on-off switch) and feeds the motors via the Motor Driver Board. It also powers the 3v/5v Power distribution board.

Power Distribution Board

Moana had plentiful 5v and 3.3v power distribution, including a USB socket. This worked well and kupe will use a similar mechanism. I pulled the buck converters from moana and reused them on a veroboard power distribution board. There is provision for ten 5v taps and ten 3.3v taps. The buck converters used were Pololu 5V, 5A Step-Down Voltage Regulator D24V50F5 as well as a Pololu 3.3v 2.5A regulator.

Powering the Raspberry Pi

The Raspberry Pi 5 I will add for optical processing needs power from a USB-C connector. I have a USB-A socket on Moana which I could repurpose (and connect via a USB-A to USB-C cable). I'm near the limit of what a USB-A can source with a Pi5, and if it proves troublecome, I will replace it for a USB-C daughter-board.

The usb daughter board was mounted on the extrusion above the power distribution board. During tests, it was found that there is insufficient voltage to power the Pi reliably. It works but gives warnings and runs slowly. I'm unsure whether this is the connector/cable or the power distribution mechanism. I may need to use a custom power board for the Pi5 as it can draw considerable current. Given that the Pi5 can potentially draw much more current than the Pi3 used on Moana, I suspect I need a dedicated supply, espwcially if the motors are drawing significant current.

TODO Investigate different connectors and cables. If still an issue, use a separte power drive for the Pi.

May 2026