Pancake and PCB
Pancake slip ring assemblies are used where the length along the axis is very restricted. The rings are concentric in a plane, rather than the same diameter along the axis of a cylinder. This leads to design considerations including that the brushes are not moving on the ring at the same tangential speed. Here is a photograph of a Pandect pancake design for the turret of a fighting vehicle.
Some pancake slip rings use a PCB construction. The second picture is of one such Pandect design.