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Experimental Trolleybuses for London
Page 119
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TN order to ascertain the most suit'able type of trolleybus to operate over the routes which it is proposed, in the near future, to convert from tramway working, the London Passenger Transport Board recently _ placed in service two experimental vehicles. These are now running on the Wimbledon-Hampton Court route. One has as its basis a standard A.E.C. 663T six-wheeled chassis, with the wheelbase increased to 18 ft. 7 ins., making the overall length of the vehicle, 29 ft. 11 ins. In the other a standard A.E.C. 661T chassis is employed, this having a sVheelbase of 16 ft. 3 ins, and giving an overall length of 25 ft. 11 ins. • The six-wheeler has a M.C.W. 73-seater body and MetroVickers' electrical equipment, whilst the four-wheeled 60-seater has an English Electric body and electrical equipment by the same concern.
With the main exceptions of brake gear—a G. D. Peters' compressor on the larger model and a Westinghouse compressor on the smaller—the general equipment on the two vehicles is almost identical. Both units are driven by self-ventilated compound motors, provided with special winding to give improved motor characteristics with regenerative control.
On the 73-seater a MetropolitanVickers' scissors-type controller is used, whilst on the 60-seater an Eng lish Electric drum-typet controller is employed. In each case the controller is arranged to energize and de-energize the main and shunt contactor coils in correct sequence for acceleration when the pedal is depressed, and for retardation by regeneration on the first part of its return. 'Further retardation is effected by rheostatic braking on the later part of the return stroke; a compressed air brake is also fitted.
The special motor characteristics ensure automatic electric braking, with an even deceleration of not more than 4.5 ft. per sec. per sec. irrespective of the manner in which the control is operated by the driver. Automatic regeneration is provided down to Speeds of 10-12 m.p.h., followed by smooth rheostatic braking at speeds below this figure.
• Two safety measures are worth noting. In the first place all electrical units are mounted directly on the
chassis and are provided with secondary insulation. Secondly, an automatic 'buzzer is mounted in the driver's cab to give instant warning should the brake pressure fall below a sale figure.
A motor generator set of new design is incorporated for providing low
voltage lighting. And radio-interference suppression coils are connected in the trolley circuit.
In the case of the larger vehicle, the Isd.C.W. body is of all-metal construction, has a rear entrance and includes emergency exits on both decks—that on the lower being achieved by setting back the rear panel. Seats are of the lightweight pattern with Dunlopillo cushions and moquette coverings.
An all-metal body is also employed for the four-wheeler. A similar vestibule type entrance is included and a rear window in the upper saloon is also designed for emergency purposes.