Motor

A motor having a housing, a rotor rotatable relative to said housing, and a radial ball bearing disposed between said housing and said rotor, wherein

• a plurality of rolling balls are confined between an inner ring and an outer ring of said ball bearing and arranged circumferentially with substantially equal intervals therebetween, said inner or outer ring of said ball bearing having a rolling-ball race whose radius renders said rolling-ball race substantially F-piece symmetrical with respect to rotation, said rolling-ball race having certain undulations in which a pressing region where said rolling balls are pressed between said inner ring and said outer ring and a non-pressing region where said rolling balls are released from the pressing are repeated at a substantially constant central angle,
• said undulations satisfying the following relationship with a load applied to said rolling balls:
• K(Q.sub.max.sup.2/3 +Q.sub.min.sup.2/3)=.alpha.A
• where:
• K:
• constant of proportion
• A:
• amplitude of undulations
• Q.sub.max :
• the maximum value of Q.sub.sum (.theta..sub.0)
• Q.sub.min :
• the minimum value of Q.sub.sum (.theta..sub.0)
• .ltoreq..alpha.<
• 1
• (Q.sub.sum (.theta..sub.0) representing the sum of
• Q.sub.n (.theta..sub.0)=K.sup.-1.5 {-4sin F(.theta..sub.0 -.phi..sub.n }.sup.1.5 .multidot.cos (.theta..sub.0 -.phi..sub.n)
• where:
• .theta..sub.0 :
• angle of rotation of said rotor from a fixed position
• .phi..sub.n :
• the angular position of a rolling ball with respect to a certain reference position
• F:
• the number of the cycles of undulations).