I’ve always wondered why kinetic energy (KE) can’t be stored using a finely wound leaf spring in the rear hub. To store KE, the rider would engage it when decelerating, which would assist braking and prolong the life of brake pads, and engage it again to release the stored KE when ascending a slope or bucking a headwind. Surely modern space-age composite materials exist that would make this feasible. Even an additional 10 lbs of tractive effort would make hilly terrain less formidable.
WAG to follow. I would think that any spring that would cause a noticeable difference in acceleration would just about flip you over the handlebars as soon as you engaged it. And any spring that was light enough that it didn’t do that, I get the feeling wouldn’t even be able to move the empty bike. Add to that the added weight of the mechanism and another thing to fail and I’m not sure it’s destined to happen any time soon.
Now that I’ve said all that, I’m sure someone will come along and post a link to a website that sells bikes that have this feature.
This guy here seems like he has a working prototype for a bicycle. I don’t have sound at this computer so I can’t tell for sure: http://www.youtube.com/watch?v=UHPrOloikVE&feature=related
My first snarky response is “momentum”, but I live at the top of a hill with many stops on the way down, so I know where you’re coming from.
The real trick is if the added weight will be worth the energy you save. Let me break out some basic physics. For the sake of making my back-of-the-envelope calculations a bit easier, let’s assume that the bike and rider weigh 100 kg together, and that we want to get some energy out of decelerating from 10 m/s (for the metric challenged, that’s 220 lbs and 22 mph).
The kinetic energy is .5 m * v^2 = .5 * 100 kg * 100 m^2/s^2 = 5000 J = 5 kJ
From a wikipedia chart of energy density,, springs can store about .3 kJ/kg, good capacitors around 20 kJ/kg, , flywheel at 500 kJ/kg, and lithium ion batteries at 720 kJ/kg. Those are the only vaguely realistic storage methods I see on that page…
At the bottom end, for the spring to store all of that energy, you’re talking about 17 kilos just in the springs. Capacitors would only weigh .25 kilos – entirely reasonable weight. Batteries would be a tinier fraction yet; just 7 grams. A single AA would store all you need. However, you wouldn’t be able to charge or discharge it fast enough to be of any use.
My money would be on the capacitors. You’d still need to add an electric motor, and some sort of transmission, which would give some more weight and mechanical resistance.
And, after doing all that, I googled to find this bike, that seems to be exactly what you’re talking about. This is using a largish battery to provide a decent amount of power, but I’d bet it could do even better with some odd combination of capacitor and batteries.
State-of-the-art battery technology already solves the problem you are adressing, i.e. slow KE storage and restitution.
Springs are definitely not the solution in this case. A pair of contra-rotating flywheels might be feasible, yet for real efficiency a fairly large diameter and high top speed of the wheels would be required, resulting in high inertia likely to seriously disturb the biker’s balance.
Hence, the first thing an inventor has to look for is a problem that has not yet been solved. Being myself an inventor, I’ve given some thought to the unsolved aspect of this problem, i.e. the quick KE storage and restitution.
How do you act when approaching a green traffic light? If you’re at high speed, you want to keep it high, hoping the light will not go red. Ideally you’d like to pull up at the last moment with maximum deceleration – if you make this a habit, you’ll soon get the exact feeling for this kind of last moment braking, i.e. for the distance as well as for the braking force.
Yet the problem with this is: when the light goes to green again, you’re stuck in high gear. So the problem you really would like to have solved is the storage of a lot of energy in a very short time during power braking, and then the ability to rocket away in high gear from still-stand with a maximum short-time yield of the stored energy.
The solution I’ve envisaged so far is indeed the leaf spring like the one in the barrels of watches, and the solution for the variable torque transmission from the wheel hub to the spring barrel hub and vice versa may well be found in ancient watches where this is done through a simple spiral groove pulley, with the spiral pitch matched to the spring’s torque curve.
The advantage of this solution is obvious: if the system is tuned to the total mass to be decelerated/accelerated (biker + bike), it can work without CVT (Continuously Variable Transmission).
The video provided by Dog80 is much of a pity: these youngsters (I’m 66) got the whole thing the other way wrong (versus yourself) – although they correctly adressed the restricted problem of rapid KE storage and restitution (since they choose the mechanical spring solution), they use an unnecessarily complicated system to solve the problem.
As to the specific problem of bucking a headwind, as you put it, this needs a constant energy assistance rate.
The solution would be a constant speed (variable pitch) wind turbine fixed to the bike frame and geared to the front wheel hub, preferably with a CVT in between. Not only will the propeller shield you from the wind and therefore reduce your body drag, but it will convert the potential energy available from the air moving relatively to the road surface, into additional drive force, whereby the yield of the system ought to increase with increasing road speed and/or road-air differential speed.
Not in this case. It was for an electronics competition, so the microcontroller and accelerometer were necessary.