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Mechanical Efficiency



 
 
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  #21  
Old April 22nd 17, 05:23 AM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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Posts: 10,538
Default 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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  #22  
Old April 22nd 17, 08:51 PM posted to rec.bicycles.tech
[email protected]
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Posts: 3,345
Default Mechanical Efficiency

On Friday, April 21, 2017 at 8:54:33 PM UTC-7, Jeff Liebermann wrote:
On Fri, 21 Apr 2017 10:18:17 -0700 (PDT), wrote:

Huh? These long chains do not have straight runs and in fact near the
back have a rather shorter run to the cogs which always puts them in
more of a sharper angle to the cogset. In other words - you are
always in a more "cross-chained" angle.


There are chain designs which help in such arrangements. This one
seems popular:
http://kmcchain.us/chain/x9-93/
http://t-cycle.com/chain-in-bulk-c-116/bulk-kmc-x993-chain-by-foot-p-35.html

However, if you're looking for the source of chain drag and friction,
just look at what wears on an old chain. It's not the inner or outer
plates, which is what allegedly wears with "bent" chain line. It's
the pin and sleeve that show most of the wear and presumably is the
source of most of the friction. I say presumably because there are
differences in surface hardness, lubrication, cleanliness, etc which
affect wear.
--
Jeff Liebermann

150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558


I read and article that tested chains and new they were all equal. But the KMC wore more rapidly and the friction went up faster. Though with the price difference you could buy three KMC chains for one Campy.
  #23  
Old April 23rd 17, 04:14 AM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 4,018
Default 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  
Old April 23rd 17, 05:08 AM posted to rec.bicycles.tech
Sir Ridesalot
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Posts: 5,270
Default 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  
Old April 23rd 17, 06:51 AM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 4,018
Default 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  
Old April 23rd 17, 03:48 PM posted to rec.bicycles.tech
AMuzi
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Posts: 13,447
Default 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  
Old April 23rd 17, 08:07 PM posted to rec.bicycles.tech
Frank Krygowski[_4_]
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Posts: 10,538
Default 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  
Old April 23rd 17, 09:44 PM posted to rec.bicycles.tech
Jeff Liebermann
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Posts: 4,018
Default 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  
Old April 23rd 17, 11:03 PM posted to rec.bicycles.tech
[email protected]
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Posts: 3,345
Default 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  
Old April 25th 17, 08:21 PM posted to rec.bicycles.tech
Doug Landau
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Posts: 1,424
Default 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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