Fig. 38. Trolley Base.
Trolley Base. The trolley base upon which the trolley pole swivels, and which furnishes the tension that holds the trolley wheel against the wire, is designed to maintain, by means of springs, an approximately even tension against the trolley wire, whether the trolley wire is high above the track or near the car roof. This is done by changing the relative leverage which the springs of the trolley base have on the trolley pole according to the height of the trolley pole.
Fig. 39. Trolley Wheel.
Fig. 38 shows one form of trolley base. The trolley base is bolted to a platform constructed for it on the roof of the car; and the supply wire to the motors and other electrical devices on the car, except in cases where a wooden trolley pole is used for certain special reasons, is connected directly to the trolley base. An insulated trolley wire is run down the wooden trolley pole, and connected through a flexible lead to the car wiring.
Trolley Poles. The trolley poles in general use are of tubular steel, which gives the greatest strength for a given weight, and which can usually be straightened if the pole has been bent by striking overhead work when the trolley wheel leaves the wire.
Trolley Wheels. Trolley wheels are from four to six inches in diameter over all, the small wheels being used in the city service, and the large wheels in high speed interurban service. A typical trolley wheel is shown in [Fig. 39]. Various companies use various forms of groove in the trolley wheels, some adopting a groove approximately V-shaped. The U-shaped groove, however, is the most common. The trolley wheel is made of a brass composition selected for its toughness and wearing qualities.
Fig. 40. Trolley Harp.