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#21
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Mechanical Efficiency
On 4/21/2017 11:13 PM, Jeff Liebermann wrote:
On Fri, 21 Apr 2017 20:03:26 -0400, Frank Krygowski wrote: Not true, Jeff. The tension in the chain is a constant The load on each pin in the free upper span is exactly the same, and it doesn't change if the chain is longer, i.e. has more pins. A normal chain with a 100 pound load has 100 pounds on each pin, no matter how long. Argh. We went through this exercise a few years ago in this newsgroup when I allegedly made the same mistake. Am I wrong again? (I just hate it when that happens). Well yes, you're wrong. I don't remember the previous discussion, so I can't comment on the "again" part. The way I look at it is that if I replace each link in the upper part of the chain loop with a spring scale, methinks the deflection of each spring (a measure of the force) would be the pulling load divided by number of spring scales. Nope. Each spring scale would measure the same. If you have two spring scales at home, you can easily verify this. Or, if we break the chain and put one spring scale between two adjacent links, the measured force will be equal to the applied load. However, if we break the chain in two places, methinks the measured force will be half the applied load. If the force were equal to the applied load on each link, I would expect the two spring scales to also indicate a force equal to the applied load, which I don't believe is the case. I'll try a couple other explanations. First, you can find tables of tensile strength for various sizes of roller chain. You'll note that the tables don't specify length. That tensile strength depends on several factors, but not length. If what you're visualizing were true, they'd have to specify length. Second, if what you visualize were true, let's take a chain with an ultimate strength of (say) 5000 pounds. Would that apply to one link (say, 1/2")? If so, would two links (say, 1") be able to hold 10,000 pounds? Would 10 inches of chain be able to hold 100,000 pounds? Would 100" of chain hold a million pounds? You see that it quickly becomes absurd. Under static and otherwise ordinary and reasonable conditions, the length doesn't matter. Tension in a chain is constant over its length. Same is true for ropes, cables, etc. -- - Frank Krygowski |
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#23
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Mechanical Efficiency
On Sat, 22 Apr 2017 00:23:48 -0400, Frank Krygowski
wrote: Nope. Each spring scale would measure the same. If you have two spring scales at home, you can easily verify this. I just took several springs and measured the deflections. You're right which means my explanation is wrong. The last time we had a similar discussion on bicycle chains, I made the same mistake. Something is fundamentally wrong with my reasoning. Argh. First, you can find tables of tensile strength for various sizes of roller chain. You'll note that the tables don't specify length. That tensile strength depends on several factors, but not length. If what you're visualizing were true, they'd have to specify length. Second, if what you visualize were true, let's take a chain with an ultimate strength of (say) 5000 pounds. Would that apply to one link (say, 1/2")? If so, would two links (say, 1") be able to hold 10,000 pounds? Would 10 inches of chain be able to hold 100,000 pounds? Would 100" of chain hold a million pounds? You see that it quickly becomes absurd. Good point and I see the problem. Under static and otherwise ordinary and reasonable conditions, the length doesn't matter. Tension in a chain is constant over its length. Same is true for ropes, cables, etc. Thanks. I'll try not to screw it up again. My usual off topic Drivel: How to mount headlights on a front rack: http://www.cycleexif.com/alex-singer-randonneur Wide headlight pattern using incandescent lights: http://www.bicicletasantigas.com.br/arquivos/portal/galeria/pp118.htm -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#24
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Mechanical Efficiency
On Saturday, April 22, 2017 at 11:14:25 PM UTC-4, Jeff Liebermann wrote:
Snipped My usual off topic Drivel: How to mount headlights on a front rack: http://www.cycleexif.com/alex-singer-randonneur Oh man does that bring back memories. I remember front racks that had an integral clamp to hold your flashlight. Battery powered lights and their mounts sure have come a long ways. Cheers |
#25
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Mechanical Efficiency
On Sat, 22 Apr 2017 21:08:03 -0700 (PDT), Sir Ridesalot
wrote: On Saturday, April 22, 2017 at 11:14:25 PM UTC-4, Jeff Liebermann wrote: Snipped My usual off topic Drivel: How to mount headlights on a front rack: http://www.cycleexif.com/alex-singer-randonneur Oh man does that bring back memories. I remember front racks that had an integral clamp to hold your flashlight. I've never seen one of those racks. You just answered one of my questions. I was wondering if the flashlight mounts were part of the rack design, or added as an accessory. It sure looks like it's part of the rack. Battery powered lights and their mounts sure have come a long ways. Yep. When incandescent flashlights were in fashion, we could barely see or be seen. Today, we have 1000 lumen lights that can glare blind anyone who dares approach. Progress blunders onward. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#26
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Mechanical Efficiency
On 4/22/2017 10:14 PM, Jeff Liebermann wrote:
On Sat, 22 Apr 2017 00:23:48 -0400, Frank Krygowski wrote: -snip- The last time we had a similar discussion on bicycle chains, I made the same mistake. Something is fundamentally wrong with my reasoning. Argh. -snip- One more adult admission like that and you'll be banned from usenet. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#27
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Mechanical Efficiency
On 4/23/2017 10:48 AM, AMuzi wrote:
On 4/22/2017 10:14 PM, Jeff Liebermann wrote: On Sat, 22 Apr 2017 00:23:48 -0400, Frank Krygowski wrote: -snip- The last time we had a similar discussion on bicycle chains, I made the same mistake. Something is fundamentally wrong with my reasoning. Argh. -snip- One more adult admission like that and you'll be banned from usenet. My thought as well. "Admit you're wrong? Whoa, that's against the rules!!" -- - Frank Krygowski |
#28
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Mechanical Efficiency
On Sun, 23 Apr 2017 15:07:39 -0400, Frank Krygowski
wrote: On 4/23/2017 10:48 AM, AMuzi wrote: On 4/22/2017 10:14 PM, Jeff Liebermann wrote: On Sat, 22 Apr 2017 00:23:48 -0400, Frank Krygowski wrote: -snip- The last time we had a similar discussion on bicycle chains, I made the same mistake. Something is fundamentally wrong with my reasoning. Argh. -snip- One more adult admission like that and you'll be banned from usenet. I do wish that someone would ban me from Usenet and put me out of my misery. I spend far too much time providing wrong answers, misleading theories, bizarre designs, worthless ideas, and topic drift. My thought as well. "Admit you're wrong? Whoa, that's against the rules!!" Please forgive my breach of protocol. To err is human and I just wanted to reassure myself. Feel free to assume that I'm perfect. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#29
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Mechanical Efficiency
On Saturday, April 22, 2017 at 8:14:25 PM UTC-7, Jeff Liebermann wrote:
Thanks. I'll try not to screw it up again. Fat chance. Bet I beat you to the punch though. |
#30
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Mechanical Efficiency
On Friday, April 21, 2017 at 8:31:27 PM UTC-7, Jeff Liebermann wrote:
On Fri, 21 Apr 2017 10:40:30 -0700 (PDT), Doug Landau wrote: So you are saying that losses from routing the lower run of the chain through tensioners and idlers are negligible? Worse. I was ignoring the losses from tensioners, idlers, grease, pin rotation caused by a slight chain droop, inertial loading from a longer and thus heavier chain, chain acceleration lag, etc. I assumed that the original question was about a simple power transmission system, not the complex mess that such systems inevitably evolve into. Something more like this test fixture and a practical bicycle: http://cdn.mos.bikeradar.imdserve.com/images/news/2012/11/06/1352163122826-1476emv18vmdi-630-80.jpg The additional losses can be tested separately and included later. You're correct that tensioners, idlers, etc are important. I'm not saying they are I'm just wondering. It doesn't look like the losses from the derailer on an upright is going to be significant. What I noticed with my rickshaw was that the chain was so long it was hard to keep off the ground due to it's weight. I tried using a derailer as a tensioner, and mounted it upside-down underneath the cab,so the spring would lift it up, near the middle of the run. To my surprise the spring wasn't anywhere near stiff enough. Not even enough to keep the pulleys engaged, let alone the chain held up above level, let alone taught and not flapping. It's what it was going to take to take up the slack that I thought might be non-negligible. |
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