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(c) Flat belt Drives

a = angle of wrap of smaller pulley, radians (1 rad. = 57.3 deg.)
m = coefficient of friction between pulley and belt
R₁ = radius of smaller pulley,in.
R₂ = radius of larger pulley, in.
c = center distance (O₁O₂), in.
f = sin^-1 (R₂ - R₁) ; Oº <= f <= 90º
                    C
H.P. = horsepower transmitted by belt
N_D = RPM of driving pulley
R_D = radius of driving pulley (i.e. either R₁ or R₂, dependinding on which is the driver)

The maximum bearing load on either pulley shaft occurs when the belt is transmitting the maximum horsepower (i.e. the belt would slip if the horsepower were Increased above this level). Under this condition the maximum bearing load is given by:

Max. bearing load = (63,025)H.P.   ( e^µa+1   )  cosØ lbs.                                                                         (5)
                                  N_DR_D           e^µa-1

Note: In the case of chain drives the bearing load is often approximated by the pull on the tight
        side of the chain, the slack side being assumed tensionless.

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