P yA M SB cos a M o x 2,研究轮 Xo=-Ptana Yo=-P M-PR ∑M(F)=0 S4cosaR-M=0 ∑F=0 Xo+Ssina=0 ∑F=0 Scosa+Yo=0SA cosR−M =0 XO +SA sin=0 SA cos+YO =0 XO = −P tan YO =−P M = PR 2，研究轮 Fx = 0 Mo (F) = 0  Fy = 0 cos P SB =