[OpenSCAD] Mayan calendar

Dan Shriver tabbydan at gmail.com
Mon Jan 15 18:19:23 EST 2018

Thanks Chris and especially Ronaldo.

I'm still digesting Ronaldo's solution (I confess to being a bit slow about

I was wondering about the Antikythera mechanism too (forgot its name, which
I should commit to memory as it is the first computer).  Also wondering
about old clock that would mechanically put the day of the month.

I'm trying to make the mechanism with as few parts / gears as I can, but
also I want to separate the different cycles (day of month, vs month of


On Mon, Jan 15, 2018 at 7:17 AM, Chris Camacho <chris at bedroomcoders.co.uk>

> it might be worth your while to research the antikythera mechanism
> especially the fractional gears
> I never knew you could half a gear tooth... with different ratios with
> fractions you should be able to reduce the need to have long sectional
> gears (hopefully)
> On 14/01/18 22:11, Ronaldo Persiano wrote:
> Hi, Dan.
> I have worked a bit on the idea of using sectional gears to solve your
> quest about the month wheel in the Mayan Calendar Round. I designed two
> sectional gears: one for the month wheel and one for the year wheel. The
> first one has 76 teeth (one for each 5 days) with 7 missing teeth. The year
> wheel has 73 teeth (one for each 5 days as well) with no missing teeth. The
> missing teeth of the month gear allow that the wheel rotates 4 times faster
> them usually during the short month transition. The included animated gif
> shows the transition of 5 "unlucky days". Another pair of sectional gears
> would be responsible for this transition (I haven't designed them). The
> design of the two shown gears is not correct yet because of a small tooth
> crash at the beginning and ending of the transition but some "light
> filling" of two teeth of the month gear would solve that.
> Animation: MonthTransition.gif
> Animation code: mayanSGears.scad
> Month gear: monthGear76_7.svg
> Year gear: yearGear73.svg
> In this design, the two wheels have approximately the same big diameter. I
> don't see any way to avoid that.
> 2018-01-12 20:12 GMT-02:00 Ronaldo Persiano <rcmpersiano at gmail.com> <rcmpersiano at gmail.com>:
> I tried to design my idea but failed: I don't think Geneva drive would do
> the trick. In fact, I think now a better solution for your quest would be
> to consider a variable sectional gear mechanism like the one is found in Gearwheels
> from Hell <http://www.douglas-self.com/MUSEUM/POWER/gear/gear.htm> <http://www.douglas-self.com/MUSEUM/POWER/gear/gear.htm>. Those
> mechanisms allow to have two or more gear transmission ratio during the
> rotation. But don't ask how, at least not now. :)
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