On Friday, September 8, 2017 at 8:50:36 AM UTC-7, Frank Krygowski wrote:
On 9/8/2017 4:46 AM, Graham wrote:

"Emanuel Berg" wrote in message ...
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/resource..._chart_ENG.pdf

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

Graham.

Right, don't forget to include the tire. 622 is bead seat diameter, but
you want (effective) outside diameter instead.

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

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.

These days, it's probably easiest to do all the above using a
spreadsheet, such as LibreOffice Calc. Or Micros**t Excel.

BTW, back when there were only five rear cogs and a person wanted a wide
range with uniform or other logical spacing, plotting gear development
(or "gear inches," in "inch" countries) was a useful tool for the art of
bike design. These days, with up to 11 cogs in back, the entire exercise
isn't as valuable as it once was.

Almost the entire automobile industry is being programmed with languages like Python. Like Fortran these higher level languages are easy and fast to correct errors but everything is on the net now - Tesla updates all of their software off of the Internet.

Higher level languages have millions of holes in them for hackers to gain control of your system. How would you like all of the traffic lights in your area to turn red at once and stay that way? How would you like pressing the accelerator on your car to act as a brake or visa versa? Being interviewed by electric car manufacturers for development jobs I can't seem to get it through their heads that they are placing their company's in grave danger by using languages that are not certifiable.

Even the people that write in Assembly language don't do it as I do. They write utility groups and then simply make calls to these utilities. This is so clumsy that I write smaller, more compact and faster code in C. Though in general these assembly code groups are relatively safe compared to the higher level languages.