54 Description of motors  Let’s call the 3 motor configurations T, G and H to depict the three different motor types. Within each  configuration there were minor design changes for various applications. Every motor was to be redundant.  T – This motor configuration was a traditional design with the rotor on the inside and the stator on the  outside. The design required a 0.75 slot per pole configuration, i.e. being an 18-slot, 24-pole, 3-phase, redundant machine. This configuration was necessary to meet a requirement that the phases were to be separated by 120 degrees mechanical and the primary and redundant phases to be separated by  60 degrees mechanical. The stator O.D. was given as 9.1427 to 9.1440 cm (3.5995 to 3.6000 inches) and the rotor I.D was 4.8 cm (1.9 inches). Two different stack lengths were required for two designs within this configuration. The motors were to be sinusoidally commutated using resolver and drive electronics which were not part of the task at hand.    G - This configuration was an “inside-out” design, the rotor was on the outside and the stator was on the  inside. The configuration for all 3 variations of the G motor design was as above, 24 pole, 18 slot,  3 phase, and redundant. The rotor specified O.D. was 12.6 cm (4.98 inches) and the stator I.D., which mounted to the program’s equipment, was given as 6.6040 to 6.6053 cm (2.6000 to 2.6005 inches). The different variations for this configuration were, again, in the stack length and motor performance parameters.   H – These motors were also of an “inside-out” configuration with the same slot design as in the G motor.  The primary difference was size and performance parameters. The required rotor O.D. was 15.51 cm (6.105 in) and the specified stator I.D. was between 11.430 to 11.431 cm (4.5000 to 4.5005 inches).  Initial Major Design Restrictions and Design Concerns  Restrictions:  The restrictions listed below are not necessarily required by a designer to comply with the  performance parameters, and were partly responsible for some of the difficulties encountered during the design process. It was assed that these restrictions were a mandatory requirement of the customer for achieving an “identical" motor.  1 - Magnet material must be Samarium Cobalt  2 - Lamination material must be Carpenter 49 (High Nickel Steel)  3 - Primary and Redundant windings must be spaced at 120 degree intervals for each of the three phases  alternating every 60 degree increment  4 - Stators were not to have a skew  5 - 0.75 slot per pole configuration with 18 slots and 24 poles was required.  Had these restrictions not been applied, several design techniques, such as 2.25 slot per pole design   (24 poles 54 slots) without the angular separations, which were a more standard configuration for us, might have been used. Another familiar configuration, like a 72 slot (3 slots/pole) with a skew, might have also been employed. Given some degree of dimensional freedom, the Aeroflex zero-cog approach might also have been used thereby guaranteeing a low distortion sinusoidal BEMF waveform with very low drag and detent results. In other words, allowing a manufacturer to use more familiar designs, techniques, and materials while meeting the specific performance and environmental conditions can often lessen problem areas encountered than with the requirement to match exactly the mechanical and material design details as manufactured by another company.