Abstract: A downhole drilling motor includes a rotor and stator of the Moineau positive displacement type within a housing. A drive shaft is rotatably mounted within the housing. A flexible shaft with a polygonal connection at each end transmits the rotational motion of the rotor to the drive shaft while compensating for the eccentric movement of said rotor within said stator relative to said drive shaft.

Abstract: A downhole motor includes a bearing assembly for allowing rotational and bidirectional axial movement of a drive shaft in a housing. The bearing assembly includes a stationary race member, a displaceable race member, ball bearings disposed between the race members, and resilient load carrying members for distributing axial thrust loading from the drive shaft to the displaceable race member when the drive shaft is axially displaced in a first direction. The bearing assembly further includes resilient preload members for maintaining the ball bearings in contact with the race members in the absence of axial loading and when the drive shaft is axially displaced in a second direction. The downhole motor of the present invention provides a high axial thrust load capacity, prevents shock loading on the bearing assembly during sudden changes in the direction of axial loading on the bearing assembly and exhibits improved durability during cyclic bidirectional axial thrust loading.