Keeping the Fans Dry

This article focuses on controlling of a 13,000-ton retractable steel sodium roof of the Safeco field. The roof is built in three telescoping sections, which spans 8.9 acres, travels atop two parallel elevated runways along the length of the stadium’s north and south sides. The basic intent behind Safeco Field was to honor the open-air tradition of vintage ballparks, such as Boston’s Fenway Park and Chicago’s Wrigley Field, while protecting players and fans from the fickle Northwest weather. When needed, the roof will move out over the field at a speed of 30 feet per minute, with the leading end section traveling the longest distance, 532 feet. This giant umbrella relies on a network of 96 adjustable-voltage dc motors driving 36-inch-diameter wheels along steel rails, all load balanced with the help of “cutout” gear couplings, specially modified for quick, easy deployment.