I can understand that in the hydraulic case rotating seals are required between the stationary and moving parts, but I still don't understand why hydraulic "slip rings" are required in a hydraulic motor. In this case the core is stationary, whilst the outer casing is what's moving. Hence my confusion as to why "slip rings" would be required to connect to a stationary assembly - the motor core in this case. If you have a diagram of some sort that demonstrates why hydraulic slip rings are required in this configuration, it would help a great deal at this point.

In a ceiling-fan motor, what would be the stator in a conventional induction motor takes the place of the rotor and vice versa. The roles are reversed. The power is fed to the stator, of course, but in this case it is physically the motor core that is stationary, contains the field windings, and functions as the stator - not an annular ring around it as would be the configuration in an ordinary motor. The motor is, in effect, turned "inside out." Power is fed, without the need for slip rings, to the core whilst the case is free to rotate. All of the ceiling fans in my house are built this way.

-e