Depending upon how the supply is configured or the distance between the supplies and the driver boards, the S + may have to be connected to the Out + either right at the supply or at the driver board and the S – may have to be connected directly to the Out – either right at the supply or at the driver board.
The ground connection between the Out – and Out + and the ground connection between the two servo drivers should be a very heavy gauge low resistance wire.
The power supply ground connection is optional and is usually not connected.
