We have already discussed that in an open belt drive, both the pulleys rotate in the same direction as shown in Fig.
Let
r1and r2= Radii of the larger and smaller pulleys,
x = Distance between the centres of two pulleys (i.e. O1 O2), and L = Total length of the belt.
Let the belt leaves the larger pulley at E and G and the smaller pulley at F and H as shown in Fig. Through O2, draw O2 M parallel to FE.
From the geometry of the figure, we find that O2 M will be perpendicular to O1 E. Let the angle MO2 O1 = α radians.
We know that the length of the belt,
L = Arc GJE + EF + Arc FKH + HG
= 2 (Arc JE + EF + Arc FK)
