you need to connect all grounds to a same point

That's slightly misleading. You need to tie all grounds together, you don't necessarily need to connect them at the same point.

What I did was cut in to the supply to the EZB, fitted a 6V regulator, made up a board for +6V and Ground. Then had the white to the EZB and the red & black to the 6V board.

Thanks.

If I connect 2 ground wires together (in a Y shape), and send one end to the servo, one end to the external 6V power supply and one end to the EZ-b, will that do the trick?

Frank

Is the External 6V power also supplying the EZB? If it is you needn't send it back there.

I think you can just link the grounds of all supplies together, so a short jumper from batter 1 ground to battery 2 ground (await confirmation, I'm not completely sure on that).

@Kudo its called common ground . if ezb and servos are powered by the same 6v source they have common ground and a separate ground wire is not needed. You would only need a ground wire if the power source feeding ezb was separate from the power source for a motor/servo which is called uncommon ground and a separate ground wire connection would be needed.

@Josh, can you just connect the 2 grounds of the batteries together? Really unsure on that one as I've not had to do it.

Yes you could connect the grounds together. It just cannot feed pos from ezb.... It needs to be direct to power source because ezb regulators have limitations.

My setup would be a 12V battery going to a power distribution board. 9V from that board goes to the EZ-b and 6V from that board to the servo. So indirectly, the same battery is powering both the EZ-b and servo. In this case, is one ground going to the 6V part of the power distribution board sufficient?

thanks again,

Frank

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