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Re: program to compute gears, with table
From: |
Skip Montanaro |
Subject: |
Re: program to compute gears, with table |
Date: |
Fri, 8 Sep 2017 06:09:30 -0500 |
Something's fishy. Is the result mm of forward travel per crank revolution?
I'm used to seeing gear inches. Your 50x12 should be about 110 gear inches.
If your output is in millimeters, I get about 320 gear inches, so either
I've mistaken your intended units, or there's a mistake in there somewhere.
A couple nits which won't change anything:
* Why the 1.0 divisor when computing gear?
* You can skip the radius and use wheel (diameter) directly in computing
the circumference.
* It never occurred to me to do this in Lisp. I always just use an online
calculator, like:
http://www.gear-calculator.com/?GR=DERS&KB=34,50&RZ=12,13,15,17,19,21,23,25&UF=2150&TF=90&SL=2.6&UN=KMH
Skip
P.S. My latest acquisition (and oldest bike):
https://www.flickr.com/photos/49705339@N00/albums/72157686279443084
On Fri, Sep 8, 2017 at 12:33 AM, Emanuel Berg <moasen@zoho.com> wrote:
> Hey guys, does this look right to you?
>
> ;; (print-gears '(34 50) '(12 13 15 17 19 21 23 25) 622)
> ;;
> ;; =>
> ;;
> ;; 622 wheel
> ;;
> ;; chainring sprocket gear
> ;;
> ;; 34 25 2657.5360544880004
> ;; 34 23 2888.626146182609
> ;; 34 21 3163.7333982000005
> ;; 34 19 3496.7579664315795
> ;; 50 25 3908.1412566000004
> ;; 34 17 3908.1412566000004
> ;; 50 23 4247.97962673913
> ;; 34 15 4429.226757480001
> ;; 50 21 4652.549115000001
> ;; 34 13 5110.64625863077
> ;; 50 19 5142.291127105264
> ;; 34 12 5536.5334468500005
> ;; 50 17 5747.266553823531
> ;; 50 15 6513.568761
> ;; 50 13 7515.656262692309
> ;; 50 12 8141.960951250001
>
> (require 'cl-lib)
>
> (defun compute-gear (chainring sprocket wheel)
> (let*((pi 3.14159265)
> (radius (/ wheel 2.0))
> (circum (* 2 radius pi))
> (gear (* (/ chainring sprocket 1.0) circum)))
> (list chainring sprocket gear)))
>
> (defun gear (chainrings sprockets wheel)
> (let*((gears
> (cl-loop for c in chainrings
> append (cl-loop for s in sprockets
> collect (compute-gear c s wheel) )
> )))
> (cl-sort gears #'<= :key #'cl-caddr)))
>
> (defun print-gears (chainrings sprockets wheel)
> (let ((out-buffer (get-buffer-create "*Gears*")))
> (with-current-buffer out-buffer
> (erase-buffer)
> (insert (format "%s wheel\n\n" wheel))
> (insert "chainring sprocket gear\n\n")
> (let ((gears (gear chainrings sprockets wheel)))
> (cl-loop for g in gears
> do (let ((c ( car g))
> (s ( cadr g))
> (d (cl-caddr g)))
> (insert (format " %s %s %s\n" c s
> d)) ))))
> (pop-to-buffer out-buffer) ))
>
> --
> underground experts united
> http://user.it.uu.se/~embe8573
>
- program to compute gears, with table, Emanuel Berg, 2017/09/08
- Re: program to compute gears, with table, Graham, 2017/09/08
- Re: program to compute gears, with table,
Skip Montanaro <=
- Re: program to compute gears, with table, David Scheidt, 2017/09/08
- Message not available
- Re: program to compute gears, with table, Emanuel Berg, 2017/09/08
- Re: program to compute gears, with table, Joerg, 2017/09/08
- Re: program to compute gears, with table, David Scheidt, 2017/09/08
- Re: program to compute gears, with table, Emanuel Berg, 2017/09/08
- Re: program to compute gears, with table, Joerg, 2017/09/09
- Re: program to compute gears, with table, Emanuel Berg, 2017/09/09