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I am (as you may know) a bit of a watch geek.
Many of my watches are self-winding, and the
mechanism
is both simple and elegant. A single rotor (effectively, a
half-disc) swings two and fro as you move. A beautifully
simple gear mechanism converts this movement - in
_either_ direction -
into winding the mainspring.
It's a very nice system (watchmakers were harvesting
"wasted" energy centuries before we thought of
attaching
generators to hamster wheels), but not perfect.
Because
of the large reduction in gearing needed to wind the
mainspring, and because of the need to change the
gearing
between forward and backward turns of the rotor, there
is
some lost motion in the system.
Some arm movements will set the rotor spinning, in
which
case the lost motion is negligible. But many other
movements just swing the rotor back and forth, with
considerable losses at each swing. If the rotor were of a
different diameter, it would be set spinning at different
frequencies, but would still have "dead spots" where it
just
swings back and forth.
What is needed, therefore, is a multi-rotor system.
Instead of a single rotor (which, as mentioned, is like a
half-disc, weighted around its edge), we have two or
more
concentric rotors. Each has a different diameter (again,
with its edge weighted), and they fit together like a
series
of nested jar-lids. Crucially, the different diameters will
be set spinning by different arm movements.
The clutch/gear system necessary to capture energy
from
whichever rotor is turning the most will be a little
complex, but not unduly so. In fact, it can be based on
the same principle as the existing single-rotor, direction-
rectifying clutch.
The result will be more efficient energy capture. This,
of
course, is of little use on a regular watch (which is
adequately powered by normal self-winding
mechanisms),
but becomes more important for watches with greater
numbers of complications which, at present, cannot be
adequately maintained by a simple self-winding
mechanism. Also, given that people will spend extra
thousands of pounds for a watch with a largely
decorative tri-axial tourbillon, a multi-rotor self-winder
ought to be worth a fair bit.
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It seems to me that the energy generated is proportional
to the off center mass of the flywheel. While dividing up
the mass between 3 different flywheels with different
resonant frequencies might help some (15 - 40% maybe?),
if we could increase the mass, we would get a linear
increase in energy. |
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Assuming we don't want to change the overall size or
weight of the watch, what we need to do is take
advantage of the existing mass. I can't see any way to
use the mass of the case, watch face, and crystal which
by convention are expected to remain stationary relative
to the wrist, but everything else is fair game. Therefore
the gearing mechanism needs to be miniaturized to fit in
a little less than 1/2 the volume, but then constructed
out of depleted uranium the bring the weight back to
where it started. Have that mounted off center so that
most of the clockwork can swing around inside the case
that is approximately half empty. Some clever gearing
will be necessary to keep the hands steady and interface
with the stationary knob, but that would just be some
variations on a differential gear. |
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//the energy generated is proportional to the off
center mass of the flywheel.// |
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Yesish, but a proportion of the motion is lost. In a
simple but well-made rotor (with bidirectional
gearing), I would guess that something like 20
degrees of motion is lost. Hence, if the rotor is
swinging back and forth through a 120 degree arc,
only 80 degrees of that movement will be
harnessed. |
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In contrast, if you can get the rotor swinging, you
lose 20 degrees initially, but then all further
rotation is available for winding. |
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Perhaps a combined blood pressure cuff and watch, built with hydraulic powered means to measure time and pressures. Thump bump about once a second. |
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Sales would increase if your Doctor had to prescribe the watch for you. |
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"But it stopped short — never to go again — When the old man died." |
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// we have two or more concentric rotors.//
What about 3 orthogonal axes for rotating masses, winding a single spring ? Any reciprocating, circular motion would add energy to the system, and linear accelerations too, to some extent. Not suitable for a watch, but maybe usable for other applications |
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Orthogonal rotors are an excellent idea. And, with
the current fashion to make watches as big as
possible, probably feasible. |
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I would like to see this idea applied first to
long-case grandfather clocks on ships, which could easily be made to recover energy from the rocking and pitching motion of the waves. This would save money for the operators of ocean liners who would no longer have to clock-winders. |
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