Flywheel Generators

[jake]

It seems that everywhere I look, someone has posted the equations of how much energy you can get OUT of a flywheel...but nobody has the formula for how much energy it takes to get the thing wound up in the first place... According to Newton's laws it takes less energy to keep an object moving than it takes to GET it moving...in the case of a flywheel, just how much energy are we talking about? I believe that this formula would be the single most helpful thing to the cause of an overunity flywheel generator. If we know how much energy it takes to KEEP it spinning, we can then figure out how much of a load we can take off of it to power an electric motor to keep it going...if anyone can find this formula please post it here!

The answer is quite simple.

from http://www.upei.ca/~physics/p261/projects/flywheel1/flywheel1.htm

        Stored energy = sum of kinetic energy of individual mass elements that comprise the flywheel
        Kinetic Energy = 1/2*I*w2 , where
        I = moment of inertia (ability of an obeject to resist changes in its rotational velocity)
        w = rotational velocity (rpm)
        I = k*M*R2  (M=mass; R=radius); k = inertial constant (depends on shape)
Inertial constants for different shapes:
        Wheel loaded at rim (bike tire); k = 1
        solid disk of uniform thickness; k = 1/2
        solid sphere; k = 2/5
        spherical shell; k = 2/3
        thin rectangular rod; k = 1/2

Use the above to calculate the energy stored in the flywheel.  (The formula looks a little different, but it is essentially energy = mass * velocity squared in a rotating form)

It took exactly that much energy to get the flywheel up to speed. (in reality, it took more than that, because of the losses in the system.)

Bottom line - there is no energy in a flywheel that you didn't put there.  And when you take energy out, it is no longer there.

[nightwynd]

Sorry 'bout the late reply here, havent' visited half baked ideas for a while

The formulae that you posted there Jake are the same ones that I've seen other places...that's the formula for how much energy is stored into the flywheel...but what I'm wondering is just how much energy it takes to KEEP a flywheel spinning at a current speed.

[Mac]

Well I'm rather late responding as well, but I just found this forum...

but what I'm wondering is just how much energy it takes to KEEP a flywheel spinning at a current speed.

Not much, providing the flywheel isn't attached to a load. Basically all that must be overcome is friction (this includes wind/bearing drag etc.). A body in motion tends to stay in motion...

However, you must realize that a rotating flywheel is much like a battery. It can only store energy which is supplied getting it up to speed (as mentioned above). Once you connect it to a load (no matter how tiny), a bit of the energy is lost on every revolution.

So... If even you have a machine that will power itself thru 99.99% of a revolution, it will draw the other .01% from the spinning flywheel and this energy must be replaced or the machine will eventually slow to a stop.

Now if you have a large power stroke such as a one-cylinder 4-cycle engine provides, a flywheel is a great way to store energy from the combustion. This stored energy is then expended as momentum to help the engine "coast" through the ensuing exhaust, intake and compression strokes - and also to help smooth out the engine's power output. But it doesn't create or multiply energy.

Cheers, Mac

[macelyne]

Hello Jake,

I think there is a mistake in your calculation:

w, angular velocity is not measured in rpm.

What I found is w=2*pi*f

f is the frequency.

Frequency of a wheel means, as i understood

revolution per second performed

and is measured in Hertz ( Period / revolution per second ).

A second thing:

the formula is E= ( 1/2 ) * I * w? ( not w2 )

[lltfdaniel1]

yeah, that would be more easy to under stand, then lets say , a magnet motor, and some mystical electric double flux, yeah, it you had a small wheel, it would spin up quickly,compared to a big wheel,

edit,

hey why not stick some permanent magnets to take load of the motor a bit, the flux will help push the fly wheel faster,

hehe.