By M. HOLROYD SMITH.
Last year, when I had the pleasure of reading a paper before you on my new
system of electric tramways, I ventured to express the hope that before
twelve months had passed, "to be able to report progress," and I am happy
to say that notwithstanding the wearisome delay and time lost in fruitless
negotiations, and the hundred and one difficulties within and without that
have beset me, I am able to appear before you again and tell you of
advance.
[Illustration: FIG. 1]
Practical men know well that there is a wide difference between a model and
a full sized machine; and when I decided to construct a full sized tramcar
and lay out a full sized track, I found it necessary to make many
alterations of detail, my chief difficulty being so to design my work as to
facilitate construction and allow of compensation for that inaccuracy of
workmanship which I have come to regard as inevitable.
In order to satisfy the directors of a tramway company of the practical
nature of my system before disturbing their lines, I have laid, in a field
near the works of Messrs. Smith, Baker & Co., Manchester, a track 110 yards
long, 4 ft. 8½ in. gauge, and I have constructed a full sized street
tramcar to run thereon. My negotiations being with a company in a town
where there are no steep gradients, and where the coefficient of friction
of ordinary wheels would be sufficient for all tractive purposes, I thought
it better to avoid the complication involved in employing a large central
wheel with a broad surface specially designed for hilly districts, and with
which I had mounted a gradient of one in sixteen.
[Illustration: FIG. 2]
But as the line in question was laid with all the curves unnecessarily
quick, even those in the "pass-bies," I thought it expedient to employ
differential gear, as illustrated at D, Fig. 1, which is a sketch plan
showing the mechanism employed. M is a Siemens electric motor running at
650 revolutions per minute; E is a combination of box gearing, frictional
clutch, and chain pinion, and from this pinion a steel chain passes around
the chain-wheel, H, which is free to revolve upon the axle, and carries
within it the differential pinion, gearing with the bevel-wheel, B², keyed
upon the sleeve of the loose tram-wheel, T², and with the bevel-wheel, B¹,
keyed upon the axle, to which the other tram-wheel, T¹, is attached. To the
other tram-wheels no gear is connected; one of them is fast to the axle,
and the other runs loose, but to them the brake is applied in the usual
manner.
The electric current from the collector passes, by means of a copper wire,
and a switch upon the dashboard of the car, and resistance coils placed
under the seats, to the motor, and from the motor by means of an adjustable
clip (illustrated in diagram, Fig. 2) to the axles, and by them through the
four wheels to the rails, which form the return circuit.
[Illustration: FIG. 3]
I have designed many modifications of the track, but it is, perhaps, best
at present to describe only that which I have in actual use, and it is
illustrated in diagram, Fig. 3, which is a sectional and perspective view
of the central channel. L is the surface of the road, and SS are the
sleepers, CC are the chairs which hold the angle iron, AA forming the
longitudinally slotted center rail and the electric lead, which consists of
two half-tubes of copper insulated from the chairs by the blocks, I, I. A
special brass clamp, free to slide upon the tube, is employed for this
purpose, and the same form of clamp serves to join the two ends of the
copper tubes together and to make electric contact. Two half-tubes instead
of one slotted tube have been employed, in order to leave a free passage
for dirt or wet to fall through the slot in the center rail to the drain
space, G. Between chair and chair hewn granite or artificial stone is
employed, formed, as shown in the drawing, to complete the surface of the
road and to form a continuous channel or drain. In order that this drain
may not become choked, at suitable intervals, in the length of the track,
sump holes are formed as illustrated in diagram, Fig. 4 These sump holes
have a well for the accumulation of mud, and are also connected with the
main street drain, so that water can freely pass away. The hand holes
afford facility for easily removing the dirt.
In a complete track these hand holes would occasionally be wider than shown
here, for the purpose of removing or fixing the collector, Fig. 5, which
consists of two sets of spirally fluted rollers free to revolve upon
spindles, which are held by knuckle-joints drawn together by spiral
springs; by this means the pressure of the rollers against the inside of
the tube is constantly maintained, and should any obstruction occur in the
tube the spiral flute causes it to revolve, thus automatically cleansing
the tubes.
[Illustration: FIG. 4]
The collector is provided with two steel plates, which pass through the
slit in the center rail; the lower ends of these plates are clamped by the
upper frame of the collector, insulating material being interposed, and the
upper ends are held in two iron cheeks. Between these steel plates
insulated copper strips are held, electrically connected with the collector
and with the adjustable clip mounted upon the iron cheeks; this clip holds
the terminal on the end of the wire (leading to the motor) firmly enough
for use, the cheeks being also provided with studs for the attachment of
leather straps hooked on to the framework of the car, one for the forward
and one for backward movement of the collector. These straps are strong
enough for the ordinary haulage of the collector, and for the removal of
pebbles and dirt that may get into the slit; but should any absolute block
occur then they break and the terminal is withdrawn from the clip; the
electric contact being thereby broken the car stops, the obstruction can
then be removed and the collector reconnected without damage and with
little delay.
[Illustration: FIG. 5]
In order to secure continuity of the center rail throughout the length of
the track, and still provide for the removal of the collector at frequent
intervals, the framework of the collector is so made that, by slackening
the side-bolts, the steel plates can be drawn upward and the collector
itself withdrawn sideways through the hand holes, one of the half-tubes
being removed for the purpose.
Fig. 6 illustrates another arrangement that I have constructed, both of
collector and method of collecting.
[Illustration: FIG. 6]
As before mentioned, the arrangement now described has been carried out in
a field near the works of Messrs. Smith, Baker & Co., Cornbrook Telegraph
Works, Manchester, and its working efficiency has been most satisfactory.
After a week of rain and during drenching showers the car ran with the same
speed and under the same control as when the ground was dry.
This I account for by the theory that when the rails are wet and the tubes
moist the better contact made compensates for the slight leakage that may
occur.
At the commencement of my paper I promised to confine myself to work done;
I therefore abstain from describing various modifications of detail for the
same purpose. But one method of supporting and insulating the conductor in
the channel may be suggested by an illustration of the plan I adopted for a
little pleasure line in the Winter Gardens, Blackpool.
[Illustration: FIG. 7.]
Fig. 7. There the track being exclusively for the electric railway, it was
not necessary to provide a center channel; the conductor has therefore been
placed in the center of the track, and consists of bar iron 1¼ in. by ½
in., and is held vertically by means of studs riveted into the side; these
studs pass through porcelain insulators, and by means of wooden clamps and
wedges are held in the iron chairs which rest upon the sleepers. The iron
conductors were placed vertically to facilitate bending round the sharp
curves which were unavoidable on this line.
The collector consists of two metal slippers held together by springs,
attached to the car by straps and electrically connected to the motor by
clips in the same manner as the one employed in Manchester.
I am glad to say that, notwithstanding the curves with a radius of 55 feet
and gradients of 1 in 57, this line is also a practical success.
* * * * *