- #1

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https:///watches/moon-phase/tech-specs/

my calculation is 1/(2/12*14/18*14/109)/2=30.03

which is different from its result 29.53089 days.

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- Thread starter Don Wong
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- #1

- 2

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https:///watches/moon-phase/tech-specs/

my calculation is 1/(2/12*14/18*14/109)/2=30.03

which is different from its result 29.53089 days.

- #2

Mech_Engineer

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- #3

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I have read that wiki before, but i think this question doesn't require the knowledge of the lunar phase system. It is just the calculation of the gear ratio as it states in the website.

- #4

Baluncore

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Your ratio is assuming that the arm with the gears is fixed while the 109 tooth ring rotates. That is back to front. The arm that carries the moon rotates counter-clockwise once each lunar cycle, complete with the gear train. You must allow for that one turn advance of the first gear over each lunar period.

12 hours is half a day so a quick estimate gives a period closer to 30.03 – 0.5 = 29.53 days.

- #5

Baluncore

Science Advisor

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So the compound gear ratio becomes;

(12/14) * (18/14) * ( 109 / 2 ) = 60.0612244898

Next remove the epicyclic backward turn of the arm from the simple ratio;

60.0612244898 – 1 = 59.0612244898

The input period is 12 hours = 0.5 day, so the output period is;

59.0612244898 * 0.5 day = 29.5306122449 days.

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