Disclaimer: I am not an EE but I can read schematics and datasheets so please do not consider my statements authoritative.
There are two issues that are addressed:
Downstream Power
The power that exists
- Available budget
The Farmduino Express runs on 24V input with a budget of 150W (6.25A). The 24V feeds to a TPS5430 to power 5V logic and peripherals with a budget of 3A. The Raspberry Pi (RPi) Zero W, included in that budget, has a downstream USB connector with 5V with no regulator or limiting circuitry but it’s generally understood that over 1.2A can be risky. The RPi does have a 3V3 regulator and output. - Power instability
It appears that high consumers on the 24V side of the house can cause significant drops (brownouts) on the 5V side of the house. Unlike the RPi 3B+, the RPi Zero has no power sense circuitry so it cannot report these issues. Additionally, there is a normal power drop over long distances of wire. Any downstream peripherals, including the stock camera (with no regulator), probably want a stable voltage source for measurements and communication. - Noise
The USB camera line, which serves as the only downstream communication line, is unshielded and running parallel to high frequency, high power motor lines over its entire length.
Proposed power
Run a 24V line to a junction box at the Y-Z axis mount point. In the junction box regulate power down to required voltages especially 5V. This works around voltage drop and creates a tap for peripherals.
Downstream Communication
State of affairs
It seems that FB did envision downstream peripherals in its current incarnation. For the wider configurations of FB, running 15ft cables for GPIO pins seems dubious. Not to be down on it, it is a great setup for accessories mounted at the main box. I would like to see a more robust communications design for FB in general.
Proposed downstream comms
Putting aside grand visions, I will settle for USB 2.0. Run a shielded USB extension cable out to an amplifying hub in a junction box at the Y-Z axis mount. Power this hub from the aforementioned regulated 5V in the same junction box.