Re: Spoke tension meter-John Allen responds



[email protected] wrote:

> <[email protected]> wrote:
>> Oop! Sorry Carl, not only is this not clear, it's not even correct!
>> Only the straight portion of the wire will have no net tension using
>> this method.
>>
>> This doesn't affect anything that Luns has said on the subject, however.

>
> Dear Benjamin,
>
> Would this be the idea?
>
> T
> O T
> N --> N N N N N N
> FFFFFFFFFFFFFFF
>
> N = no-tension straight portion of wire
> F = flat surface
> O = round pen wire is being coiled around
> T = wire under tension
>
> That is, the tension bends the wire upward as it rolls
> counter-clockwise onto the pen?


Yes, exactly. (This is not how Luns made his spring, though).

In fact, I believe that if you properly constrained the wire, you could
make a preloaded spring where the bending was done under a net compression.
For example, look at the wire in the process of being wrapped on the page
Luns has showed us. Now, with the wire frozen in place, hollow it out so
that it forms a hollow cylinder, and imaging *pushing* a wire through this
cylinder.

I'm sure there's an easier way to do this, but that should provide a
sufficient conceptual picture to see that it can be done.


--
Benjamin Lewis

"Love is a snowmobile racing across the tundra and then suddenly it flips
over, pinning you underneath. At night, the ice weasels come."
--Matt Groening
 
On Mon, 27 Jun 2005 13:34:31 -0700, Benjamin Lewis
<[email protected]> wrote:

>[email protected] wrote:
>
>> <[email protected]> wrote:
>>> Oop! Sorry Carl, not only is this not clear, it's not even correct!
>>> Only the straight portion of the wire will have no net tension using
>>> this method.
>>>
>>> This doesn't affect anything that Luns has said on the subject, however.

>>
>> Dear Benjamin,
>>
>> Would this be the idea?
>>
>> T
>> O T
>> N --> N N N N N N
>> FFFFFFFFFFFFFFF
>>
>> N = no-tension straight portion of wire
>> F = flat surface
>> O = round pen wire is being coiled around
>> T = wire under tension
>>
>> That is, the tension bends the wire upward as it rolls
>> counter-clockwise onto the pen?

>
>Yes, exactly. (This is not how Luns made his spring, though).
>
>In fact, I believe that if you properly constrained the wire, you could
>make a preloaded spring where the bending was done under a net compression.
>For example, look at the wire in the process of being wrapped on the page
>Luns has showed us. Now, with the wire frozen in place, hollow it out so
>that it forms a hollow cylinder, and imaging *pushing* a wire through this
>cylinder.
>
>I'm sure there's an easier way to do this, but that should provide a
>sufficient conceptual picture to see that it can be done.


Dear Benjamin,

Actually, I suspect that even that method is too simple for
forming a coil in compression:

You not only have to have two restraining surfaces for the
circular drum part:

))

(Imagine that going all the way around.)

You also have to have a restraining feed:

) )
_________________/ /
_____>___>_____> /
_______>___>______/


Without a close-fitting restraining tube in which rolling
pads force the wire forward in a straight line, the wire
will buckle as soon as the bend it's being pushed into is
sharp enough to raise the compression over the buckling
load.

You know, when the plumbing snake hits a sharp bend or
dreadful obstruction x and the springy wire bends uselessly
sideways in your hands outside the pipe, inside of which
it's still constrained:

\ \
pipe | x |
snake buckle ==========/ | |
---------------/\-----------' /
compressive ============/
force -->

Carl Fogel
 
[email protected] wrote:

> <[email protected]> wrote:


>> In fact, I believe that if you properly constrained the wire, you could
>> make a preloaded spring where the bending was done under a net
>> compression. For example, look at the wire in the process of being
>> wrapped on the page Luns has showed us. Now, with the wire frozen in
>> place, hollow it out so that it forms a hollow cylinder, and imaging
>> *pushing* a wire through this cylinder.
>>
>> I'm sure there's an easier way to do this, but that should provide a
>> sufficient conceptual picture to see that it can be done.

>
> Dear Benjamin,
>
> Actually, I suspect that even that method is too simple for
> forming a coil in compression:
>
> You not only have to have two restraining surfaces for the
> circular drum part:
>
> ))
>
> (Imagine that going all the way around.)
>
> You also have to have a restraining feed:


You misunderstand me. My restraining feed is the hollowed-out wire from
the web page Luns showed us. (i.e. instead of a wire, it's now a pipe).

--
Benjamin Lewis

"Love is a snowmobile racing across the tundra and then suddenly it flips
over, pinning you underneath. At night, the ice weasels come."
--Matt Groening
 
Carl, Jobst, or anyone,

I need a value for the radial stiffness of a wheel. Previously I
extracted values from the finite element data in "The Bicycle Wheel".
Alas, no mention is given of the spoke diameter used in the
simulation. In the "Torsional Stiffness of Spoking" table,
a diameter of 1.6mm is used. Maybe that is the value used for the
simulation. Does a later edition have more information?


Joe
 
Joe Riel wrote:
> Carl, Jobst, or anyone,
>
> I need a value for the radial stiffness of a wheel. Previously I
> extracted values from the finite element data in "The Bicycle Wheel".
> Alas, no mention is given of the spoke diameter used in the
> simulation. In the "Torsional Stiffness of Spoking" table,
> a diameter of 1.6mm is used. Maybe that is the value used for the
> simulation. Does a later edition have more information?
>
>
> Joe


How about Francois Grignon's data?
http://www.sheldonbrown.com/rinard/wheel/grignon.htm

Details are at the link above, but here are the radial stiffnesses:

Wheel Radial stiffness(lb/in)
Shamal 12 HPW 12 600
Zipp 540 20 200
Mavic Cosmic Expert 13 500
Cane Creek Crono 8800
Specialized tri-spoke 8400
Campagnolo 32 spokes 13 500
Mavic 36 spokes 20 200