Re: program to compute gears, with table

["Graham" <h2gt2g42-micenewgroups@yahoo.co.uk>]

"Emanuel Berg" <moasen@zoho.com> wrote in message news:86bmmlu54a.fsf@zoho.com...
> 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

Not sure about your code as I do not speak that language but a quick check gives:

622*3.142*50/25=3908.648mm

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

https://www.cateye.com/data/resources/Tire_size_chart_ENG.pdf

for approximate circumferences. Taking a 23mm tyre the above example would be:
2096*50/25=4192mm

Graham.

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