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program to compute gears, with table



 
 
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  #11  
Old September 8th 17, 10:23 PM posted to rec.bicycles.tech
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Default program to compute gears, with table

On Friday, September 8, 2017 at 10:45:07 AM UTC-7, Emanuel Berg wrote:
Graham wrote:

So if your definition of gear is roll out in
mm then it looks close. Do not forget to
include the tyre.


Right, perhaps I should change "gear" into
"roll out" if that's the agreed-upon term.
Perhaps I should even make it print the
formulae first thing.

And I'll include the tyre. Excellent


There's always a slight error this way. The radius of a tire and hence it's circumference changes slightly with pressure and/or weight of the rider.
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  #12  
Old September 8th 17, 10:32 PM posted to rec.bicycles.tech
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Default program to compute gears, with table

On Friday, September 8, 2017 at 10:52:22 AM UTC-7, Emanuel Berg wrote:
Skip Montanaro wrote:

* Why the 1.0 divisor when computing gear?


As explained, otherwise it'll be integer
division. But I think that qualifies as a hack
(not an ugly hack tho) so there is no shame in
spotting it an "error"

* You can skip the radius and use wheel
(diameter) directly in computing
the circumference.


Right!

* It never occurred to me to do this in Lisp.
I always just use an online calculator, like:

http://www.gear-calculator.com/?GR=D...&SL=2.6&UN=KMH


Let's agree there is no need to do it in Lisp.
Only a desire


That's an eight speed setup. For the most part you can REALLY set an 8 speed up nicely to have only two clumsy steps - the two highest gears. And you in general only use these while riding downhills so it is not worth making these ratios closer.

So exactly why are they changing to 10, 11 and now 12 speeds. These have weaker chains, much faster wearing drive components and less sure shifting.
  #13  
Old September 8th 17, 10:56 PM posted to gnu.emacs.help,rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 417
Default program to compute gears, with table

Frank Krygowski wrote:

I first did such a thing in the 1970s, using
Fortran.


Cool! Fortran (Formula Translation, 1957)
sounds like the perfect idea. Perhaps the
formating (output report) should be left to
COBOL tho (Common business-oriented
language, 1959).

Today I think the hipsters at the universities
would use Haskell (1990).

But I formatted it as a compact table in rows
and columns. You could have one row for each
chainring, one column for each rear cog.
A matrix, 2x8.


The idea with having it 8x3 was that the third
column would be the "roll out" and that would
be sorted vertically.

But perhaps I'll add a feature to flip
it later.

Another useful trick is to plot the gear
development on a logarithmic scale, so the
change from one gear to the next is scaled as
the percentage change. Plotting using
a separate row or a separate symbol for each
chainring makes clear which gear is "next" in
your gear progression.


Yes, I thought about doing that. Perhaps with
ASCII art or using gnuplot which I did some
cool plots with. Here is one:

http://user.it.uu.se/~embe8573/figur...e-inverted.png

--
underground experts united
http://user.it.uu.se/~embe8573
  #14  
Old September 9th 17, 12:45 AM posted to gnu.emacs.help,rec.bicycles.tech
Emanuel Berg[_2_]
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Default program to compute gears, with table

David Scheidt wrote:

The style is awful. In straight
common lisp [...]


Ha! I've heard about the bicycle style police
but I always thought that refered to shaved
legs and keeping the helmet straps to the
inside of the sunglasses scalps! Or wait...
should it be the other way around?

Well, styles make fights, and "pushing" is
never part of my game plan. But it does look
neater with `dolist' and `push' and it might be
more efficient as well as I don't know the
intricacies of append and collect. Not that it
will ever matter in this case, of course.

--
underground experts united
http://user.it.uu.se/~embe8573
  #15  
Old September 9th 17, 12:51 AM posted to gnu.emacs.help,rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 417
Default program to compute gears, with table

Joerg wrote:

Why make things complicated?


It isn't - it's fun

I do such stuff with spreadsheets.


When done, feeding a CLI tool with data from
the shell is faster and more pleasant (cooler)
than using a spreadsheet. It can then also be
combined with other such tools, tho I admit
that probably won't happen in this case (?).

A spreadsheet is of course a fine way to do it
as well.

That's what they were invented for.


Programming languages were also invented for
this kind of... computing

--
underground experts united
http://user.it.uu.se/~embe8573
  #16  
Old September 9th 17, 12:55 AM posted to gnu.emacs.help,rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 417
Default program to compute gears, with table

David Scheidt wrote:

I rewrote his code in common lisp in less
time than it takes excel to start.


It really doesn't get any faster than these
lovely small shell tools


you gotta give me more and more
cuz you're the one that I adore
(Zodiac 1996)


--
underground experts united
http://user.it.uu.se/~embe8573
  #17  
Old September 9th 17, 05:29 AM posted to rec.bicycles.tech
John B.[_3_]
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Posts: 3,652
Default program to compute gears, with table

On Fri, 8 Sep 2017 14:32:52 -0700 (PDT), wrote:

On Friday, September 8, 2017 at 10:52:22 AM UTC-7, Emanuel Berg wrote:
Skip Montanaro wrote:

* Why the 1.0 divisor when computing gear?


As explained, otherwise it'll be integer
division. But I think that qualifies as a hack
(not an ugly hack tho) so there is no shame in
spotting it an "error"

* You can skip the radius and use wheel
(diameter) directly in computing
the circumference.


Right!

* It never occurred to me to do this in Lisp.
I always just use an online calculator, like:

http://www.gear-calculator.com/?GR=D...&SL=2.6&UN=KMH

Let's agree there is no need to do it in Lisp.
Only a desire


That's an eight speed setup. For the most part you can REALLY set an 8 speed up nicely to have only two clumsy steps - the two highest gears. And you in general only use these while riding downhills so it is not worth making these ratios closer.

So exactly why are they changing to 10, 11 and now 12 speeds. These have weaker chains, much faster wearing drive components and less sure shifting.


But they do allowed the sales person to say such things as "Of course
it has the new x speed" system. The last time I was at my local bike
shop the sales person said something about, "well, we do still have a
few 9 speed chains left".

I might add that in Bangkok, which is essentially flat, I might use
two gears on a normal ride.
--
Cheers,

John B.

  #18  
Old September 9th 17, 05:46 AM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 417
Default program to compute gears, with table

John B. wrote:

"well, we do still have a few 9 speed chains
left".


Anyone feel free to elaborate on this. How and
why should the chain be different with
different cassette/chainring configurations?

And is there a "notation" do describe this?
Usually makes it easier to understand...

--
underground experts united
http://user.it.uu.se/~embe8573
  #19  
Old September 9th 17, 08:00 AM posted to rec.bicycles.tech
John B.[_3_]
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Posts: 3,652
Default program to compute gears, with table

On Sat, 09 Sep 2017 06:46:59 +0200, Emanuel Berg
wrote:

John B. wrote:

"well, we do still have a few 9 speed chains
left".


Anyone feel free to elaborate on this. How and
why should the chain be different with
different cassette/chainring configurations?

And is there a "notation" do describe this?
Usually makes it easier to understand...


The rear sprocket spacing is closer as the number of cassette cogs
goes up, so narrower chains.

The over all length of the cassette is limited by the distance between
the rear drop outs as the wider the cassette the more the hub flange
on that side must be offset and thus the angle of the spokes
decreases.
--
Cheers,

John B.

  #20  
Old September 9th 17, 11:37 AM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 417
Default program to compute gears, with table

John B. wrote:

The rear sprocket spacing is closer as the
number of cassette cogs goes up, so
narrower chains.

The over all length of the cassette is
limited by the distance between the rear drop
outs as the wider the cassette the more the
hub flange on that side must be offset and
thus the angle of the spokes decreases.


Okay? Is that the reason you simply cannot make
the back fork wider? At some point the spoke
angle will make for a wheel that isn't
strong enough?

--
underground experts united
http://user.it.uu.se/~embe8573
 




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