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Good idea on the Custom Connector Board! I think the Conn Bd should be attached to the PCB Mill bulkhead, then connected down to the Blue Box on a single cable. This will allow us to run cable track spines across the Axis, and connect nearby. The spines tend to make wires last much longer by minimizing metal fatigue in wires.
The Optos only require 3 pins; power, ground, signal. The motors require 4 (or 6 for better 2 phase motors). If we use a locally mounted Conn Bd, we already have long enough leads.