h a l f b a k e r yPoint of hors d'oevre
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A typical bicycle wheel comprises a rim which is connected to the hub by several spokes under tension. There are usually about 30 spokes on a wheel; each spoke made of a metal rod.
I think it would be interesting to make a wheel with a large number (hundreds or thousands) of very thin spokes.
This
could be used to created interesting visual effects. For example, the spokes could be weaved in interesting 'maypole' patterns. alternatively, the spokes could be made of transparent material (e.g. fishing line) so that the hub appears to float in the rim.
Of course there are several disadvantages to this idea including: difficulty in adjusting the tension of the spokes, and increased (lateral) wind resistance.
If nothing else, this would visually demonstrate that spokes work under tension rather than compression (this is not immediately obvious with metal spokes).
Disc Wheels
http://cyclinginfo....ls-for-time-trials/
Wheels formed of a disc in tension. [eight_nine_tortoise, Mar 10 2009]
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Annotation:
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The pressure alone will make this work without weakening the rim. The strong plastic spokes are not primarily there to strenghten the rim. They are there because the thin metal ones break easily in collisions. |
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This idea is beautifull. It is indeed very hard to make, some kind of machine is needed to deal with the difficulty in adjusting the tension of the spokes. Nothing an engeneer can't design on a sunday afternoon. |
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Increased lateral wind resistance is not a problem. I actually think this will give you an advantage. I imagine that's why in some races they close the wheel with a plastic disc. |
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I'd like to see this done with spiders' thread which is always said to be stronger than a steel wire of the same cross-sectional area. |
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If you have ever seen any old automobile true spoked wheels, they usually have tons of spokes so that part is baked. Auto wheels need more spokes because they deal with side loads so need diagonals in all three dimensions. This is also why they use thicker spokes as the cost and the likelyhood of individual spoke failure goes way up. As for spider silk, I'd ask it's stiffness. Lack of stiffness would turn wheel assembly into a job as hard and as dangerous as tuning a piano because each spoke would have to be tuned like a piano wire and done by reaching between them. Any flawed "spokes" could snap and slice wrists meanly during the process which would be more likely the smaller the spokes get as stress concentrations at the attachment points would be significant. Still interesting so I'm still undecided. |
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[Zeno] The solid wheels reduce forward wind resistance, in trade for greatly increased lateral wind resistance and (usually) extra weight. They are rarely used in situations where significant cross winds are expected. Cross wind resistance is a definite concern. |
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Ok, we will go carefully around corners when the wind is up. Small price to pay for spider wheels. |
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If you make each spoke very thin and have a very large number of them, you have the disc wheel [link]. |
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This will increase both forward and lateral wind resistance. Assuming for simplicity that the total cross sectional area is the same as for conventional spokes, the total frontal area will be more, and they will experience lower Reynolds numbers, so resistance will be greater (in the same way that dust falls more slowly than rocks, and spider webs more slowly than ropes). |
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Although making the spokes thinner and more numerous will increase the surface area, it does not necessarily follow that the forward wind resistance will increase. For example, disc wheels have geater surface area than regular spokes but lower forward wind resistance. |
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A porous, fine-structured object tends to offer more wind resistance than a solid object of the same overall size; that's why practice golf balls have holes in them (so they don't travel as far) and why taping over the air inlets on a car can lower air resistance. A disc wheel acts as a single aerofoil, and so has low air resistance. Decreasing the number of spokes, and making them into individual aerofoils (bladed spokes), is another strategy to decrease air resistance, but with some stiffness sacrificed. |
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I like your idea, but I still think it will increase resistance unless you have so many spokes that little air passes between them, at which point you effectively have a disc wheel. On the other hand, wind resistance in the spokes is probably relatively unimportant unless you are trying to shave off fractions of a second, as in racing. |
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Increaced drag aside, I like this idea. |
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What about tuning the tension patterns to give a wheel that plays a musical chord once you get to certain riding speed? |
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Finding space at the hub and the rim for the 'roots' of the spokes could be tricky, although each spoke could be at a lower tension to the usual, as there are more to spread the load. |
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For any load-bearing task such as this, there is an optimal thickness. As you increase thickness, the volume increases faster than the surface area: in your case, volume would fall much faster than surface area, so there would be greater surface area compared to normal spokes. Volume generally corresponds to strength, |
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I presume the only purpose in doing this would be for the sak eof appearance an ddeemdd beauty: practically, of course it's a loser. |
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Of course, the golden gate bridge could be held up with millions of strands of piano wire, but it's not practical. Don't forget, all that increased surface area means corrosion from the elements will have a greater effect too. |
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JE Gordon, in "The New Science of Strong Materials" argues in
detail why tension is best carried by many finer wires, in
contrast to compression which is best carried in as few as
possible thicker members. |
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And every 'baker should read TNSoSM - it's one of the best 6
books I have ever read. |
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MB if the final result is a wheel that might be irreparably by an errant kick or laydown then put me in the category of Luddite. |
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Yes, but normal people don't expect their bicycles to be
kicked. Or laid down, whatever that is. |
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The logical extension, I suppose, is to have a thin disc in the
stead of spokes. Guess this is also baken. |
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