A bearing assembly for a strain wave drive includes a full complement of bearing components arranged to be mounted closely adjacent each other around the peripheral extent of a wave generator. The number of bearing components is the maximum number of said bearing components that can be accommodated in the peripheral extent. The assembly can be includes in a strain wave drive that includes a wave generator arranged to rotate about an axis and having an elliptical cross-section and a flex spline mounted around the wave generator. The bearing assembly can be located around the wave generator between the wave generator and the flex spline.

A method of designing a ball bearing includes providing a value of a shaft outside diameter and a load. An inside diameter of a bearing inner ring is determined based on the value of the shaft outside diameter. A ball size having a specific ball diameter is selected and a number of the balls of the selected standard ball size required to support the load is determined. A pitch diameter of a pitch circle of the ball bearing is determined based on the determined number of balls of the selected ball size. A suitability factor is calculated for the particular value of the pitch diameter and the particular pitch diameter is validated as suitable when the suitability factor is between calculated upper and lower limits.

A spherical roller bearing for a wind turbine main shaft includes an outer ring, an inner ring having a bore with a diameter of at least 499 mm, two sets of spherical rollers which roll on raceways of the rings, and at least one roller cage. Each cage includes an axial inner cage ring extending in a circumferential direction of the bearing, a first axial outer cage ring spaced from the axial inner cage ring on a first axial side and connected by cage bars to form pockets receiving the first set of rollers, and a second axial outer cage ring spaced from the axial inner cage ring on a second axial side and connected by cage bars to form pockets receiving the second set of rollers. The cage bars are at least partially arranged at a position in a radial direction that is offset to a pitch diameter.