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In terms of energy storage, a flywheel can weigh about the same
as a battery pack and store an equivalent amount of energy (see
first link), but the energy-conversion efficiency, between stored
energy and dynamic energy is much better for a flywheel (95%)
than for a battery (80%?). Since higher
efficiency means "less
waste", the net effect is that the flywheel stores more *usable*
energy than the battery.
So, depending on how much energy you actually want a particular
device to have usefully available, before recharging it, the
flywheel can weigh a bit less than the battery pack.
See the second link for one design of a canister vacuum cleaner.
It could easily hold a horizontally-mounted flywheel. It only
needs to be plugged into a wall outlet to recharge the flywheel.
You don't have to worry about a limited number of
charge/discharge cycles, before replacing a battery pack. And
there should be power sufficient to run the vacuum cleaner all
over the house, cordlessly.
Flywheel powered car proposal
The article contains significant information about what sorts of flywheels work best. [Vernon, Dec 17 2014]
Canister vacuum example
As mentioned in the main text. [Vernon, Dec 17 2014]
||There's plenty of conflicting data, but there seems to be
more information favouring that flywheels have very
good power density and relatively poor energy density.
||But in your vacuum application, the flywheel could be
made to pump air by magnetic coupling to an impeller,
which would minimise losses and simplify the design.
||You'd want to park it on a "spin up" station, offloading the
motor from vacuum entirely, and have the direct coupling
to the impeller.
||The big concern is that really energy dense flywheels
require significant armoring around themselves in order to
be safe in case of materials failure, and they don't react
well to shocks (such as getting bounced down the stairs).
Both of these limit their utility in small consumer
applications like this.
||Would gyroscopic effects make it hard to manoeuvre?
||I think a vertical axis flywheel would also allow the
vacuum cleaner to rotate easily around the vertical axis.
An interesting side effect would be that the vacuum
cleaner would fall down the stairs while remaining sort
of vertical...ie it would precess down.
||[hippo], on a flat horizontal surface a horizontal flywheel
offers no extra resistance to being moved about in any
horizontal direction. The canister would attempt to
remain horizontal when going up/down stairs. It would be
best if the canister had some sort of step-support legs that
could be deployed in the middle of a stairway, to keep it
||// Would gyroscopic effects make it hard to manoeuvre? //
||Use a pair of contrarotating flywheels.
||//Use a pair of contrarotating flywheels//
||You actually end up needing three, 1x weight rotating in
one direction, 2x weight rotating in the other, and then 1x
in the first direction.
||A pair tends to produce a very sharp rotation around the
midpoint between them.
||What [MechE] said in his first anno. To enable
high RPMs with a direct connection to the
impeller, perhaps a form of Tesla turbine would be
appropriate. The spin-up station could operate by
being the stator of a switched reluctance motor
and the flywheel could be the rotor. I think it is
possible to design a switched reluctance motor
that has a non-rotating steel shell between the
rotor and stator, so that can be a bit of
containment. I guess a Kevlar or other composite
containment shell could work with a more
standard AC induction flywheel. The spin-up
station could also function as a spin-down station,
so when you're done you can put some of the
power pack onto the grid and not hear your
vacuum spinning for a long time after you're done.
||Counter-rotating flywheels are fine, but don't they
put a lot of stress on the bearings whenever the
system rotates? It seems like it would be best to
allow the flywheel to rotate freely on all axis inside
the vacuum. Of course that might lend itself
better to a system that doesn't have a direct
connection between impeller and flywheel.
||//If on the same axle which they don't necessarily have to
||If they aren't on the same axle, you just shift where the
torque is located.