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I propose a regerative brake for a bicycle. Why waste the perfectly good forward momentum that you had before had to stop at that bloody red light? Where I live, the city seems to have timed all of the lights to stop all slower moving vehicles at every light. I quite enjoy cruising along, but I hate
having to stop and start all of the time.
There would be a spring or something mounted on (or in) the frame of the bike that is hooked into the rear brake lever and the gears of the bike. When you apply the brake, it winds up the spring and when you release the brake, the spring releases its energy thus accelerating you to your previous velocity.
You could also do a high tech version with an electric motor and flywheel a or battery.
(?) Spring regen patent
http://patft.uspto....577&RS=PN/4,744,577
This was 16 years ago, I wonder if anyone has tried it since? [shameless_self_reference, Sep 20 2002, last modified Oct 04 2004]
Air Powered Bike
http://www.instruct...E5OMNXCU2REP2860RS/
Some guys actually tried out air power for thier bike, although without regeneration [James Newton, Jun 15 2006, last modified Aug 27 2007]
Energy Densities
http://en.wikipedia...storage_and_in_fuel
[FlyingToaster, Mar 06 2010]
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If you use a spring, the brake will need to reverse the direction of the spring action after winding, otherwise you end up going very fast, backwards. Seems relatively simple to do, though, with some sort of iterant transmission gearing. |
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I remember reading about some city buses that used a pump to compress hydraulic fluid in to a nitrogen filled tank as part of the braking process and then reclaimed the stored energy by way of a hydraulic motor which assisted the engine of the bus as the bus got under way again. The pump and hydraulic motor may have been a single unit, I don't recall the particulars of that part. |
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Electric idea is baked I think. Sinclair Zike. General problem I think with regen using batteries as storage is that although the energy density is good, the rate at which you can get that energy in is limited. |
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Howabout a caliper with friction wheel pressed against rear wheel balanced by idler on opposite side, first half of rear brake lever engages friction wheel on rim, friction wheel transmits power though helical steel cable (like car speedo cable, or those bendy things with a drill chuck at the end?) to the spring, could be large "constant force" style strip spring like in car seatbelt. A little thumb control engages a clutch between cable and spring when you need extra power. Maybe you can do away with the cable and mount the spring on the back wheel on the caliper. |
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Energy = 5000J for 100kg bike+rider from 20mph. I make that 1kg of steel if uniformly stressed at 1400Mpa, might only get half that in a practical spring, so maybe 3kg for complete assembly inc controls, caliper. Might be bearable. |
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Rubber is 3000J/kg at 100% strain but a rubber band stressed like that wouldn't last many cycles. |
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This is bakeable I think, so croissant! |
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[half] You are right, there are some hydraulic regen systems around, but system is only practical at much higher powers and energies than a push-bike. Power density of hydraulic machines is second to none. Accumulators are a good way to store energy for regen braking as peak power is almost unlimited and energy storage is not too bad. I happen to be working on a new electrohydraulic technology which will be an enabler for such systems.
Problem with conventional hydraulic pumps and motors is efficiency, especially at part load. Our technology is highly efficient at part load, has very high response speed and is computer controlled.
I built a little golf car with hydraulic regen braking last year as a demonstrator for one of our industrial partners, and it is now exciting interest from teir one automotive suppliers. Watch this space! |
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With a fuel cell bike, braking should be able to generate power to run the fuel cell backwards, using some of the water to replenish some of the hydrogen. |
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For this sort of small-scale application, I'm sure pneumatics would provide a much better power-to-weight ratio. |
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1. The working fluid is freely available. |
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2. You can build air motors easily from aluminium alloys, industrial plastics, and ceramics. They're lightweight and long-lived. |
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3. You could use the actual bicycle frame as the pressure reservoir. |
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I'm not sure if air motors are reversible to make them into compressors, and you might have to change the gearing between modes (could be done with a CVT) but this idea shows promise. Croissant. |
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Fuel cells are an interesting idea. I was also thinking of a pneumatic system that works in a similar way to those hydraulic systems that the big trucks use. You could then also charge it up at home to give you that boost whenever you need it. The pneumatic motor could also double as a compressor. As with all bycicle add-ons this device couldn't weigh much over 2 Kg, how light could you make an hydraulic system? |
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Even if you use a low molecular weight hydraulic oil like Skydrol, there's going to be a fair bit of mass involved. And the hydraulic system doesn't store energy, it's just an intermediate power transmission system. You still need the pressure tank, and the fluid reservoir - so, together, pretty bulky and probably heavy too, even in alloy. Let's hope [s_s_r] will crunch the numbers for us. I still favour the direct-acting pneumatic system. The idea of precharging is good, you could even have pyrotechnic gas generators to get you up long steep hills. |
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If you've got decent, compact fuel cells, you might just as well have an all electric bike you don't have to pedal at all. |
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You can forget hydraulics for push bikes. The powers and energies are too low for the advantages to win over the disadvantages. High pressure hydraulic machines of the 100W scale are too tiny to make accurately, so they leak, so they are innefficient. And yes the energy has to be stored as compressed gas anyway. |
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Hydraulic accumulators achieve high energy density by storing gas at 100's of bar. Pneumatic machines cannot work at these sort of pressures because air has such low viscosity and is so compressible. Standard pnemuatics working pressure is 10 bar. To store 5000J, your pneumatic tank volume is about 10 litres. Though it will be light, maybe 2kg? (low pressure = thin walls), that's a lot of bulk. A high pressure gas accumulator would only be 500cc or so, although it would weigh about the same as the pneumatic tank. But then you need to carry an extra 500cc of oil in a low pressure tank. Messy. |
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Why is nobody keen on the spring idea? Springs have high peak power, do not leak, do not run down, offer good energy density and specific energy, are cheap, give back almost all the energy you put in, and are unlikely to explode. |
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Lest any of you be worried about the safety implications: Hydraulic accumulators have been compared to unexploded bombs. That is unfair and innacurate. They are more like bombs which have *already* exploded, but have yet to undergo case fragmentation. |
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Bicyclists who don't have enough mountains on their regular route - something I heard someone complain about yesterday - could create the impression of mountains by storing and releasing brake energy. |
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That is another exciting use for it, a mountain bike without the mountains. I do think that the spring idea will be the easiest to implement. However, it would be so much more satisfying to hear a pneumatic hiss coming from my bike and be incredibly cool if the motor sounded just like one of those pneumatic drills that mechanics use to tighten lug nuts. |
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Regenerative braking could be done by driving an air compressor that increases the tire pressure then bleed them off to a turbine (same compressor) to get an assisted start. |
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s_s_R: // Why is nobody keen on the spring idea? Springs ...... are unlikely to explode // |
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Precisely. We think you'll find that most HBers are enamoured of things that explode, or have the potential to explode. |
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// Hydraulic accumulators have been compared to unexploded bombs. That is unfair and innacurate..... // |
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I've got this eerie feeling that we may have worked together at some time in the past ............. |
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So if spring-based regen braking is so good, why has no-one done it ? |
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I know nothing of how to engineer this; I do know the stopping-starting problem with timed red lights; I am guilty of sometimes diverting to the pavement when there is no point sitting in the traffic with every other sucker's exhaust fumes just because there isn't a cycle lane (I *don't* divert to the pavement just to take advantage of the pedestrian crossing when the traffic lights are red).
I think this is truly halfbaked, and thus worthy of a croissant, yet not viable for baking, because the problem is not really desperate - unless you are going really really fast, there is not a lot of momentum lost by stopping for some traffic lights. Given all the other things for which you have to slow down, inclines which decrease your speed a bit, and the fact that cycling is all about putting some effort into your journey, it strikes me as somewhat lazy to put a complicated/expensive hydraulic system into your bike so that you don't have to expend any more effort in getting up to your previous speed. I may be wrong, and I don't live in the hilliest place in the world, but my 'take' on this idea is that it's cute, but no thanks. |
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I picture cyclists eyeing each others' bikes up while
waiting at the traffic lights to see who has the biggest
spring, and then wheelspinning away as the lights turn
amber... |
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My father was hired by a man who had raised a lot of investment capital to build a spring powered car. My dad worked as a clock maker and built a model as a "proof of concept." As time eventually told, the problem was one of weight to power storage capacity. Any spring able to store enough energy to be useful, weighed more than the car could carry and / or was so tightly wound that any accidental release of the energy would have been deadly. Now... they did not have carbon fiber or other modern materials, but they did try everything that was commonly available in the 1970's. Also, they found that the idea worked better as the vehical got smaller, e.g. the little car my dad made was pretty good, but the big car was useless so maybe a bike would still have some value. |
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I like the pneumatic idea... except for the explosive potential. |
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How about if some part of the suspension was replaced with a spring that tightened up as you stopped and then released as you started? Imagine a low rider going up and down but the frame of the bicycle is flexing instead. It could also provide a nice, springy ride when underway. And since part of the frame is replaced, the weight increase might not be so bad. |
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You could have an extra, slightly smaller, back wheel on the left. To brake, you lean over to ride on the nonspinning left wheel that is forced to turn and through gears cause the right wheel to spin rapidly like a flywheel. When the light turns green, transfer your weight to the right wheel and peel off. |
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First, you can strip all the weight you like off your bike, but YOU are 85% of the total weight in the first place! |
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Rolling resistance is proportional to vehicle weight, so adding 3kg of spring would as an extra 3-4% (load is bike PLUS rider) so not too much. If you are Chris Boardman and cycle all day at high speed the regen system is of no use, but will cost you an extra 2% energy (the other main loss is aerodynamic, and aero drag would be almost unaffected) |
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In start/stop traffic in town (cycle courier?) I guess 40-50% of your total energy input ends up heating up your brakes.
Say you get only 70% round trip efficiency from your spring system. IF its capacitiy is big enough to capture most of the braking energy over the duty cycle, you can reduce your total energy input by 25-30%(ish). |
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This is fine...on the flat. |
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Once you start adding steep hills into the picture it all gets less attractive. |
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If your duty cycle involves going up and down a 30 metre hill, with a freewheel descent which normally involves braking to limit speed, then your spring is going to be full after 10m or so, so a lot of that energy would have to be wasted by the brakes. But then most hills in most cities are not that steep that you need continuous braking, rolling and aero limit speed anyway.
So for a cycle courier in an averagly flat city, this idea still has some potential. |
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// So if spring-based regen braking is so good, why has no-ne done it ?// |
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If you are resorting to that old desperate chestnut, we just might be on to something! Well I must tell you, like any great weaver I always leave one tiny flaw in my designs.... |
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Perhaps this could be updated a bit... Power-assist bicycles now have motor controller electronics which regen energy back into the batteries... saves wear and tear on the brakes too. |
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On another note, I have an idea for a vehicle I call The Bow. Basically a recumbent tricycle that has a compound bow mounted under and behind the driver.
I hadn't thought about using fwd. motion to draw the bow. Rather, to pedal while at a standstill (eg at a light or at the bottom of a hill) to draw the bow, then "pop" a clutch when good to go... |
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buy a moped. (joke) Dudes and chicas, the brain flow here makes me proud. Still, inside my head, electric seems good....or a bad-A hybrid system (heavy, yes, expensive, yes) But, safe! and efficient! and cleanish! |
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PS: shimano is making an internal deraileur - essentially that madly cool self-contained bike transmission of yesteryear that dazzled |
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Missed this one the first time around. I like it. (WTAGIPBAN) |
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I had this idea too. And found this site. My idea was to use a pnumatic system.
Input: Pnumatic piston motor with regulator
Storage: Bike Frame
Output: Pnumatic piston motor fed wih regulation |
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It doesn't need to provide the full same acceleration as the rate of deceleration. It can provide an assistance for the rider to get off again. |
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It can also help in hilly areas:
Change the regulator and store part of the pressure, and release (blow off) the rest when going down a hill. Remember it may be fun going down a hill but it's in eficient and you still need to go back up. |
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I actually want to try this idea but I'm having trouble finding a pnumatic !piston! motor, it needs to be piston to be able to accumulate pressure. |
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What's more, if you go past a service station, you can pump up your tyres and your frame for power! You can also use an electic pump at home! |
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This idea has many advantages. |
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Going from 0 to 10 in 1 second or so might be dangerous. I recomend having a little bit of forwards motion when you start using the spring so you don't tip over early on.
( still be fun and would other people wonder ) |
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toad, did you try the air-compressor market? Perhaps a junkyard might have something like that. |
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Think of the extra weight you'd have to carry! |
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Using air as the working fluid would reduce the weight compared to a hydraulic system, but you'd still need very high pressures. As s_s_r says, trying to pump air at very high pressure is difficult because air is very compressible. Any ideas as to a way round this problem? A pneumatic system would not carry a large weight penalty as it would be empty when not in use rather than carrying a lot of hydraulic oil. |
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//While I am at it, does anybody know if there is such a thing as a variable resistance 36 volt generator that could regenerate power for an electric bicycle??//
Not variable resistance, but variable field.
Better to use permanent magnet (more efficient), and control current (and therefore the power required at the shaft) using electronics.
If you want a nice little motor or generator then look for "Maxon". They made the motors for the Mars vehicles, and they go up to about 90% efficiency! 400W only about 0.3kg. |
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I know this is very late to the conversation but this showed up on a search I was doing. Seems someone else thought it was a good idea too since there are a few current electric assist bikes with regenerative braking. |
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I see it as built with two modified brakes: one for pushing the wheel-to-spring transmission rubber rolls against the wheel, and one for locking the spring in place. With that, to minimize extra handles on the handbars, one could use some one-way-rotation-only device that would allow the spring to be wound up and unwound in the same direction using one axle only. That would involve some additional, perhaps ratchet-like, mechanism - but that's outside of this idea's scope. |
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With those, all that remains is to calculate the size of a steel spiral tape spring able to hold 15 kJ of potential energy without losing elasticity. I'd rather go with 15 kJ as opposed to just 5 kJ, as the kinetic energy of a 100 kg vehicle at 50 kph = 30 mph = 14 m/s is about 10 kJ and we'd rather work at a ~70% capacity, just in case. |
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Would a big capacitor work? |
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A battery is a big capacitor: just not a very efficient one. regen or dynamic braking is done by partially shorting the drive motor. if there's too much you go over the handlebarsover time this will de-magnetise the motors. brake blocks are cheaper. |
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A battery is a big capacitor: just not a very efficient one. regen or dynamic braking is done by partially shorting the drive motor. if there's too much you go over the handlebarsover time this will de-magnetise the motors. brake blocks are cheaper. |
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Search freepatents.com for similar ideas but be warned: That site is a bit frustrating if you think you had a great idea 'cause you are likely to find someone already filed a patent for it. |
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With regenerative breaking I especially like the idea of having all wheel drive, assuming the front wheel is powered by the stored energy. |
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I came up with >80kJ (23Wh) but I'll grant that's a maximum scenario based on 150kg worth of rider/bike/cargo and a 50m hill. |
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<link: Wikipedia: Energy Densities> |
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No sweat for a laptop battery, storage-wise, but I don't think they'd be up to the power requirement (that's ~3hp for a minute). Capacitors look promising (10kg worth of regular capacitor or 1~2 kg worth of super/ultracapacitor) |
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Spring would be 30kg for the 85kJ scenario so that's out, but only 5kg for the 15kJ scenario. |
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I still like pneumatic, though a tank blowout while riding could knock the bike in an unwanted direction/speed. |
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The idea was proposed in 2002. |
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Its a great idea and simple too. (Not the electric
bike, just a spring for starting you off, which is the
hardest). |
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Wow, very old but so valid.
I had the same idea, using a garage door torsion spring (or part of it) around a shaft drive (+ home made mechanism). |
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Steel torsion spring is given for 5kJ/kg, so 1kg fits the 100kg@32km/h(20mph) case.
But a tandem (or cargo) at the bottom of a hill (200kg, 60km/h) would need 27.8kJ so 6kg of steel torsion spring. |
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The idea is pretty still alive, patent link is dead but you can find it with nowadays references searching for US4744577 |
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I wonder why no bike went on the market though.
Would love to see it coming to life. Smell like croissant to me. |
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Burnouts on a bicycle with all your hard earned effort, cool. |
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