This is my first reply under the new software, here goes…
First, I have to say this is fine White Paper, well done guys.
Second, I have to point out that copper clad aluminum wire is illegal for use on FRC robots under R60.
Yes SB120 connectors are legal, but as Allan pointed out above and as specified in the Robot Rules, many batteries and in particular those provided in the Spare Parts will be wired with the SB50.
As to wire sizing, each 3 steps in AWG wire size is approx. doubling or halving the wire conductive cross section. The step from #6 to #4 is less than twice the conductive copper. At 600 amps (the absolute highest current available from a fully charged new battery) would drop .234 volts per foot for the #6 wire and .144 volts per foot for the #4. A typical FRC robot will have about 2 feet of wire length total from battery to PDP, so 4 feet (total for both red and black) would be 0.936 volt for #6 and .576 volts for #4 about 0.4 volts difference when measured at the input of the PDP at max current. Your mileage will vary.
You cannot judge the conductive area by eye. It will vary with strand size. 7 strand wire will have a different diameter than 31 strand wire. Wire purchased on Amazon may not be as advertised as the seller simply measures the cross section and looks up the size on a wire chart. I inspected wire purchased on Amazon as #10 and I measured it at #13. A good hint that the wire is different size is that the wire size is not printed on the wire.
The greatest cause of brownout in my opinion, is slipping battery and wire terminals. I have suggested for many years a method for removing this problem with the addition of a simple #10 external tooth lockwasher. If you place the lockwasher between the battery terminal and the wire terminal, the lockwasher will prevent any movement between the two terminals. No movement results in no loosening of the connection. Please use the locking hardware that comes with most batteries. This would be a split washer and flat washer under the nut. I would estimate over 90% of all brownouts are caused by loose battery terminals. A loose battery connection raises the series resistance of the primary wiring and therefore increases the voltage drop of the primary wiring.