An Ingenious Four-track DRIVING BOGIE
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The Latest Robey Steam Wagon is a Rigid Six wheeler, Each of the Four Driving Wheels Occupying a Separate Track.
FAMOUS for the efficiency and relicbilitY— of its four-wheeled steam wagons and tractors, the old-established concern of Robey and lo., Ltd., Lincoln, has now produced a six-wheeled 12-ton -Wagon which has the .peculiar feature that the four wheels, of the driving bogie run ...separate'tracks. . The bogie; Whie.h is fully protected by patents, is an interesting piece of engineering and
it has many advantages. • Whilst the forward wheels are disposed outside the Chassis frame, the rearmost wheels have an extremely narrow , track and are actually placed within the
main frame members. Obviously, such a practice means that less wear is caused to, the road surface over which. the vehicle travel's? .and, better adhesion is obtained oh had -siirfaceS,. such as are exp,erienced. when working in qUarrieS and sand„ pits, far the reason that the rearmost wheels grip upon -fresh ground instead Of reeking use ofthe ruts already formed by. the wheels Of the forward
driving axle. . .
. Again, hauliers 'who have suffered the. difficulties of travelling .over tarred roads. (especially those which have recently B36 been sprayed) with solid-tyre sixwheelers, will appreciate the advantage offered by the four-track bogie. It appears that when solid tyres become hot through travelling at speed under load, the forward tyres heat the road surface just sufficiently for the tyres of the rear wheels to pick up the tar..
Perhaps a more important advantage, however, is that the tyre slip when cornering, which is inevitable in theca-se of rigid six-wheelers, is, by the design of this bogie, very considerably reduced. Two factors combine towards this reduction: first, the narrow track of the rearmost wheels, being less than half that of the forward driving wheels, makes the degree of drag of the final wheels proportionately less than it
would be secondly, the drag is reduced by the fact that the two axles tof the bogie are very much closer together than would be possible if both pairs of wheels had the same track.
Dealing now with the design of the bogie, it is a self-contained unit anchored to the frame by orthodox semi-elliptic springs and two radius rods, and it makes use of the eountershaftwhiekis employed fo&r the single-chain drive of the standard Robey machine. From this countershaft a single roller chain on the near side conveys the drive to a sprocket mounted on the bogie-unit casing (which is of cast steel) in front of the forward axle. Thence power is conveyed by Pinion to a gear wheel bolted direct to the first differential.
The power is then taken from a bevel wheel, similarly attached to the differential, through' a bevel pinion and propeller Shaft which drives the back axle by means of a similar bevel pinion and wheel to those on the forward axle. An important feature is that the two rear wheels are mounted on a trunnion shaft which allows them to accommodate themselves to the inequalities of the road.
Thus perfect articulation of all wheels is ensured ; it is the principle. of the three-legged stool. The rear wheels are so close together.that a differential need not be employed, and in the case of the machine which we are describing it has actually not been fitted.
• As regards dimensions, the main track of the, rear wheels is 1 ft. Oi ins., that of the front driving wheels be_iing:5. ft.
p The wheels :are interchangeable, each carrying : 850-mm..by 160.-inni. twin solid tyres. The wheelbase of the bogie is 3 ft. 5 ins.
With regard to braking, the standard Robe k singlershee brakes which have been so successful hitherto 'arc ecaployed; those. operating on the fortra:rd axle' being actuated by the pedal. and those on the rearmost wheels being controlled by the hand lever.. To obtain good leverage, the brake drums "are made as' large. as possible, their actual diameter being no less than 2 ft T ins.
As regards the other: details of the machine, these call:for no description since they are virtually identical with' those of the }Obey 6-ton wagon. '
A wagon equipped with the bogie has been supplied to the Tilbury Contracting' and Dredging Co.; Ltd.; of Maidstone,' thid. it embodies a ,tipPinggear of -the' telescopic-hydraulic-ram type worked from 'the boiler feed 'pump. The Wheel-. base of this machine (to bogie centre) is 15 ft: 5 ins:, and the oirerall length 24 ft. Bins.The all--steel body measures 12 ft: by :T ft. by 3 ft: 6 ins. deep, this
fkize : being for loadS' , of tar . inacadam or similar material. .