h a l f b a k e r y"Not baked goods, Professor; baked bads!" -- The Tick
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The idea of using a flywheel for storing energy in bikes is
often suggested (see for example my idea 'bike hub with
two motors') but has a significant flaw - the gyroscopic
effect of the flywheel. The obvious solution is to mount the
flywheel on a gimbal, but then what mechanism can be
used
to store and retrieve the energy to and from the
flywheel?
I've come up with a flywheel gimbal that allows easy
storage and retrieval of energy. See illustration first, then
read on.
The ring flywheel (blue) sits on rails (grey). Cams (purple)
are slidably mounted on an inside track in the flywheel,
thus allowing each cam to slide a limited distance
circumferentially. The flywheel and rails both spin
together. The flywheel (not shown to scale) is heavier than
the rails and thus has most of the rotational inertia.
When the bike tilts the ring flwheel stays vertical as it
slides on the outside of the rails. The cams move
circumferentially and their spacing changes - 'bunching up'
where the edge of the ring is closest to the ends of the
rails.
There are a few problems with this idea: the rails are
adding 'ungimballed' rotational inertia to the system; lots of
friction; the gimbal only allows limited range of rotation
(fine for tilt, but not so much for turning).
This idea could also be used as a CV joint.
illustration
http://imgur.com/a/9Svx9
[xaviergisz, Oct 28 2012]
"The Ringworld is unstable..."
http://lifegivesmel...m/2011/11/endo1.jpg
[normzone, Oct 29 2012]
(?) An example of a flywheel electric load leveling/backup device
http://www.beaconpo...smart-energy-25.asp
[CraigD, Oct 31 2012]
The Chrysler Patriot and possible F1 flywheel specs
http://www.allpar.com/model/patriot.html
[CraigD, Oct 31 2012]
[link]
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I like this insofar as I understand it! + |
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I'm wondering what prevents the flywheel from just falling off entirely, not turning axially, just sliding off to the side.You could add a larger element that rides inside the cage and prevents this. |
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Thus far it looks like a promising idea. |
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hmm... 'k, first off you could get away with only having three curved whatsises, but I think the main thing is that as the onion flourette turns it will slide up and down on the flywheel once each revolution... that and it will be transferring power at an angle so you havent lost precession so much as moved it around a bit. |
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Big, heavy outer ring. Three thin, stiff spokes connected to a ball. Ball clamped from above and below in a cage with 3 slots through which the spokes pass. |
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Probably not too hard to get +/- 45 degrees freedom about the axis. |
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Energy transfer is via the cage contact with the spokes, which have bearing surfaces - there could be roller bearings around the base of the spokes where they contact the cage to minimise frictional losses. |
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Much less machining. Simple. Fewer contact surfaces. Can be made arbitrarily large or small. |
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Considering the limited range of tilt, it seems like this idea is better if the flywheel is spining with a vertical axis (as in your illustrations). then oyu don't have to worry about turning, though you will have to worry about overcomming turning forces as you take energy out or put it back into your flywheel (unless you had a pair). |
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However I don't see any mechanism to keep the flywheel centered on the rails. When run as shown in your illustrations, it looks like the ring will just fall to the floor. |
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I agree WcW, a stop will be needed at the ends of the rails
so it doesn't slip off. Also, there will need to be something
to ensure the flywheel is constrained to the surface of the
rails (the cams could be shaped to perform this function). |
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Scad, I don't think the flywheel needs to be 'biased' to the
centre. Lets say the flywheel is stationary and tilting to one
side; once the flywheel starts to rotate I think it will
wobble for a bit, but then centre itself by centrifugal
force. |
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FT, I'm not sure what effect precession would have on the
flywheel. It's possible it could become unstable. I agree a
smaller number of rails could be used. |
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I still think turning will be the biggest problem with this
idea. The flywheel (mounted vertically) has two axes of
freedom of rotation: tilt and turn. A bike can only tilt in a
limited range, but obviously there is no limitation on
turning. The solution to this problem is fairly rudimentary:
dump energy (i.e. brake the flywheel) if turning outside a
limited range is detected. |
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I had envisaged that the flywheel would only be used
temporarily to store small amounts of energy - just enough
to slow a rider from 20km/h to rest and then back up to
speed again - thus the need for a large range of tilt/turn
angle is lessened. |
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8th, can't visualise what you're talking about yet. I'll think
about it for a while and try and illustrate it. |
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there's also pitch as a 3rd axis, ie: going uphill or downhill. The precessional forces will come into play while you're loading or unloading the gyro when it and the mercator-ball aren't lined up. |
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//The obvious solution is to mount the flywheel on a gimbal, but then what mechanism can be used to store and retrieve the energy to and from the flywheel?// |
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An electrical motor/generator will allow a relatively frictionless system with full gymbalness. |
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Flywheel storage involving getting and putting energy into the flywheel using essentially the same technology as brushless electric motor/generators, is pretty well-baked technology, though mostly in large, heavy load leveling and backup power systems. (see link) |
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It’s had a long but checkered history in smaller flywheels mounted in vehicles, perhaps most famously in the Chrysler Patriot Le Mans racecar. The need to minimize mass necessitating reducing safety margins, while necessarily being close to people, and a catastrophic failure that involves lots of high-speed shrapnel, prevented the Patriot from being accepted when it was built and briefly raced in the early 1990s. (see link) |
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I’d not followed flywheel power for a couple of years, and see from the link that it may be up for a revival, again for racecars, this time F1. Rather than the big 67 kg flywheel used in the Patriot, the F1 proposal is said to be for a smaller, 5 kg, 400000 J one. At a glance, such a system seems nearly ideal for a bike or other human-powered vehicle. |
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Could this keep a 'ring of cameras' (think multiple RasPi
camera modules mounted on the outside of the ring) stable
against the horizon? |
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Of course, RasPi camera modules need RasPi boards and
power, so this won't work at the moment. But the future
may find this useful for VR video recording. The entire setup
could even be mounted on the outside of a helmet. |
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