Most of the time, when you will assemble a Robotis Dynamixel with a Poppy part, you will have 2 orientation options. To be compatible with our convention and configuration, you should keep the same orientation as us when you will assemble your Poppy.
This picture is not really clear, but the red arrows indicate the orientation of the motor i.e. where should be oriented the driving horn (HN07/05-N101):
