# Flybrids, flywheel batteries, flywheel regen?



## Valk (Apr 13, 2011)

Been doing a bunch of reading around since i joined a few days ago and have taken ina bunch of knowledge in a short time. still a longggggg long way to doing a conversion, limited almost entirely by funds but can never have too much information when the time comes to actually buy shit.

I remember way back when i was young seeing a show on tv. Was called Beyond 2000 and they had an episode where they talked about flywheel battery powered electric car concepts.

I know thise technology has been developed for heavy industry, F1 ect, but I wonder if anyone has done a homebrew implimentation.

Seems like a no brainer when it comes to regenerative braking since oyu lose a lot of energy in the conversion process converting kinetic to electric to chemical, back to electric back to kinetic. 


the idea of keeping the energy stored kineticly sounds the most efficient but could that energy be used to launch the vehicle from a stop with fixed gearing or would a cvt be a requirement?
trying to think of how we could accomplish this without additional expensive transmissions. 
I was thinking of a one way gearing that would engage witha clutch when the brake pedal is depressed. the flywheel would spin up to its peak rpm in that gearing and the when the vehicle starts to slow down the one way gearing would prevent it from slowing the flywheel. 
in a stick car, you could just continue your standard gear down to come to a complete stop. 

seems like getting the most ideal rpm back into the flywheel would require a continuously variable gear ratio though. 

another idea is to build your flywheel storage like a sealed electric motor. the rotor is the flywheel and its sealed in a vacuum cylinder. when you apply brake pressure your electric motor goes into regen mode and instead of applying current to the battery subsystem, it goes into the flywheel storage and spins it up just like a standard motor. 

I know this exists but it doesnt seem so hard to accomplish for somone with some basic machine tool experience. 

while on the topic of exotic energy systems, why not a solar powered sterling generator when the car is parked? great a thermo solar panel in the cars roof to heat a working fluid that powers a sterling generator to charge up the batteries when your away. such a system could be very light.

other idea?


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## Woodsmith (Jun 5, 2008)

I looked into this as a thesis idea but was 'discouraged' from following it up.

That doesn't mean it's bad just not suited to the MSc I am on.

Have a look at the size of flywheel needed to store the amount of energy you want from it. Also the speed it needs to spin at.
Then think about the gyroscopic effects it may have on a vehicle in motion.

It can be done for the small amounts of energy for regen but even in F1 there weren't many using it. It can get overly complex by the time CVT, vacuum casing, magnetic bearings and so on has been taken into account.


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## ciggy (Mar 24, 2011)

As woodsmith has hinted the flywheel needs to spin at tremendous speed to have decent energy density. They need to be built out special materials and have perfect balance so they don't explode. (a housing that can contain the flying debris from a flywheel that desintigrates at high rpm is required for safety). Asking the rotor of an electric motor to do double duty as a flywheel would be quite an engineering task as the rotor of each machine already has many requirements and designing electric motors that work at super high speeds is more complicated than normal ones.

On the flybrid website you can see a glimpse of their second generation design using fixed gears and clutches instead of a cvt. The power lost in a slipping clutch is related to the speed difference between the input and output shafts. For this reason using only one gear and clutch to connect your flywheel to the driven wheels would probably have poor efficiency outside of a narrow rpm range.


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## Valk (Apr 13, 2011)

well i don't claim to understand the complex mathmatics and material science needed. though they are spinning their flywheel that weights like 25kilos at 60000 rpm and releasing the energy mechanically. spinning a 7 lb flywheel attached to a clutch at 1000 rpm is enough to make a average size car lurch forward quite a distance so im sure its workable with limited high tech resources.


why not a couple smaller, lighter flywheels made up of perminent magnet rods only a a few inches in diameter suspended in a vacuum vessel with magnetic bearings. instead of using mechanical means, you wrap windings around the outside of the chamber to spin up the magnet when braking, and then generate electricity when you start off. doesnt have to store energy for very long but this could be a lot lighter and less complex than a bank of super caps. id just be worried about having my regen go back into the battery cells cause wouldn't that go against their number of charge cycles?


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## jeremyjs (Sep 22, 2010)

Here's why flywheels aren't good at storing any meaningful amounts of power in automotive applications.

http://en.wikipedia.org/wiki/Flywheel

For a quick reference scroll down to the "Energy stored" section


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## ciggy (Mar 24, 2011)

Valk, 

it's not impossible or crazy, I don't mean to give that impression, it's just a question of practicality. If you want to build a flywheel purely out of interest in flywheels then don't let anyone stop you. If you want to build an electric car and are trying to find the best solution to power it run the numbers to see how much power can be stored in 7 pounds of batteries vs 7 pounds of a low speed home made flywheel. The energy stored isn't proportional to the rpm, it's proporptional to the square of the rpm. That makes high rpm essential. I did a quick napkin calculation for a perfectly ideal 7 pound, half meter wide flywheel spinning at 1000rpm and got 346 joules of stored energy per kilogram of weight and that was being generous, ignoring any housing weight etc. Ultracaps are somewhere between 5,000 and 20,000 joules per kilogram and batteries are hundreds of thousands of joules per kilogram. How inefficient would your kinetic->electric->kinetic conversion have to be before say 20,000 joules per kilogram was reduced below your 346 joule flywheel with a perfectly efficient cvt? I get 1.7% as the breakpoint. If you do better than 1.7% conversion efficiency seven pounds of caps is better than 7 pounds of 1000rpm flywheel. By all means run the numbers yourself to double check what I got but there's definitely a reason commercial flywheels run up around 20,000 rpm to get energy density comparable to batteries. The flybrid unit runs even higher at 60,000 rpm.


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## dtbaker (Jan 5, 2008)

the idea of something spinning at 20,000rpm and potentially being in a crash that fragments it while spinning would scare the bejesus out of me.


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## Woodsmith (Jun 5, 2008)

The 'safer' way to distruct a flywheel is to use a woven fibre (kevlar, carbon, aramids) wheel inside a strong case.

When the flywheel distructs the fibres start to creap allowing the flywheel to suddenly expand against the sides of the casing that then slows it down and constrains the wheel.

Cast flywheels distruct by breaking into large lumps of shrapnal that present a smaller contact area with the casing and are more likely to puncture it.

I don't think there is a backyard or garage 'DIY' way to make a useful flywheel storage unit that is safe.


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