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#1
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$39 test device for forces on spokes
While sitting at my computer, I happened to pick up a roll of a
hundred 39-cent stamps, packed by the US Post Office in a tight plastic wrapping. A moment later, I noticed that I was holding the natural enemy of such packaging in my other hand, namely a ball-point pen. I can resist anything except temptation, so . . . Whonk! http://www.filelodge.com/files/room1...st%20wheel.jpg or http://tinyurl.com/otx8z If you click on the lower right of the picture in Explorer, you get a huge view, detailed enough to show the stretch-marks on the plastic wrapping, indicating tension of some kind. While expensive, a roll of stamps should eventually be within everyone's reach. (I suppose that the post office will sell you a roll of hundred 1-cent stamps for just a buck, but I must caution you against using cheap materials.) Anyway, it's a fun and easy-to-play-with model. Is the plastic "spoking" in tension? If you push the pen "axle" sideways, then it certainly is. Apply a load to the pen "axle" and see the upper "spoking" pull away from the pen-axle while the stamp "rim" flattens slightly. I doubt that anything terribly new is happening, but it may provide harmless entertainment for the usual debate. You could make a bigger model by stretching some inner-tube rubber across the mouth of a tin can. Explaining the details should be a good exercise for anyone tired of wagon wheels, cast wheels, and pre-tensioned spoked wheels. Cheers, Carl Fogel |
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#3
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$39 test device for forces on spokes
wrote: While sitting at my computer, I happened to pick up a roll of a hundred 39-cent stamps, packed by the US Post Office in a tight plastic wrapping. A moment later, I noticed that I was holding the natural enemy of such packaging in my other hand, namely a ball-point pen. I can resist anything except temptation, so . . . Whonk! http://www.filelodge.com/files/room1...st%20wheel.jpg or http://tinyurl.com/otx8z Wow, look at that naturally high "spoke" count. Apparently, nature abhors low spoke count wheels! |
#4
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$39 test device for forces on spokes
"Earls61" wrote:
wrote: Whonk! http://www.filelodge.com/files/room1...st%20wheel.jpg or http://tinyurl.com/otx8z Wow, look at that naturally high "spoke" count. Apparently, nature abhors low spoke count wheels! What - "one" is "high"? ;-) Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $795 ti frame |
#5
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$39 test device for forces on spokes
On 2006-09-30, wrote:
While sitting at my computer, I happened to pick up a roll of a hundred 39-cent stamps, packed by the US Post Office in a tight plastic wrapping. A moment later, I noticed that I was holding the natural enemy of such packaging in my other hand, namely a ball-point pen. I can resist anything except temptation, so . . . Whonk! http://www.filelodge.com/files/room1...st%20wheel.jpg or http://tinyurl.com/otx8z If you click on the lower right of the picture in Explorer, you get a huge view, detailed enough to show the stretch-marks on the plastic wrapping, indicating tension of some kind. Maybe that's plastic deformation caused as the pen was shoved in. I don't believe the resulting wheel can be pretensioned since nothing is actually glued to the pen. While expensive, a roll of stamps should eventually be within everyone's reach. (I suppose that the post office will sell you a roll of hundred 1-cent stamps for just a buck, but I must caution you against using cheap materials.) Anyway, it's a fun and easy-to-play-with model. Is the plastic "spoking" in tension? If you push the pen "axle" sideways, then it certainly is. Apply a load to the pen "axle" and see the upper "spoking" pull away from the pen-axle while the stamp "rim" flattens slightly. Certainly wheel-building would be easier if all you had to do was ram the hub in through some plastic wrapping... Explaining the details should be a good exercise for anyone tired of wagon wheels, cast wheels, and pre-tensioned spoked wheels. For those tired of wheels altogether, it may also be interesting to reflect that space elevators use the same principle as the bicycle spoke. It's the pretension in the cable that stops the orbiting skyhook coming down to Earth when you winch something up the cable. As the load climbs up the cable, the stretch of cable behind the load, between it and the ground, goes a bit slacker, but the tension in the cable above the load all the way up to the orbiting satellite stays the same. |
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