I built the HobbyCNC 4AUPC rev.2 four axis board with all components and simply am ignoring the 4th A axis till needed later. I set the 4th axis v-ref to the same value as the other three axis, but I don't think even that is necessary. This board worked first try and pushes my $10.00 Ebay motors along at 80ipm with little heating after hours of use. Happy camper here.
