Automatic Motor Base for Nema Frame 284, 286. The Automatic Motor Base maintains proper belt tension when experiencing speed change due to work load and belt wear. The base can adjust belt tension while in a dynamic condition. Spring controlled tension eases the operating stress and dramatically extends the life of belts and bearings. The automatic motor base also increases energy efficiency by maintaining optimal belt tension for peak performance. Belts can be changed without loosening alignment and without having to loosen the motor mounting bolts, reducing the time and expense invested in routine maintenance.