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A GUY SIX-WHEELED TROLLEY-BUS TESTED

9th December 1932
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Page 40, 9th December 1932 — A GUY SIX-WHEELED TROLLEY-BUS TESTED
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Under Service Conditions

WE have had an opportunity for testing one of the latest Guy double-deck trolley-buses over two recently opened routes in Derby, and planned the trial with a full sense of the essentials of service conditions. Wherever possible the laden test bus was kept in its proper position relative to the usual service which was running at the time our trials were taking 'Place.

Before giving the performance figures obtained, however, it would seem opportune to describe a few essential features of the vehicle. The accommodation is for 56 seated passengers and the vehicle is built to conform with Ministry of Transport regulations in the matter of dimensions. The mean wheelbase dimension is 16 ft. Lli ins., and the front and rear track measurements are 6 ft. 3 ins. end 6 ft. 2 ins. respectively, whilst the road clearance when the bus is loaded is 10 ins.

Power is developed by a compoundwound interpole regenerative motor rated for •75 b.h.p. at 500-550 volts when running at 900 r.p.tn. to 2,500 r.p.m. There are several special features about the motor and its control which will be dealt with later on, but it might be mentioned here that recent development work by the Guy concern has resulted in an improved Rapacity for regeneration of current. This is under the control of the driver until regeneration ceases, when the power pedal automatically trips back to zero .again.

An Adjustable Steering Column.

Steering is effected by an inverted Marks type of reduction gear set in such a manner that the steering column can be raised to different angles to suit various body types. Another feature is that the tubular steering and track rods form oil reservoirs with wick feed to the ball Joints and, in consequence, it is necessary only to replenish with oil after many thousands of miles. This, then, gives a necessarily brief outline of the chassis. The bodywork is by Christopher Dodson (1930), Ltd., London, and there is accommodation for 27 passengers in the lower saloon and 29 on the upper deck. All seats are upholstered in leather and are quite comfortable, whilst safety glass is used throughout, half-drop windows being fitted in each side. As a further aid to ventilation there are side extractor vents in the lower saloon and in the roof of the upper saloon, whilst an intake ventilator is fitted in the bulkhead between the driver's cab and the lower saloon. As one of our illustrations shows, the rear entrance is really very commodious and gives good access to both the stairway and the doorway of the lower saloon.

The interior decoration is well carried out, the ceiling panels being of polished bird's-eye maple, and all mouldings, facia panels, etc., are finished in polished mahogany ; the ceiling of the upper saloon,, is in white enamel. The vehicle is well illuminated from the main current and, in addition, there is an auxiliary lighting set which automatically comes into operation in the event of a trolley leaving the overhead lines.

One of the most interesting features which our tests of all types of vehicle brings to the fore is that of running costs, so, before setting out on a run with the Guy trolley-bus we took a record of the reading of

the meter installed in the driver's cab, this instrument recording the net amount of current taken from the line—a figure which covers the process of regeneration, for the recording apparatus reverses its action with the reversal of the flow of current.

Ti might be mentioned here that as the motor is mounted well forward in the chassis the control connections are short and the general layout of the wiring is cornpart in appearance. An additional advantage of this position of the power plant Is. that it can be mounted relatively high up in relation to the road and it is fairly easy

to provide adequate ventilation for the armature, etc. The power pedal and the reversing lever are, for safety, mechanically interlocked. As the pedal is depressed it first progressively short-circuits the series resistance and then gradually introduces shunt resistance in order to attain the higher road speeds,

lit reverse, however, the interlocking mechanism between the power pedal and the reversing lever prevents the pedal itself being depressed more than about half way, so that the road speed of the vehicle in reverse is kept down to areason

able figure—this was found to be about 12 m.p.h.

A master controller drum is connected to the power pedal (which is operated by the left foot) and gives the driver control of power and regeneration. When coasting a magnetic trip automatically holds the pedal at the position of maximum regeneration, but it can be released, if the driver wishes to coast freely, merely by giving a slight downward pressure on to the pedal; the magnetic trip is automatically freed when regeneration ceases.

Another point worth recording is the fact that provision is made so that if a trolley pole comes off the line and the vehicle comes to a standstill, the circuit for driving cannot be made again until the power pedal is brought back to the first contact.

Ready Response to the Controls.

The action of manceuvring out of the corporation trolley-bus shed on the Nottingham road, demonstrated quickly that the vehicle responded accurately and instantaneously to movements of the control pedal and that the steering and braking mechanisms did not demand much .energy to be expended by the driver. The vehicle could be turned around In the shed between a wall and a pillar set 56 ft. apart.

During our tests the vehicle was

loaded to not quite its full capacity. 2 tons 5 cwt, of ballast and personnel giving about two-thirds load—a figure which might reasonably be expected to represent a fair average of working conditions. On dead level going it was found possible to attain a speed of 10 m.p.h. in 51 secs., 15 m.p.h. in 14 secs., and 20 m.p.h. in 29 secs., on a section of the line rather remote from the main supply and where the feeder was arranged in such a manner that a rather heavy voltage drop occurred. On a subsequent test carried out on a section of the route which war properly equipped with frequently spaced feeders the acceleration figures were considerably improved, 10 m.p.h. being reached from rest in 5 secs., 20 m.p.h. in 12 secs., and 25 m.p.h. in 25 secs.

These figures give some index as to the hill-climbing capacity of the machine. Naturally with a trolleybus it is:possible to include as a test for hill-climbing only a gradient forming part of the normal passenger -route supplied with current from the overhead system. The hill chosen in the Derby circuit was situated on the Nottingham road, and although the gradient averaged but 1 in 19, the test was quite severe because there is a number of fairly acute curves which have to be taken carefully at moderate speed.

Starting at the foot at a mere B27 crawl the vehicle quickly reached 15 m.p.h. and attained a maximum of 20 m.p.h., which was held throughout the climb. This is really a very good performance, the longish incline seeming to have little effect upon the schedule time of the service buses. Restarting on the worst part of the gradient is, of course, a simple matter, the load being picked up off the brakes perfectly smoothly.

In a city such as Derby service conditions demand an average of about seven stops per mile, so the efficiency of any individual vehicle depends upon the speed with which one-seventh of a mile can be traversed. To this end we instituted a timed test of 240 yards and found that from the time the brakes were released and the power pedal -depressed until the vehicle came to rest again at the end of the measured 240 yards but 29:k secs. had elapsed. This test was repeated several times, and in each case the recorded time was less than half a minute, the vehicle attaining midway a speed of 20 m.p.h.

Efficient Braking.

One point worth recording in dealing with this matter is that the brakes, which are highly efficient, were soused that the rate of retardation measured in feet per second per second was quite moderate, in order that passengers would not be throWn forward in their seats, as might happen were the full force of the system to be utilized. Under such conditions, using only the pedalapplied system, about 90 ft. was required to halt from 20 m.p.h. On the other hand, when necessary, we found it possible to pull up to rest from 20 m.p.h. in about half the above distance, but although the retardation was perfectly progressive, it was thought that the comfort of the passengers would be affected.

Actually the brakes operate on all four wheels, the drums being 18 ins. In diameter with shoes 4i ius, wide, and the shoes faced with I-in. renewable die-pressed Ferodo fabric. The hand brake operates one pair of shoes in each drum of the leading axle of the bogie, whilst the remaining two shoes in each drum and those in the rearmost axle are operated by the latest type of Westinghouse compressed-air device. Incidentally, application of the Westinghouse air brake automatically cuts off the controller current.

Now we come to the matter of regeneration. As has already been B28

indicated, this latest Guy vehicle gives an improved figure for regeneration of current, due to the fact that the motor can be used as a generator down to speeds as low as 12 m.p.h. A polarized relay and contactor is fitted which cuts out the series winding during regeneration and gives an increased regenerative and braking effect. The magnetic control of the power pedal causes the pedal itself to be held in the regenerative position when the driver releases the foot pressure until such time as regeneration ceases through insufficient speed.

Suitable precautions are taken to protect the lighting circuit by an automatically introduced resistance in the circuit during regeneration.

At no time is the shunt circuit broken. The object of this obviously is to prevent the injurious effect that arises from breaking the shunt circuit, when a high-voltage inductive kirk occurs, probably running up to 1,000 or more volts.

Fuel-consumption Figures.

Finally, the question of running costs arises. Throughout our test, which included an enormous amount of shunting and raanceuvring to take turning-circle dimensions, braking and acceleration figures, etc., the consumption of current worked out at 2.03 units per mile. This figure is, of course, much higher than that obtaining during service conditions. Statistics provided by Mr. P. W.

Bancroft—the general manager of the transport department of Derby Corporation—show 1.88 unit per mile for the vehicles themselves, whilst the total for all purposes works out at 2.06 units per mile.

Mr. Bancroft also gave us information concerning bus and tram receipts which are rather illuminating. Taking 13 comparable weeks, the average passengers carried per single journey of a trolley-bus and a tram were 38.17 and 31.87 respectively, whilst the average speeds of all vehicles work out at 9.46 m.p.h. for the trolleybuses and 6.87 m.p.h. for the trams. In other words, besides giving a better service to the public, four trolley-buses can do the work of five trams.

Tags

Organisations: Ministry of Transport
People: P. W. Bancroft
Locations: Derby, Nottingham, London

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