The flange-mounted gearbox supplies only torque with minimal axial or radial shaft loading. Bearings on the output shaft are only subjected to negligible runout. The input shaft uses a C-Face adapter and flexible coupling, resulting in an alignment-free input connection with no radial or axial loads applied on the input shaft. Operation From 1999 until 2014, the Seattle Mariners played 1,262 regular season games [2] (Figure 6). Even though Seattle has a reputation to be a rainy city, most games were played with the roof open. In this 15-year time period, only 173 games were played with the roof closed, and 104 times the roof was operated during the game. It can be concluded that the roof was deployed for game-related events an average of 18 to 19 times per year. If other reasons are considered (non-game events, field maintenance, roof maintenance, and training), roof deployments may vary from 250 to 400 per year. The intermittent nature of the roof's operation helps prolong the lifespan of the gearbox. However, it's important to note that when the roof is operated in poor weather conditions, it can result in heavy shock loads that put a strain on the gearboxes. To account for this potential overload, the appropriate service factor was carefully chosen.

Maintenance Considering an ambient temperature range of 35 to 76 °F (~2 to 24 °C), it is recommended to use a gear oil with ISO viscosity grade of either 100 or 150 cSt (Figure 7). Mobile SHC 627 oil with viscosity grade of 100 cSt was used in the Sumitomo gearboxes, as this gear oil provides sufficient oil film thickness on hot days and does not affect start-up during cold days.

The following practices are performed during maintenance: ? The oil is checked in all 96 gearboxes every 6 months. ? Every time the roof was deployed, maintenance personnel is located on each runway to check for  abnormal sounds, odors and leaks. ? If any issues were found, these were reported and addressed in a timely manner. Sumitomo recommends changing the oil every 5,000 hours or every 2 years, whichever comes first. T-Mobile Park’s Maintenance Team diligently followed Sumitomo’s recommendation.