costs prompted by the energy crisis, Emerson adapted their "K63" motor, commonly used in household appliances and industrial machinery, to be used in ceiling fans. This new "stack" motor, Along with Encon's cast aluminum 20 pole motor, proved to be powerful, yet energy-efficient, and aided in the comeback of ceiling fans in America, since it was far less expensive to operate than air conditioning. With this design (which consists of a basic stator and rotor), the fan's blades mount to a central hub, known as a flywheel. The flywheel which is made of either metal or reinforced rubber can be mounted either flush with the fan's motor housing (concealed) or prominently below the fan's motor housing (known as a "dropped flywheel"). Many manufacturers used and/or developed their own stack motors, including (but not limited to) Casablanca, Emerson, FASCO, Hunter, and NuTone. Some manufacturers trademarked their personal incarnation of this motor: for example, Emerson's "K63" and later "K55" motors, Fanimation's "FDK-2100", and Casablanca's "XLP-2000" and "XLP-2100". The earliest stack-motor fan was the Emerson, which was an earlier version of the model that was later called "Heat-Fan", a utilitarian fan with a dropped metal flywheel and blades made of fiberglass and later moulded plastic depending on the model. This fan was produced in numerous different forms from 1962 through 2005 and, while targeted at commercial settings, also found great success in residential settings. Casablanca Fan Co. also made stack-motor fans with concealed flywheels rather than dropped flywheels. While this motor is not nearly as widely used as in the 1970s and 1980s, it can still be found in certain high-end Fanimation fans. One disadvantage of this type of fan is that the flywheel, if it is made from rubber, will dry out and crack over time and eventually break; this is usually not dangerous, but it renders the fan inoperable until the flywheel is replaced. Direct-drive ceiling fans employ a motor with a stationary inner core with a shell, made of cast iron, cast aluminum, or stamped steel, that revolves around it (commonly called a "spinner" motor). The blades are attached directly to this shell. Direct-drive motors are the least expensive motors to produce, and on the whole are the most prone to failure and noise generation. While the very first motors of this type (first used in the 1960s) were relatively heavy-duty, the quality of these motors has dropped significantly in