Aero engineer really needs your help !!



Jago23

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Nov 19, 2007
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Hi, im an engineering student and have been asked to design an innovation product that resolves a problem. My group feel that we should redesign the bicycle light, using a dynamo like system as opposes battery power. Does anyone use dynamo systems for their bikes and if not, why not? Is the power source or cost of running a bicycle light really a problem? Any feed back would be much appreciated.. Thanks :D .
 

Yojimbo_

Well-Known Member
Apr 17, 2005
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I don't use a dynamo, although I did when I was a little kid (many many many years ago).

My memories of the dynamo are that it makes a lot of noise, and sucks a lot of energy out of the total available. I see from various searches on the web these days that there are different dynamo systems available and I presume they have been improved substantially; however, I see no need to get one.

The combination of LED and improved batteries is sufficient for my needs. Since I ride on the road in generally well lighted areas, a flashing strobe for the front and back is adequate. I recently bought a Dinotte front / rear combination, and while it certainly wasn't cheap, it is very bright and will last for much more than I need before recharging is necessary.
 

gclark8

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Apr 13, 2004
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NO DYNAMOS!

Research solar charging of suitable existing bike batteries.
Develop a paint surface that will charge a battery. ;)
 

artemidorus

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Mar 10, 2004
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A number of expensive European hub dynamo systems already exist, in addition to the power-sucking tyre-rolling horrors of our childhoods. Those childhood recollections will poison the dynamo market for some time.
 

scirocco

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Feb 16, 2007
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artemidorus said:
A number of expensive European hub dynamo systems already exist, in addition to the power-sucking tyre-rolling horrors of our childhoods. Those childhood recollections will poison the dynamo market for some time.
Ain't that the truth. Those things were horrible. The hub dynamos are pretty good, though.

Solar electricity generation is very inefficient and expensive, and would need a lot more surface area than the frame of the bike - think panels on the roof of wherever you keep the bike. Quite apart from the obvious fact that it doesn't work well at night, in the early morning or late afternoon or in gloomy winter conditions which is just when you need it most, so you would still need to lug heavy batteries around.
 

Phill P

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Jul 9, 2006
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Design an aero dynamic rear bike "pod" that mounts onto standard rear rack but works like fairing rather than an air brake.

I would expect the only people using dynomos are people who do extensive night riding and don't want to replace batteries every other day. Mountain bikers mount big water bottle batteries that they recharge when they finish riding.

I saw a guy upgrading his dynomo in his touring bike. The hub itself housed the generator with the quick release operating as one of the terminals. Very slick, very aerodynamic!
 

daveryanwyoming

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Oct 3, 2006
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Jago23 said:
Hi, im an engineering student and have been asked to design an innovation product that resolves a problem. My group feel that we should redesign the bicycle light, using a dynamo like system as opposes battery power. Does anyone use dynamo systems for their bikes and if not, why not? Is the power source or cost of running a bicycle light really a problem? Any feed back would be much appreciated.. Thanks :D .
Come on, you can do better than that. How about a continuous bicycle transmission set up in a closed feedback loop with a power measuring hub. That way you could train constant ergometer like intervals on your road bike across a certain range of grades, preset power levels and wind conditions. Start with some sort of conical hub based continuous transmission, or maybe a drive by wire electronic transmission, hack the serial protocol from a used PT pro hub, develop the feedback and shifting algorithms and prototype the thing.

Jeeze, I sure wouldn't have gotten through engineering school on a rim mounted bicycle light generator. :)

Good luck,
Dave
P.S. Forget the erg-bike. I see your an aeronautics engineer, how about taking a portable weather station, gps unit(differential gps would be better) and power meter. Figuring a way to synchronize or time stamp the data from each and create a field CdA testing kit. Collect, speed, power, road grade, direction of travel, wind speed and direction, barometric pressure and dew point and you have enough info to do CdA regression testing that will yield both CdA for different yaw angles relative to the wind direction and tire rolling resistance. Now that's a cool project for an aero engineer.....
 

mikesbytes

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Apr 12, 2006
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gclark8 said:
NO DYNAMOS!

Research solar charging of suitable existing bike batteries.
Develop a paint surface that will charge a battery. ;)
+1

Problem with dynamos is that the lights are not working when you are stationary.
 

Sikhandar

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Jul 5, 2007
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Expensive? The shimano dynamo hub costs about 40€...........and works perfectly. A friend of mine has trainings during nighttime thanks to it....
 

dabac

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Sep 16, 2003
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Jago23 said:
...Does anyone use dynamo systems for their bikes ..
Yes, on the beater. No maintenance, always ready for action, and on short runs the extra drag of the dyno isn't a concern.

Jago23 said:
...Does anyone use dynamo systems for their bikes and if not, why not?
Not on the commuter or the MTB. Not having a hub dyno I'm not about to put up with the extra drag for the commute, where speed is of considerable interest to me. Besides, parts of that route is so poorly lit that I doubt if any dyno could cope. Not on the MTB either, tech sections drops speed below what's required for good dyno action and lots of light needed.
Jago23 said:
...Is the ..cost of running a bicycle light really a problem?
Depends on what your requirements are. If you're riding well within your ability and only want to comply with legal requirements and perhaps have enough light for modest speeds, then cost is not much of an issue.
But if you're riding hard in the dark it becomes another question entirely. High performance systems comes at a significant cost, particularly if you want to keep the battery weight down.

Jago23 said:
...Is the power source ...really a problem?

Depends on what your requirements are. If you're riding well within your ability and only want to comply with legal requirements and perhaps have enough light for modest speeds, then even a crude bottle dynamo would be sufficient. Disposable batteries can also last long enough to be a working solution if your requirements are simple enough.

But if you're riding hard and fast when it's dark and cold it becomes another question entirely. At a 2nd thought, slow and hard can be equally difficult.
Steep climbs and difficult trail passages can drop your speed to the point where dynos don't work very well, your tires can pick up sleet/mud which causes bottle dynos to slip ASO.

Hub dynos have gotten a good rep, but if you didn't know you wanted one when you got your bike they will require a wheel rebuild or a new wheel. And maybe you want something more from your hub (holes, brakes axles...) than the hub dynos can offer?

Rechargeable systems needs to be recharged, which might be an issue if you're into unsupported touring, or if you regularly store the bike at different locations. If you're commuting you might need a charger at each end, or carry it with you on every ride.

Then there's the question about how you like your bike, some people will be happy with a rather permanent light setup on their bikes, others will prefer something that can be easily removed on "race day" or simply when it isn't needed. Some will insist on easy removal to keep the bits from getting removed by someone else...

What I'd like to see (more of) are small and neat bike powered lights that are sufficient to comply with legal regulations. These can be left on the bike permanently, and then I can attach/remove the riding lights as I see fit.

One idea that I find tempting is to see if a piezo crystal in the seat post could generate enough energy to power a rear led blinky for instance.
 

threaded

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Jul 6, 2006
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A good dynamo hub will generate 3w. Yet I find a 5w light to be the absolute minimum...

So if a hub dynamo were to generate enough power for the lights it would cause too much drag in making that power. :rolleyes:

Not good.

How about looking at a miniature magnetic wheel bearings. :D
 

bobbyOCR

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Aug 31, 2005
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I got a 6W LED system that weighs less than 150g complete and has enough power to race offroad at night. I'll stick to them.

I'd rather see the GPS too.
 

artemidorus

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Mar 10, 2004
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Sikhandar said:
Expensive? The shimano dynamo hub costs about 40€...........and works perfectly. A friend of mine has trainings during nighttime thanks to it....
I didn't know about that. Well, Jago, there's no way you're going to beat that, at that price, in a hurry.
 

artemidorus

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Mar 10, 2004
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How about a braking system that generates power to extend the burn time of a rechargeable lighting system? You could run that on the rear wheel and keep a normal brake on the front wheel for hard braking. I suspect that it wouldn't do much, however, given that one is only braking for a small fraction of the ride time.