The fly wheel may be a disc of wood.
Oil all the rubbing parts slightly. Connect T1 to one terminal of the
battery, T2 to the coil, and the other terminal of the battery to the
coil. Set the engine going. If it refuses to run, make sure that B1 is
pressing against D. The speed of the engine may possibly be improved by
careful adjustment of B2 and an alteration in the setting of the crank,
and will certainly be accelerated by increasing the number of battery
cells.
The cost of the engine described was about 1s, 3d., exclusive of the
battery.
XII.
AN ELECTRIC ALARM CLOCK.
Anybody who possesses an alarm clock with an external gong, an electric
bell, and a battery, may easily make them combine to get the drowsiest
of mortals out of bed on the chilliest of winter mornings. The
arrangement has as its secondary advantages and capabilities—
(l) That the clock can be placed where its ticking will not disturb the
person whom it has to arouse in due course (some of the cheaper clocks
are very self-advertising);
(2) That one clock can be made to operate any number of bells in
different parts of the house.
The main problem to be solved is, how to make the alarm mechanism of
the clock complete an electric circuit when the alarm “goes off.”
If you examine an alarm clock of the type described, you will find that
the gong hammer lies against the gong when at rest, and that its shaft
when in motion vibrates to and fro about a quarter of an inch.
[Illustration: FIG. 89.—Plan of release gear of electric alarm, as
attached to clock.]
Fig. 39 shows a. method of utilizing the movement of the hammer. A
piece of wood, 2 inches long, wide enough to fill the space between the
rear edge of the clock and the hammer slot, and 1/2 inch thick, has its
under side hollowed out to the curvature of the clock barrel. This
block serves as a base for two binding posts or terminals, T1 T2. A
vertical slit is made in T1 and in this is soldered [to] one end of a
little piece of spring brass strip, 1 inch long and 1/4 inch wide. To
the back of the other end of the strip solder a piece of 1/20 inch
wire, projecting l inch below the strip. The strip must be bent so that
it presses naturally against T2. A little trigger, B, which you can cut
out of sheet brass, is pivoted at a, where it must be raised off the
base by a small washer. It projects 1/4 inch beyond the base on the
gong support side. A square nick is cut in it at such a distance from a
that, when the wire spike on C is in the nick, the strip is held clear
of T2. The other end of the trigger, when the trigger is set, must be
1/8 inch from the shank of the alarm hammer—at any rate not so far away
that the hammer, when it vibrates, cannot release C from the nick.
To fix the base on to the top of the clock, the works must be removed
(quite an easy matter to accomplish) and holes bored for a couple of
screws put through from the inside. If the underside of the base is not
quite correctly curved, take care not to force in the screws far enough
to distort the barrel. It is advisable to do the fitting of the parts
of the release after the base has been fixed, and before the works are
replaced. The position of the hammer shaft can be gauged accurately
enough from the slot in the case.
The tails of the terminals T1 T2 must be truncated sufficiently not to
penetrate the base and make contact with the barrel, or a “short
circuit” will be evident as soon as the battery is connected up.
[Illustration: Fig. 40.—Electric alarm releaser, as attached to
separate wooden clock casing.]
If the bell, battery, and clock are in the same room, a single dry cell
will give sufficient current; but if the circuit is a long one, or
several bells have to be operated, two or more cells will be required.
An Alternative Arrangement.—Should the reader prefer to have the clock
quite free from the release—and this is certainly convenient for
winding and setting the alarm—he should make a little wooden case for
the clock to stand in, just wide enough to take the clock, and the back
just as high as the top of the barrel. The release is then attached to
a little platform projecting from the back, care being taken that the
lever is arranged in the correct position relatively to the hammer when
the clock is pushed back as far as it will go (Fig. 40).
If a self-contained outfit is desired, make the case two-storied: the
upper division for the clock, the lower for the cell or cells. The bell
may be attached to the front. A hinged fretwork front to the clock
chamber, with an opening the size of the face; a door at the back of
the cell chamber; and a general neat finish, staining and polishing,
are refinements that some readers may like to undertake.
Setting the Alarm.—A good many alarm clocks are not to be relied upon
to act within a quarter of an hour or so of the time to which they are
set. But absolute accuracy of working may be obtained if the clock
hands are first set to the desired hour, and the alarm dial hand
revolved slowly till the alarm is released. The hands are then set at
the correct time, and the alarm fully wound.
XIII.
A MODEL ELECTRIC RAILWAY.
The rapid increase in the number of electrically worked railways, and
the substitution of the electric for the steam locomotive on many
lines, give legitimate cause for wondering whether, twenty or so years
hence, the descendants of the “Rocket” will not have disappeared from
all the railways of the world, excepting perhaps those of
transcontinental character.
[Illustration: Fig. 41.—Electric Locomotive.]
The change is already spreading to model plant, and not without good
reason, as the miniature electric railway possesses decided advantages
of its own. Instead of having to chase the locomotive to stop or
reverse it, one merely has to press a button or move a switch. The
fascinations of a model steam locomotive, with its furnace, hissing of
steam, business-like puffings, and a visible working of piston and
connecting rods, are not to be denied, any more than that a full-sized
steam locomotive is a more imposing object at rest or in motion than
its electric rival. On the other hand, the ease of control already
noticed, and the absence of burning fuel, water leakage, smoke and
fumes, are strong points in favour of the electric track, which does no
more harm to a carpet than to a front lawn, being essentially clean to
handle. Under the head of cost the electric locomotive comes out well,
as motors can be purchased cheaply; and connecting them up with driving
wheels is a much less troublesome business than the construction of an
equally efficient steamer. One may add that the electric motor is ready
to start at a moment’s notice: there is no delay corresponding to that
caused by the raising of steam.