We will consider this first, as its design must govern, within certain
limits, the design of the locomotive. There are three systems of
electrical transmission available.
1. The trolley system, with overhead cable attached to insulators on
posts, to carry the current one way, the rails being used as the
“return.” This system has the disadvantages associated with a wire over
which the human foot may easily trip with disastrous effect.
2. That in which one of the wheel rails is used for taking the current
to the motor, and the other as the return. The objection to the system
is that the wheels must be insulated, to prevent short circuiting; and
this, besides causing trouble in construction, makes it impossible to
use the ordinary model rolling stock. To its credit one may place the
fact that only two rails are needed.
3. The third and, we think, best system, which has an insulated third
rail as one half of the circuit, and both wheel rails as the return,
the motor being kept in connection with the third rail by means of a
collector projecting from the frame and pressing against the top of the
third rail. The last, for reasons of convenience, is placed between the
wheel rails. We will assume that this system is to be employed.
[Illustration: FIG. 42.—Details of rails for electric track.]
Gauge.—For indoor and short tracks generally it is advisable to keep
the gauge narrow, so that sharp curves may be employed without causing
undue friction between rails and wheels. In the present instance we
specify a 2-inch gauge, for which, as also for 1-1/2 and 1-1/4 inch,
standard rolling stock is supplied by the manufacturers.
Track Construction.—It is essential that the centre rail and at least
one of the wheel rails shall have all joints bonded together to give a
clear course to the electric current, and the centre rail must be
insulated to prevent leakage and short-circuiting. Where a track is
laid down more or less permanently, the bonding is most positively
effected by means of little fish-plates, screwed into the sides of the
abutting rails; but in the case of a track which must be capable of
quick coupling-up and uncoupling, some such arrangement as that shown
in Fig. 42 is to be recommended.
Fig. 42 (a) is a cross vertical section of the track; Fig. 42 (c) a
longitudinal view; while Fig. 42 (b) shows in plan a point of junction
of two lengths of rail.
The wheel rails are made of carefully straightened brass strip 3/8 inch
wide and 1/16 inch thick, sunk rather more than 1/8 inch into wooden
sleepers (Fig. 42, a), 3-1/2 inches long and 3/4 inch wide (except at
junctions). The sleepers are prepared most quickly by cutting out a
strip of wood 3-1/2 inches wide in the direction of the grain, and long
enough to make half a dozen sleepers. Two saw cuts are sunk into the
top, 2 inches apart, reckoning from the inside edges, to the proper
depth, and the wood is then subdivided along the grain. The saw used
should make a cut slightly narrower than the strip, to give the wood a
good hold. If the cut is unavoidably too large, packings of tin strip
must be forced in with the rail on the outside. To secure the rails
further, holes are bored in them on each side of the sleeper (see Fig.
42, c), and fine iron or, brass wire is passed through these, round the
bottom of the sleeper, and made fast.
[Illustration: FIG. 43.—Tin chair for centre rail of electric track.]
The centre rail is soldered to small tin chairs, the feet of which are
pinned down to the sleepers. The top of the rails must project slightly
above the chairs, so that the current collector may not be fouled.
Junctions.—At these points one 3/4-inch sleeper is reduced to 1/2-inch
width, and the other increased to 1 inch, this sleeper being overlapped
3/8 inch by the rails of the other section. To the outsides of the
wheel rails are soldered the little angle plates, AA, BB, attached to
the sleepers by brass tacks, which project sufficiently to take the
brass wire hooks. These hooks must be of the right length to pull upon
the tacks in AA and make a good contact. The centre rails are bonded by
two strips of springy brass, riveted to one section, and forced apart
at their free end by the interposed strip. Two pins projecting from the
narrower sleeper fit into holes in the wider to keep the sections in
line at a junction.
General.—The sleepers of straight sections are screwed down to 3/4 by
1/4 inch longitudinals, which help to keep the track straight and
prevent the sleepers slipping. Sections should be of the same length
and be interchangeable. Make straight sections of the greatest
convenient length, to reduce the number of junctions. Sleepers need not
be less than 6 inches apart. Fix the sleepers on the longitudinals
before hammering the rails into the slots.
[Illustration: FIG. 44.—Laying out a curve for electric track.]
Curves.—A simple method of laying out a semi-circular curve is shown in
Fig. 44. Sleepers and longitudinals are replaced by 1/2-inch boards, 8
inches wide. Three pieces, about 32 inches long each, have their ends
bevelled off at an angle of 60 degrees, and are laid with their ends
touching. Two semi-circles of 24 and 22 inch radius are drawn on the
boards to indicate the positions of the rails, and short decapitated
brass nails are driven in on each side of a rail, about an inch apart,
as it is laid along one of these lines. (See Fig. 44. A.) The inside
nails must not project sufficiently to catch the wheel flanges. The
spring of the brass will prevent the rail falling out of place, but to
make sure, it should be tied in with wire at a few points. The centre
rail should on the curves also be 3/8 inch deep, and raised slightly
above the bed so as to project above the wheel rails. The method
already described of bonding at joints will serve equally well on
curves. If the outer rail is super-elevated slightly, there will be
less tendency for the rolling stock to jump the track when rounding the
curve.
When the rails are in place the boards may be cut with a pad-saw to
curves corresponding with the breadth of the track on the straight. If
the boards incline to warp, screw some pieces of 1/8-inch strip iron to
the under side across the grain, sinking the iron in flush with the
wood.
The brass strip for the rails costs about one penny per foot run. Iron
strip is much cheaper, but if it rusts, as it is very likely to do, the
contact places will need constant brightening.
Points.—Fig. 45 shows the manner of laying out a set of points, and
connecting up the rails. The outside wheel rails, it will be seen, are
continuous, and switching is effected by altering the position of the
moving tongues, pivoted at PP, by means of the rod R, which passes
through a hole in the continuous rail to a lever or motor of the same
reversible type as is used for the locomotive. If a motor is employed,
R should be joined to a crank pin on the large driven cog—corresponding
to that affixed to the driving wheel (Fig. 47)—by a short rod. The pin
is situated at such a distance from the axle of the cog wheel that a
quarter of a revolution suffices to move the points over. The points
motor must, of course, have its separate connections with the “central
station.” To show how the points lie, the rod R also operates a
semaphore with a double arm (Fig. 46), one end of which is
depressed—indicating that the track on that side is open—when the other
is horizontal, indicating “blocked.” The arms point across the track.
[Illustration: FIG. 45.—Points for electric railway.]
Details.—The tongues must be bevelled off to a point on the sides
respectively nearest to the continuous rails. The parts AA are bent out
at the ends to make guides, which, in combination with the safety
rails, will prevent the wheels jumping the track. Care should be taken
to insulate centre rail connecting wires where they pass through or
under the wheel rails.
It is advisable to lay out a set of points, together with motor and
signals, on a separate board.
[Illustration: Fig. 46.—Double-armed signal, operated by points.]
Preservation of Track.—All the wooden parts of an outdoor track should
be well creosoted before use.
The Electric Locomotive.
An elevation and a plan of this are given in Fig. 47. The two pairs of
wheels are set close together, so that they may pass easily round
curves.
[Illustration: Fig. 47.—Plan and elevation of electric locomotive.]
The Motor.—A motor of ordinary type, with electro field magnets, is
unsuitable for traction, as it cannot be reversed by changing the
direction of the current, unless a special and rather expensive type of
automatic switch be used. While a motor of this kind is, in conjunction
with such a switch, the most efficient, the motor with permanent field
magnets is preferable as regards cost and ease of fixing. It can be
reversed through the rails. The armature or revolving part must be
tripolar to be self-starting in all positions.
A motor of sufficient power can be bought for half a crown or less—in
any case more cheaply than it can be made by the average amateur.
The motor used for the locomotive illustrated was taken to pieces, and
the magnet M screwed to a strip of wood 1-5/8 inches wide; and for the
original armature bearings were substituted a couple of pieces of brass
strip, HH, screwed to two wooden supports, SS, on the base, E (Fig. 47,
a). It was found necessary to push the armature along the spindle close
to the commutator piece, C, and to shorten the spindle at the armature
end and turn it down to the size of the original bearing, in order to
bring the motor within the space between the wheels.
The place of the small pulley was taken by an 8-toothed pinion wheel,
engaging with a pinion soldered to the near driving wheel, the diameter
of which it exceeded by about 3/16 inch. The pair, originally parts of
an old clock purchased for a few pence, gave a gearing-down of about 9
times.
The position of the driven wheels relatively to the armature must be
found experimentally. There is plenty of scope for adjustment, as the
wheels can be shifted in either direction longitudinally, while the
distance between wheel and armature centres may be further modified in
the length of the bearings, BE. These last are pieces of brass strip
turned up at the ends, and bored for axles, and screwed to the under
side of the base. To prevent the axles sliding sideways and the wheels
rubbing the frame, solder small collars to them in contact with the
inner side of the bearings.
The Frame.—Having got the motor wheels adjusted, shorten E so that it
projects 2 inches beyond the centres of the axles at each end. Two
cross bars, GG, 3-1/2 inches long, are then glued to the under side of
E, projecting 1/8 inch. To these are glued two 3/8-inch strips, FF, of
the same length as E. A buffer beam, K, is screwed to G. A removable
cover, abedfg, is made out of cigar-box wood or tin. The ends rest on
GG; the sides on FF. Doors and windows are cut out, and handrails,
etc., added to make the locomotive suggest the real thing—except for
the proportionate size and arrangement of the wheels.
Electrical Connections.—The current collector, CR, should be well
turned up at the end, so as not to catch on the centre rail joints, and
not press hard enough on the rail to cause noticeable resistance. The
fixed end of CR is connected through T2 with one brush, B, and both
wheel bearings with T1.
[Illustration: FIG. 48.—Reversing switch.]
Electrical Fittings.—The best source of power to use is dry cells
giving 1-1/2 to 2 volts each. These can be bought at 1s. apiece in
fairly large sizes. Four or five connected in series will work quite a
long line if the contacts are in good condition.
A reversing switch is needed to alter the direction of the current
flow. The construction of one is an exceedingly simple matter. Fig. 48
gives a plan of switch and connection, from which the principle of the
apparatus will be gathered. The two links, LL, are thin springy brass
strips slightly curved, and at the rear end pivoted on the binding
posts T1 T2. Underneath the other ends solder the heads of a couple of
brass nails. The links are held parallel to one another by a wooden
yoke, from the centre of which projects a handle. The three contacts C1
C2 C3 must be the same distance apart as the centres of the link heads,
and so situated as to lie on the arcs of circles described by the
links. The binding post T3 is connected with the two outside
contacts—which may be flat-headed brass nails driven in almost flush
with the top of the wooden base—by wires lying in grooves under the
base, and T4 with the central contact. As shown, the switch is in the
neutral position and the circuit broken.
[Illustration: Fig. 49.—Multiple battery switch.]
Multiple Battery Switch.—To control the speed of the train and
economize current a multiple battery switch is useful. Fig. 49 explains
how to make and connect up such a switch. The contacts, C1 to C5, lie
in the path of the switch lever, and are connected through binding
posts T1 to T6 with one terminal of their respective cells. The cells
are coupled up in series to one another, and one terminal of the series
with binding posts T0 and T6. By moving the lever, any number of the
cells can be put in circuit with T7. The button under the head of the
lever should not be wide enough to bridge the space between any two
contacts. Change the order of the cells occasionally to equalize the
exhaustion.
[Illustration: FIG. 50.—Adjustable resistance for controlling current.]
Resistance.—With accumulators, a “resistance” should be included in the
circuit to regulate the flow of current. The resistance shown in Fig.
50 consists of a spiral of fine German silver wire lying in the grooved
circumference of a wood disc. One of the binding posts is in connection
with the regulating lever pivot, the other with one end of the coil. By
moving the lever along the coil the amount of German silver wire, which
offers resistance to the current, is altered. When starting the motor
use as little current as possible, and open the resistance as it gets
up speed, choking down again when the necessary speed is attained.
General.—All the three fittings described should for convenience be
mounted on the same board, which itself may form the cover of the box
holding the dry cells or accumulators.