The endless belt of an escalator passes around idler drum A and is driven by a torque M applied to drum B. Belt tension is adjusted by a turn- buckle at C, which produces an initial tension of 1000 lb in each side of the belt when the escalator is unloaded. For the design of this system calculate the minimum coefficient of friction µ, between drum B and the belt to prevent slipping if the escalator handles 30 people uniformly distributed along the belt and averaging 150 lb each. (Note: It can be shown that the increase in belt tension on the upper side of drum B and the decrease in belt tension at the lower drum A are each equal to half the component of the combined passenger weight along the incline.) couple M required to turn the pipe in the V-block against the action of the flexible band. A force P = 25 lb is applied to the lever, which is pivoted about O.

The coefficient of friction between the band and the pipe is 0.30, and that between the pipe and the block is 0.40. The weights of the parts are negligible.