3.2.2. 3 Motors The following summarizes the motor requirements for the MPTS mechanical system interface: Figure 3.2-4 is a list of typical motor types that are considerations for the servo system design. Control dynamics computations indicate that less than 134 watts power drain is required to drive the antenna in azimuth; however, startup inertia and response to control the effect of base dynamics will require a high starting torque motor. A DC motor is well suited to this application. The long life requirements (30 years) favors the brushless DC torque motor, though these devices are slightly heavier and less efficient than brush motors. Figure 3.2-5 presents a conceptual design for the rotary drive mechanism. The total weight for motors, gears, idler wheels and drive wheels is 12,024 Kg. An attractive option to the motor-gear system would be the use of linear step motors mounted around the periphery of the drive assembly support. These devices have an excellent thrust-to-weight ratio (10:1) and would eliminate the wear problems associated with gears. Figure 3.2-6 is a conceptual layout and weight estimate of a three-phase variable reluctance linear motor system. A significant weight reduction relative to the motor gear approach is indicated. The attractiveness of this approach in terms of reliability, simplicity and low weight strongly suggest that technology efforts be initiated to determine the feasibility of application to the MPTS rotary joint drive mechanism. 3.2.2.4 Power Transfer Devices Figure 3.2-7 summarizes power transfer options and the major considerations in selection. Consideration of all factors leads to a tentative selection of slip rings for the azimuth drive and flex cables for the elevation drive. 3.2.2.5 Slip Rings and Brushes A possible configuration would employ two coin silver slip rings around the mast mounted near the roller tracks for gap tolerance stability. Self-lubricating brushes would
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