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# variable moment flywheel

might help
 (+2, -1) [vote for, against]

a flywheel with square hollow spokes with sliding square nuts inside. each nut has a threaded rod through it with a gear mechanism at the center of the wheel to turn said threaded rods. this will allow a constant torque on the flywheel to have a variable moment of inertia, and thus a variable rate of rotation.

 — bleh, Aug 14 2006

bicycle with speed governor bicycle_20with_20speed_20governor
[xaviergisz, Aug 14 2006]

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...or a constant rate of rotation as momentum is changed. There will be plenty of strain on the threaded rods.
 — Ling, Aug 14 2006

 //There will be plenty of strain on the threaded rods//

that depends on the rate of rotation. perhaps linear actuators would be better?
 — bleh, Aug 14 2006

Isnt this exactly what a centrifugal Governer is in a slightly different form.
 — jhomrighaus, Aug 14 2006

no,this is within the wheel itself, essentially traveling in only 2dimensions. but yes, it is exploiting the same rotational motion properties.
 — bleh, Aug 14 2006

What [bleh] is doing, though, which is different from the Watt's governor is that Watt used rotation speed to increase moment of inertia which, in turn, reduced rotation speed - classic negative feedback. If I understand correctly, [bleh] is using external input (to the linear actuators) to control the moment of inertia, and thus rotation speed. Which is a little cool.
 — angel, Aug 15 2006

 Would you leave the weights extended at idle and the move them inwards under power --- so that there is smooth idling and better acceleration?

Or are you trying to store energy?

I was thinking forenergy storage in a system with a variable driving force. as [angel] said, the idea is to control the moment, not just have it vary with rotation.
 — bleh, Aug 18 2006

[bleh] If it's any kind of useful flywheel, no known thread could hold the nuts on. (I'm assuming your nuts have some meaningful mass if you are using them to alter the moment)
 — ConsulFlaminicus, Aug 18 2006

 from earlier (first ) anno // //There will be plenty of strain on the threaded rods//

that depends on the rate of rotation. perhaps linear actuators would be better? //
 — bleh, Aug 18 2006

 Smartarse. (-)

I saw the anno and your response.
 — ConsulFlaminicus, Aug 18 2006

not trying to be a smartarse, it just happens. :) what is a typical rate of rotation of a 'useful' flywheel? would linear actuators be better? my question was never really answered. is the [-] for being a smartarse or because you dont like the idea?
 — bleh, Aug 18 2006

 ok, obviously im no engineer, lets see if i understand this correctly.

 energy E=.5I(w^2), I is moment, w is rate of rotation. lets assume said flywheel is reved up with weights pulled to the center. when generator is engaged, a certian energy would be required to turn the generator.

 if we assume a constant negative acceleration (slowing down), we can vary the moment to maitain a constant E as w decreases . i.e. as the wheel slows down, the weights extend so that energy output stays constant.

again, i only half know what im half baking here, so im at best a quarter compitent, so please correct me if i am wrong. also, this is purely theoretical as i have no idea about materials and strains and the like.
 — bleh, Aug 18 2006

why do i always loose votes when i explain myself?
 — bleh, Aug 19 2006

 I thought that the purpose of a Watt's governor was to have the rising weights operate a throttle which would cut back on the engine's power, while imposing minimal frictional load on the engine when the speed limit was not exceeded.

Having a variable-moment flywheel could be useful for dealing with certain types of variable energy supplies or variable loading.
 — supercat, Aug 19 2006

 I’ve been thinking about this again recently. Instead of using nuts on threaded rods or linear actuators, take a ring, slice it into many equal pieces and place each piece on a pivot. These pieces could then be rotated so that they point essentially radially out from the center. They would be locked into this position by a retractable pin. The end closest to the center could then be weighted. Since a rod has a lower moment of inertia than a cylinder or ring, and the majority of the weight is nearer the center, is should be easier to rev up to speed, then when the desired RPM is reached, the pins would be retracted allowing the pieces to swing back out and snap back into their ring shape. I’m thinking the ring should be sliced non-radially so the pieces overlap when in ring shape.

Any input?
 — bleh, May 21 2007

 Your weighted rod idea can be simplified by offsetting the pivot point, so that the center of mass of each rod is inboard of the pivots while collapsed, and even with the pivots when extended.

 This will not work as you state. While it is true that this assembly will have a lesser moment of inertia in the collapsed position, thereby allowing it to be revved to a given RPM with less input, the RPM will drop as the rods are extended to the ring configuration due to the conservation of angular momentum.

TANSTAAFL.
 — Freefall, May 21 2007

damn laws of physics.
 — bleh, May 21 2007

p.s. Thanks for not using the ice skater analogy to demonstrate my ignorance.
 — bleh, May 21 2007

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