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Flywheel Bicycle: KERS for pedal-pushers


August 16, 2011

Maxwell von Stein's Flywheel Bicycle stores the power that would otherwise be wasted in the braking process

Maxwell von Stein's Flywheel Bicycle stores the power that would otherwise be wasted in the braking process

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In order to help boost their range, many electric and hybrid cars employ regenerative technology where braking energy is stored in the battery instead of simply being wasted. This idea can also be applied to electric-assist bikes, but what about bicycles of the plain old human-powered variety? Isn't it a shame that after having built up some good momentum, you just have to write it all off once you stop? Maxwell von Stein, a student at New York City's Cooper Union for the Advancement of Science and Art, thought so. As his senior project, he recently rigged up a flywheel to an existing bicycle, in order to harness the energy that's lost during braking. That energy can then be used to boost the bike when needed.

The Flywheel Bicycle has a continuously variable transmission in the rear hub. This is linked to a 6.8 kilogram (15 lb) flywheel from a car engine mounted in the middle of the frame. When the cyclist wishes to slow down, such as when they're going down a hill or coming to a stop, they shift the transmission to maximize the flywheel-speed-to-bike-speed ratio. This "charges" the flywheel with kinetic energy - effectively a mechanical version of what happens in an EV where a battery stores the scavenged energy.

Once they want to accelerate or climb a hill, they do the opposite - they shift the transmission to minimize the ratio. This lets the energy stored in the flywheel drive the transmission, giving the bike and its rider a boost. In a ride where speeds vary between 20 and 24 kph (12.4 to 14.9 mph), the system is claimed to not only increase acceleration, but to also produce 10 percent in energy savings.

Although the added weight of the flywheel would certainly need to be taken into account, the concept behind the Flywheel Bicycle is still definitely intriguing ... enough so that it won von Stein the Nicholas Stefano Prize, which Cooper Union awards to outstanding mechanical engineering senior projects.

Maxwell explains and demonstrates his invention below:

Source: Scientific American

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

Nice idea, BUT : not only the added weight is a no-no, but the biker will find out that the flywheel makes the bike simply dangerous when cornering, as the centrifugal forces of the spinning wheel will try to keep it going in the same direction.

As any science student who studied his textbook would have known in advance...


I just love the idea of an extra 15lbs to lug around when I am off the bike. Also the idea of a large spinning chunk of metal near an intimate area makes me nervous if there is an accident.!


Can\'t believe that won an award- there have thousands of flywheel projects. Nice idea but nothing amazing.


A good idea, but why not a concentric (to the rear wheel) flywheel? THAT would store some energy...

Edgar Castelo

The article makes no mention of the gyroscopic effects associated with flywheels. This effect generates a force at 90 degrees from the force applied to turn the axis of the flywheel, i.e. when you try to take a turn on the bike, the flywheel will attempt to lay the bike on its side (especially with the flywheel being so high up in relation to the center of gravity). This effect is one of the reasons why the \"inefficient\" chain drive in motorcycles has not been replaced by a drive shaft. BMW has made some drive shaft motorbikes, but it uses two, counter-rotating shafts that nullify the gyro effect.


As usual a lot of negative comments from armchair critics never mind the lad has a working concept which he obviously hasn\'t crashed yet. The gyro reaction effect takes place at the pivot point of the flywheel and this does not happen with the bike just as it doesn\'t happen with a motorcycles much higher revving engine flywheel mass. To get the gyro effect you would have to lift the bike off the surface and pivot it along the center line of the flywheel where it would try to resist. johnsh54 thinks this is what affects shaft drive motorcycles..NOT TRUE ..a shaft drive motorcycle is affected by torque reaction with the frame mounted engine trying to tilt the bike in the opposite direction of the resistance created from driving the rear wheel. Absolutely nothing to do with gyroscopic effect. If anyone doesn\'t understand this I could go on and on like the Duracell bunny.


Very cool stuff more power to HPv,s

Michael Miller

Its a nice basic idea and the gyroscopic effects of a 15lb fly wheel will not be a big factor until much higher rpm is achieved. What he needs is better control of the CVT to slow and accelerate the bike.

I\'d like to see the losses associated with a l-ion battery pack spinning the flywheel and translating that energy through the CVT to the back wheel. A 10% to 50% energy assist for a 200lb package (rider included) could be meaningful.


johnsh54, you\'ve got a good start, but you misunderstand a few things. 1. When you initiate a turn on a bike, you lean the bike in the direction of the turn, and the lean produces the rotation about the vertical axis. That lean would cause the flywheel to tend to rotate the bike in the same direction. 2. The height of the flywheel has no effect on precession. 3. The balance shafts on engines have nothing to do with gyroscopic effects; they counter second order engine vibration caused by unbalanced crankshaft and connecting rod masses. 4. A properly adjusted and lubricated chain can be 98% efficient. 5. Chain drives still persist on motorcycles not because of any gyroscopic effects of a shaft drive (which are miniscule), but because they are cheaper to make, and the drive ratio can be easily changed, something which is very important in any kind of racing. In fact, chains have been almost completely replaced on cruiser and touring motorcycles by shafts or belts which require essentially no maintenance.


Judging from the video, apparently the gyroscopic effect was not a big deal in this application. I am interested in the transmission as I do have an application where both the energy storage and the gyroscopic effect are desirable. If you have info on the transmission please contact me at jsrldesignllc@ntelos.net



That flywheel-in-motion definitely needs a cover or the bike will become known as the Neuter-Mobile.

Azar Attura

Here\'s a better idea, keep the \'electric transmission\' fueled by a typical bike battery, and run the pedals (chain mechanism) to spin an alternator that charges the battery! This way, the rider still pedals, but without the added strain, and the battery can be kept charged longer, in-turn extending the distance of the electric bike!

I have yet to see an electric bike like this!

Max Mad

This is pretty out there stuff- the fly wheel would work great for e-bikes- i would love to have one to check it out and maybe sell them.


There\'s some mis-information in the comments. Firstly while there is a gyroscopic force I bet it\'s insignificant and easily overcome by the rider. The wheels have a gyroscopic force too but you don\'t even notice it. Yeah I know they\'re lighter but the diameter is much bigger and that amplifies the force. Secondly, motorcycles with drive shafts don\'t have a gyroscopic issue they have a simple anti-torque issue. The motorcycle leans in the opposite direction to the driveshaft rotation as a pure reaction to the torque, nothing to do with gyroscopic forces. But the idea of having an open, spinning wheel so close to your legs occurred to me too. A finished design should lower the flywheel and enclose it. And the energy recovery system should be automatic I suspect to have a wider appeal to the public.


I am impressed that several commenters here made such polite and cogent corrections to the apparently incorrect presumption about gyroscopic effects. dgate, Drifter2 and warren52nz, you rock. Who knew we had such informed people around? It certainly doesn\'t show up in public policy discussions. When the Tea Party takes over, you three are going to be sent for re-education.

No, I mean de-education. Where do you get off knowing such stuff? It\'s un-American. Or, well, maybe those three are from Somewhere Else. The Antipodes?


I am wondering if the flywheel can be somehow located right next to the wheel sprocket.

Paul Anthony

The gyroscopic force (precession) is not insignificant. But to offer constructive comments this can be minimised by putting the flywheel down closer to the road. And dumping mass from the flywheel and making it\'s radius variable under centrifugal force - just like an old steam speed governor. This will make it\'s precession smaller at lower speed.

But whoever suggested electrical regen is correct - it is more efficient and cheaper to make with off the shelf parts now.


What it needs is a system where squeezing the brake levers shifts the CVT to put energy into the flywheel until the bike is nearly stopped, then apply the brakes and disconnect the flywheel so it can spin freely.

Then when the brakes are released and the pedal crank turned, reconnect the flywheel and automatically shift the CVT ratio as energy is drawn from the flywheel.

There\'s no danger of that flywheel coming apart. Gasoline engines spin in the thousands of RPM. This bike application would be running it at most a few hundred RPM.

What would make it more efficient is a flywheel with more of its mass concentrated near the rim.

Gregg Eshelman

I highly doubt electric regeneration is remotely close to the efficiency of a flywheel. The best storage and retrieval are with flywheels or pneumatic systems. I think a pneumatic system is preferable because of the safety and losses from precession and drag from air resistance from the flywheel. The pneumatic method can also hold energy after you get off the bike. The gyro would wind down after a few minutes. The gyro might be better if used in the orientation of a top, then there will not be any losses from turning and it would provide resistance to tipping over. Of course, you have to find a safe place to put it...perhaps behind the back wheel and covered.

With the proposed electrical regeneration you have motors and batteries perhaps some electronics a capacitor or two...it is going to add up and it is not inherently efficient anyway. And the battery will wear out. I think pneumatic is about 20% more efficient. Flywheel is theoretically near 100% but in practice lots of drag, friction, and transmission inefficiencies. Unclear exactly how much you get back. But it probably is not too bad at low speeds with quick captured energy use.

A simplified electrical regeneration might be ok: motor/alternator and some capacitors and electronics...forget the lithium, or whatever batteries unless you intend to charge them from the wall but conceptually that would make it something different.

It would be interesting to have some sort of competition between colleges for the best bike energy storage and retrieval where the weight of the system is factored in. Just have a hill where the bikes start at the top, stop at the bottom and then go up a second hill. The bike that goes the highest wins. They have to start with the same frames tires etc. basically they have to keep everything stock unless it clearly has to be replaced by something very different integral to the method employed. Batteries can be used but the level of charge must be precisely accounted for and cannot discharge to a lower level than where it was when it started. Added weight limited to 35 lb. The hills should be fairly ordinary rather than immense to reflect ordinary use.


Mindbreaker, Max Mad is not referring to regenerative braking, which exists on quite a few e-bikes but is acknowledged to recover only a small fraction of braking force, but rather to using a pedal-driven generator to power an electric drivetrain. Small generators and motors are quite inefficient, so his idea is doomed to fail, with generator losses on top of motor losses.


Since weight is the downside of batteries and a flywheel, why not combine them? You could stack the batteries in a flywheel frame to make better use of their mass.


Nice. I think it would be more appropriate at a different scale- the 4-6 seater commuter bikebuss, with the orientation as noted above, a vertical axis of rotation (requiring added gears to build)rather that a horizontal one (easier mechanically to build) another idea from motorcycle history is two counter rotating wheels to negate stray torque effects...Vincent HRD did this in the 50\'s, Ariel did this then too!

MadMax, were you thinking of disconnecting the pedals from the wheel? Were you thinking that they run the generator and the generator runs the wheels? I have considered this option and again find a great place for it. I have some patent issues to pursue here...details withheld for the moment.

Talk to motorcyclers...some dislike shaft drive because the shafts twist up then engage the wheel and a reverse occurs on deceleration where its much like the phenom we experience with car manuals and lurching, which is so tough on universals and punkins, a phenom like the new driver who misatches gear/pedal and ground speed and the car jumps slows jumps slows, dies...

Chieftan- thanks for the brilliant question. Lemons (weight) to lemonaide (flywheel)!!! \'call me up\' if you have more of these! seriously!!

Walt Stawicki Low Kinetic Hum,an Hybrid llc

Walt Stawicki

here is the real problem


going down hill doesn;t \'waste\' anything, you get momentum that you can use going up the next hill - even without a flywheel

the only wasted energy comes from friction either brakes or the air

in other words, it doesn;t do anything to pedal along a flat road \'storing\' energy in the flywheel

only when you might use brakes to slow down, can this thing store anything

even so it;s inefficient, as well as heavy

come on mr flywheel, i will race you and your 50 lb bike



Nice idea. Flywheels are easy it\'s the implementation that is hard, and this students has figured that out. This is a prototype on an existing frame, so a better implementation with a custom frame would not be difficult. Keep in mind the mass of the bike is not that important compared to the kinetic energy of its parts, or rotating mass (weight of wheels, tires, chain, etc.). This changes the kinetic energy from a problem for riders to a solution.


this defeats the purpose of riding a bike. just pedal. get some exercise.


Simple and easy to convert existing bikes (as a for sale kit),a battery recharging version would also be very marketable for electric power pack bikes,a fly wheel mesh guard or solar panel covered carbon fiber guard would be easy to retrofit.(for battery charging and quality LED/halogen bike lights. Good work.....!

Mike Thompson

Re Yakov -

The purpose of riding a bike is to get were you are going faster, and more efficiently than walking.


Wheee! my 2 cents. This needs to be put in a velomobile. You know one of those 2-3wheel pedal powered vehicles that are enclosed. They are designed for going back and forth to work with lights and turn signals. This would be useful if it helped from stoplights small hills and what not to make the ride to work more even. If its a 3-wheeler there is no real tilting and gyroscopic effect will probably be less noticeable.


Nothing new to me; I did the same thing back in 1973. Daimler did it with his first car back in the 1890s. I think it could be a great idea for a velomobile especially an electric one. Actually, a number of early motorbikes had this same feature. Must be nice winning a prize for inventing something that's been around for more than a 100 years. In fact, I'd not be surprised if Da Vinci didn't think of it as well.

rawly old

I always thought a compressed air version would make more sense. Anyone got any thoughts on that?

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