flywheel bike

[Ivan]

Thinking aloud about Ken's bike/trike requirements:

If you keep your motor  below 180W, and have the movement of the bike engaged by pedal assistance, you should find it's exempt from road tax/insurance/mot etc.

The main problem with this is that 180W doesn't give you much power for acceleration, top speed, going up hills and so on. Here's a suggestion: you turn on the bike, and the motor runs immediately. The motor spins up a large flywheel, thus storing kinetic energy. Flywheel is connected to the wheels via a clutch and gearing - perhaps CVT? This gives a short term power boost - say 5minutes worth of acceleration or hill-climbing.

Any comments?

[martin]

steering could be fun! - it'd be a giro too!

[Ivan]

I've figured that one out too - if the flywheel is lying horizontally - eg underneath the storage unit of a trike, then it will be able to turn easily, but will have mind-defying road-handling!

[northern installer]

Nice idea,but what about the weight of the flywheel?

[Ivan]

I agree, weight is an issue, but flywheel energy is defined by err, 'angular momentum' (starting to falter - been 100 years since I studied this!). The further out the weight is on the flywheel the less heavy it has to be for a given energy. Also, floating on magnetic bearings and housing in a vacuum will reduce frictional losses, allowing it to store energy more efficiently, and allowing it to be spun up to greater speeds.

Anyone care to do some calculations? What amount of energy are we looking to store? Let's assume we want 3-5minutes of power from the flywheel. What power are we looking for? 800W?

[guydewdney]

twin, contra rotating flywheels will help...

[Ivan]

Even cleverer - and we can then mount them in the vertical plane which might be easier for vari-belt driver power transfer.

[northern installer]

How about a very small flywheel running at ENORMOUS rpm,a bit like the push and go toys? the smaller flywheel would reduce the(very real)effects of precession on navigation,and the whole unit could fit in a small space 

[mespilus]

Is this flywheel spoked?

I rememeber a few years back the Italian Pursuit team were disqualified for having spherical weights on their spokes
which acted as incremental flywheels.

The faster the cyclist the longer the weights stayed at the rim throughout each wheel revolution.

[Ivan]

I've found an online calculator - http://www.wa4dsy.net/robot/ring-flywheel-calc

Let's assume we are looking for storage of energy equivalent to 5minutes at 800W output - which should help us over small hills and accelerate away from traffic lights at respectable speed. That's 5/60 of an hour x 800W = 0.0666kWh (=240 000 Joules)

Using the calculator:

If we go for a 24" ring flywheel (22" inside diameter) of 5.11kg weight, spinning at 10 000rpm, we get 239681Joules.

So it's feasible and realistic.

I have a vision of a cyclist (pedal-power), arriving at a set of traffic lights, but whilst stationary, pedaling furiously, spinning up the flywheel. When the lights change to green, he releases the clutch and the bicycle accelerates from 0-30mph in a couple of seconds, leaving the combustion-engined vehicles for dead.

[KenB]

Ivan,

Find me a material that will survive 10,000rpm, 24" diameter without bursting??  Cast iron craps out at 1000rpm for this diameter - trawl the net for flywheel explosions if you need any visual convincing of the destructive nature of flywheels.

The gyroscopic forces would be astronomical.   What you need is a series of small flywheels shaped and sized like beancans, running at approx 100,000 rpm.

The Sandia Labs in New Mexico investigated these about 15 years ago, as an alternative energy storage to batteries for electric vehicles.


Ken

[guydewdney]

spin at that sort of rpm, and the losses become huge. However, I agree that 10K @ 20 odd inches is phenominal...

[northern installer]

There shouldnt be any losses in the flywheel itself,just in the bearings that support it;but the reduction gearing-now thats another matter!but all feasable,the bearings on a turbo charger survive huge rpm,and violent extremes of temperature,but have to remain free running to allow the turbine to start;
The flywheel would have to be automatically decoupled from the bicycle on overrun,or the lollipop lady might get a nasty shock!   

[paul]

Petty to de-couple on overun as going down hill and breaking could 're-charge' the fly wheel.

[guydewdney]

The bushes (note) are phozzy bronze or similar, supported on a film of oil in turbos. They are balanced to within an inch of their life, and also tiny (relativly) and very very light (relativly) - they are designed to have the lowest possible rotating energy to reduce turbo lag.

You cant use this method with high RPM heavy things.

High speed heavy things - like grinders (for making precision cylinders) run on air bearings - the air has to run, before the thing spins. similar for magnetic.  Bit impractical for a 'bike 

Compressed air maybe as an energy storage? Light, simple, proven technology. There was a tread about an air car a bit back wasnt there? cylinder can be a sphere for extra lightness...

and fillable from a house (using a cheap 5 quid compressor...)....

Um?