Page:Motors and motor-driving (1902).djvu/218

186 cheapest in point of manufacture, though not the most efficient, is shown in fig. 2, where we have, as before, two different-sized wheels, one connected with the motor-shaft and the other with the driving-axle of the road wheels. Instead, however, of their faces or edges being cut into teeth, they are smooth, and the two are connected by a flat leather belt. Here, as before, the wheels will be revolved in relation to each other according to their respective diameters, but, as shown by the arrows, they will both revolve the same way. This is advantageous, for every time the direction of power application is changed some loss takes place. By crossing the belt, however, the pulleys or belt wheels may, if desired, be made to revolve in opposite directions. On the other hand, the



connection, not being positive, but depending upon the tightness or grip of the belt, there is more or less slip, so that the ratio of rotation is not constantly the same, and as, in order to obtain sufficient grip for heavy work, the belt has to be tightly stretched, the two wheels at either end are forcibly pulled towards each other, and some extra friction, through pressure, produced in the bearings. The slip of the belt, however, is not altogether a disadvantage, as it absorbs the shock of the engine and prevents damage from that cause, whilst there being no metallic parts in contact, belt driving is quite silent in running, and this cannot be said of gearing, much of which is very noisy, which is not only an annoyance but an eventual source of trouble, as noise means wear.