Why are you doing the 9 volt at all? Do you have something that can only use 9? I would just have a 6 volt battery run everything unless you need 12v for more power to drive motors. In that case use a 12v battery and a 6 volt BEC for the servos. Electrically varied + positive voltages can share a common - ground but you also want to keep your system as simple as possible.

Thanks. There are a couple things that need 12 volts in my setup, a couple that need USB power, some lights that work best at 9V, different power demands of the 2 types of servos-- an unfortunate mix, which the power distribution board helps with.

It sounds like the one ground will work, if I'm interpreting things correctly.

Frank

One ground will. What I suggest is having one power source. 12v then to get 6v use a 6v bec for the your servos and you can use a buck step down adjustable converter to get your regulated 9 volts. Its cheap... Easy and only one battery. Both the BEC and step down converter are found for a few dollars on eBay - Josh S

Thanks, Josh!

Frank