New Trolleybus Built for Lightness
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Special Features in a Fleet of Chassis Recently Built by the Sunbeam Company for Operation in Rangoon
AuCH interest attaches' to the design 1Viof a fleet of 15 trolleybuses recently built by Sunbeam Commercial Vehicles, Ltd., Moorfield Works. Wolverhampton, for the Rangoon Electric Tramway and Supply Co., Ltd. By reason of the operating conditions existing in Rangoon, a chassis of somewhat unusual type was required, lightness being of premier importance.
Among the factors influencing design are the population of this city, which is nearly 376,000, the fact that most of its bus users live a considerable distance from their work, that fares have to be kept low and that the roads, which are mainly well made, carry a big volume of ill-regulated traffic.
High speed, apparently, is a secondary consideration, rapid acceleration and the ability to run smoothly down to a slow-walking pace being of greater importance. All the machines are single-deckers, and they have bodies with neither side windows nor seat upholstery. For its durability and because it is a local product, teak is the wood employed, and the coachwork, like the chassis, is lighter than is customary in this country. Although there is accommodation for 30 pas-' sengers, the floor area is considerably less than would be the case in a bus
for use in this country, because of the smaller stature and lighter build of the natives.
This chassis, which is distinguished by the symbol MF3a, has a wheelbase of 13 ft. I in., whilst the overall length is 24 ft. 31 ins, and the width 6 ft. 91 ins. The front wheels are shod with 34-in. by 7-in, high-pressure tyres and twin 7.50-in.-20-in. low-pressure equipment is used on the rear wheels.
Whilst robust in relation to the load, the chassis frame is lighter than in the normal Sunbeam single-deck design, the side members being 8* ins, deep and having 21-in. flanges.
It is of interest that these machines incorporate the Sunbeam-Lockheed braking system, the drums being 16 ins, in diameter and having shoes 41 ins. wide at the rear and 21 ins. wide at the front.
Electrical equipment made by the British Thomson-Houston Co., Ltd., Rugby, is employed. Here, again, lightness is a characteristic. The motor is a regenerative, compound-wound, 35 h.p. unit, and incorporates a reduction gear affording a ratio of 1.84 to 1. This permits the armature speed to be high, relative to that of the propeller shaft, and enables a 61-to-1 axle ratio to be used.
In this connection it is noteworthy that a maximum road speed exceeding 25 m.p.h, is not required, whilst the arrangement -simplifies the task of ensuring smooth running at 2-3 m.p.h. Cushioning and insulation are both afforded by rubber mountings, ,upon which the motor is supported between two pressed-steel longitudinal members.
Regenerative and rheostatic braking are provided by this power unit, and the master controller, which is of the B.T.H. " scissor" type, is located under the driver's seat, whilst it is operated by an "organ "-type pedal. 13.T.H. silent contactors—smaller than on the higher-powered models—are accessibly accommodated on a panel across the front of the chassis.
To obtain the maximum Cooling effect from the air, the main resistances are mounted on the roof, whilst the shunt resistances are housed under the floor behind the contactors.
There are two single-pole automatic circuit breakers in the driver's compartment, and the electrical equipment also includes lightning arresters, choke coils, a Chamberlain and Hookham differential meter, to indicate the current consumed by the motor, metal-filament lamps for indicating interruptions of the main current • supply and the B.T.H. electric speedometer.
On trials in Wolverhampton, during a 371-mile run with eight five-second stops per mile, the trolleybus consumed, its maker states, 1.8 unitrper mile.
Without collector-gear, the AMU chassis weighs 2 tons 4 cwt. 2 qrs., whereas the normal Sunbeam 32-seater chassis scales 3 tons 6 cwt. The machine represents an important development in trolleybus design, for its lightness enables it to be used in districts hitherto considered unsuitable for the operation of trolleybuses by reason of their size and weight.