This partial class contains common connectors needed for wheel models.
In particular, frame_a is intended to connected a wheel
carrier (also called upright) and flange_a to connect
a driveline.
This class should be extended to create
a proper model, see e.g.
IdealWheelJoint model.
Note: the loss power has to be provided by an equation in the model which inherits from this partial model, such as
WheelInterfaces model(lossPower = ...).