# COMMUNITY : FORUMS : TECH

## Carbon Fibre Flywheel (for energy storage)

I'd like to build a flywheel but I'm not sure what I need to know before i start, Is it difficult to do? Is it possible to accomplish with off the shelf parts? Any help at all would be appreciated greatly.

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ilovelemons9 years ago
So, a question. Most of what I've seen on flywheels concentrates to a significant degree on energy density and issues related to mobility. How about if I want to go the other direction? If I have a wind/solar energy source and am looking for a storage sink - how about a big, fat, slow - but massive flywheel? I kind of like the idea of 100 tons of concrete cylinder moving at about 30 RPM to provide temporary storage. I've got a big yard. I know I'm not going to like the answer - but could someone point me to the right equations for determining the energy storage capacity of a rotating cylinder of mass 'x'? Thanks
1 year ago

Let me tell you about one of my concrete flywheel experiments.

500# of concrete and 3/16 steel rim to hold it together.

4'x6' hole in the back cement block wall of the garage.

totaled out a 3 month old Mercedes parked on the other side of the wall.

3 weeks in the hospital

6 broken bones

9 years ago
. That ought to work. It's the ?gyroscopic? effects that make moving it around so cumbersome. Not a problem when it sits in one place. And a huge, slow rotating flywheel is much safer. . Not sure about the calcs. I think angular momentum is involved. Try searching for that.
anybody154 years ago

G'day,
As others have pointed out energy storage goes up with the square
of the speed, so it is better to have a faster flywheel that weighs less.
To put numbers on it. If you have a 400kg flywheel ( yes I'm ignoring second moments defined by flywheel shape for now) doing 500rpm(51 rads/sec) you get about 1067kJ of stored energy if you take a 4kg flywheel and spin it at 5000rpm (517 rads/sec)you get the same amount of energy. at 10,000 4271kJ4 4x more, at 20 000 rpm 16x more. The problems of drag at high rpm and electrical losses of getting the enegry in and out aren't trivial, but it's (almost) always betters to sacrifice mass for rotational speed.
BTW Audi used a flywheel sucessfully at lemans this year to recoup braking enegry.
Stephen.
Kiteman9 years ago
As far as I know, no vehicle has ever been successful with a flywheel as its primary energy source. Certainly no car has, as a large-enough flywheel plus associated framework and gearing will not fit inside a car.

However

I have heard of trials with buses that use flywheels as intermittent energy stores - the breaking system transfers energy to the flywheel as the bus slows, then that energy is used to assist the bus pulling away from stops.

The wheel needs to have as much mass as possible, moving as fast as possible, as far from the axis as possible. Carbon fibre alone is just not massive enough (maybe you could bind a steel wheel in CF to restrain possible shrapnel?).
7 years ago
Although this car (www.time.com/time/magazine/article/0,9171,985185-2,00.html and money.cnn.com/magazines/fortune/fortune_archive/1996/09/30/217438/index.htm) doesn't use the flywheel as the "primary" power source, it takes care of the power demand for acceleration.  I remember seeing a television documentary about the Rosen Motor Company that both articles treat in depth.  In contrast to the failed test that the article mentions, the television program highlighted a successful test of the Rosen Motor power train, installed in a modified Saturn sedan, which used the flywheel storage and a turbo generator for the electricity.

Again the flywheel is never going to be the "primary" power source in anything, but its ability to "buffer" power and even out the demand curve will make flywheel energy storage systems (FESS: my acronym?) almost "primary" in their ability to reduce or "even out" fuel consumption.

I've also read that mobile applications of FESS can use a gimbal arrangment to "unlock" or free the flywheel's angular momentum/velocity from being "tied" to the vehicle's angular momentum/inertia when negotiating all those pesky curves in the road.
H2SO47 years ago

The rotational kinetic energy of a hollow cylinder =                                           Energy rotational =1/2 M ( r_1^2 +r_2^2 ) * V_a^2

Where M= mass of cylinder   r_1= inner radius r_2= outer radius and V_a= Angular velocity in radians/sec ........... This equation states that rotational energy increases with the square of the angular velocity. Which is why commercial high energy density flywheels have insane rpm rates, more energy for a given system mass. However, as has already been stated, when these units fail, they dont just stop working, they explode!!! I have heard of carbon fiber flywheel failures that resulted in a pile of red hot ash at the bottom of the chamber. That does not sound like something that I want in my car...

7 years ago
He's been gone for >2 years, but the maths is a good addition.
You were thinking of those flywheel-toy-cars like I was? (vrrrrrroooommmmm....)

L
LasVegas9 years ago
I don't know how you could do it right with off the shelf parts. The flywheel would have to be perfectly balanced with bearings that produce near zero friction. Transferring the power to and from the flywheel would be another mater altogether.
nuncoop (author)  LasVegas9 years ago
I'm thinking about using rare-earth magnets, or some kind of electromagnetic set-up (preferably the former). The only thing I'm not sure about is how to make a flawless carbon-fibre flywheel, or if I should just resort to buying one directly from a manufacturer.
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