What do you guys think of this KERS equipped bike?
https://www.youtube.com/watch?v=5FJcEvijjks
all comments and suggestions welcome...

the bike has a flywheel Kinetic Energy Recovery System as seen in formula 1 with the williams team. it stores energy that is otherwise wasted when braking by spinning the flywheel. the flywheels enrgy can the be transferred back to the rear wheel when needed.
The bike was able to travel a maximum of 21 meters using the flywheels power and completely unaided by the rider.

I don't get it- it propels the bike so slowly on its own, and if you were to use it as supplemental power, you'd be turning the flywheel too, slowing you down. Seems there's a clutch or differential missing in there somewhere.

I guess it's a start, but right now it's little more than a novelty.

Not to mention, I'm not exactly pumped at the thought of both the weight of a flywheel and all that weight moving that close to my future descendants. Maybe I'm alone on this, but I occasionally sit on the top tube while in motion to reposition and relax.

I could almost see the point on a city commuter bike where there are a lot of stops. Weight, complexity, and cost are the biggest negatives. Don't think the KERS system has any true benefits to it other than being an interesting student engineering project.

the idea behind it is that it can get you going again after you have stopped. it would only really be suited to cycling in a city where you would be stopping alot.

at the moment it does not provide much acceleration (can get you going to a speed of 5km/h), but as you said, it is a start...

after testing it and analysing the results we have realised that a lighter flywheel spinning faster would be more beneficial as the speed has more effect on the energy of the flywheel than the weight does.
at the moment it has a 15kg flywheel with approx 7.5:1 gear ratio from the rear wheel. this means that when you engage the flywheel at 30km/h, the bike will slow to 17km/h and the flywheel accelerates from 0 to 1000rpm. by increasing the gear ratio (therefore increasing the inertia of the flywheel) the bike will slow down more and the flywheel will spin faster storing more energy.

We have found that the bike can re-gain up to 12% of its initial kinetic energy.
With re-designing the flywheel we could increase this to perhaps 20% and it would be more worthwhile overall.

Thanks for the comments and yes, the spinning disc between my legs makes me nervous to!! safety bar in that area would also be part of future development.

A flywheel needs to have mass , bike people hate adding any.

The inertia of a flywheel depends on the shape of the flywheel and its mass. the energy stored is then = inertia x angular velocity^2.
as the velocity is squared it means that making adjustments to the speed has a greater effect than changing the mass...

So the development of the system would bring us down the road of reducing the mass to an acceptable level while changing the shape and increasing the flywheel speed to a maximum...

By doing the maths we figured that the flywheel weight could be reduced to 5kg and be capable of storing more energy just by changing the shape of the flywheel (having more material at the edge) and increasing the gear ratio.

Learning process!!!!

A flywheel can store so much energy. It is quiet limited, unless you spin it very very fast, then it might affect bike's handling (will be harder to lean). And you have to use it right away otherwise you loose it to friction. I guess it would be better to switch to an electrical system as Formula 1 did. That way you could add up all the energy from braking on a long descent and use it on the following ascend. But then it becomes an electric bike, so what's the point.

yes good point...
Finding the best combination of flywheel weight, shape and speed in order to store as much energy as possible is what we need to do. (obviously not going too far and exceeding what will function reliably)

The tests we carried out enabled us to determine which direction we need to go in!

We did consider the electrical KERS route, but opted for the mechanical flywheel type system because of its simplicity.

Very interesting to see something new in it's early development.

Solution in search of a problem ?

Perhaps...
The problem for us is that all the energy you build up when your cycling is lost when you apply the brakes... it would be worthwhile if just half of this energy could be re-uesd... so far we are at 12% and for sure the figure can be easily increased...

Maybe you could put the flywheel just aside of rear wheel (between wheel and frame, concentric with the rear wheel, supported by the frame) you could then put some kind of planetary gear system (planets on the hub face, sun gear fixed to frame) to run the flywheel faster than the rear wheel. Of course it would be much more diffucult to make but I think it would be more efficient and you could run a flywheel almost the size of the rear wheel. Just a crazy idea. Anyways good luck with your project.

The idea has been published great many times in various popular-scientific magazines since the early 80's (at least on my memory). Experimental implementations date back at least as much as well.

Any gyroscopic effects? If so, that might not always be convenient.

Current flywheel is what.......33 pounds??!!!!!

+1. Regenerative braking is available on some electric-assist systems: https://www.bionxinternational.com/bi...rofit-systems/

Yeah that's what I was wondering, that's A LOT of weight to carry up hills.

Gyroscopic effect was not great enough to effect the bike handling even when we had it spinning at 2000rpm.

Yes the flywheel is much too heavy at the moment...

Thanks for all the comments and suggestions. i will upload some photos of the build!!

What can you do about the part where you can't use the stored power to supplement pedaling right now? If it's engaged and you're pedaling, your pedals are spinning up the flywheel instead of the flywheel adding power to your pedal stroke.

Do I have it right that you can only really extract power from the flywheel when you're not pedaling?

you can extract the power from the flywheel when pedelling. it acts as a boost so long as the flywheel is spinning faster than the speed bicycle travelling at. if the flywheel spinning slower, you are actually wasting more energy to spin(charge) flywheel, therefore you disengage the clutch to avoid this.

I am interested in this idea for a long time. have you thought using a variable moment of inertia flywheel? it will be a lot lighter

I think it's quite a fun project!

I can also imagine it evolving into a bike people would like to own, perhaps; a 5kg flywheel plus drivetrain and fittings is still a significant amount of weight, but there are plenty of people who willfully ride 38kg bikes everyday.

Of course, most of those heavy bikes are comfort oriented and fully kitted-out, so maybe rendering your flywheel in a Dutch style fabbed in Alu would be the target.

Anyway, keep at it guys, and keep us up-to-date!

thanks for your comment...we want to gain more performance from the flywheel and want to reduce the weight of the flywheel. we were thinking of reducing the weight by making a rimmed flywheel, with a thicker outer radius. this alone could reduce the weight of flywheel by a half, while maintaining the same inertia value. the next idea is too increase the gear ratio further. by doubling the gear ratio we could reduce the weight by up to 4 times,
to further increase performance a second clutch with a one to one ratio to sent power back from the flywheel to wheel is also a future opportunity . what u think.