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sansbury
03-19-2011, 11:42 AM
I've been nibbling away at building an orrery for a while but recently had a twist of thought to do a "modernized" device inspired by the Antikythera Mechanism, to track dates of modern significance like the 4th of July, Thanksgiving, and others that can be determined by simple rules.

What I am looking for are starting points for the mechanics of the thing, and it occurred to me that the first major part of this is a perpetual calendar. I figure once I have days and months ticking by, I can easily trap conditions like "third Thursday of the eleventh month".

Anyway, I don't have a lot of preconditions other than I want a completely mechanical solution. I'm open to something that is more clockwork-like or binary/computational in principle, though I'd want to avoid designs that require jet-engine precision or that require me to build something on the order of a Babbage engine :D

Any ideas?

Mike Burdick
03-19-2011, 12:05 PM
I'm sure you have already googled this, but ....

http://lisaboyer.com/Claytonsite/celestialmechanical.jpg

http://lisaboyer.com/Claytonsite/celestialmechanicalpage.htm

.

Weston Bye
03-19-2011, 12:25 PM
My first pass speculation involves a set of geneva wheels of varying stations arranged like an odometer. the first stage, 7 stations for day. The next becomes more complicated: months are supposed to alternate between 30 and 31 days, but the Romans screwed that up royally, or more accurately imperially, with tributes to Julius and Agustus, and February, getting shorted in the deal. The simplest path would be to use a 365 station geneva wheel, (easier than it would seem but a fairly large diameter wheel) except for the additional complication of the leap year injecting an extra day....

That path came to a dead end, perhaps this:

A series of escapement wheels, each with its own escapement.
24 hr clock trips a 7 day wheel, and a 31 day wheel
31 day wheel works with a 48 month (4 years) wheel containing cams that work back to the 31 day wheel to cause escapement to bypass 29th, 30th or 31st day as required.

Each escapement would have to have its own driving weight or spring. Cams on the various wheels would raise flags for significant dates when all the required cams were in alignment, much like a combination lock.

There...more food for thought.

I wonder if Rube Goldberg and I share any common ancestors.

sansbury
03-19-2011, 02:30 PM
@Mike: That site is new to me--thanks!

@Weston: Now you have me thinking about a transmission with 31:1, 30:1, 29:1, and 28:1 ratios and some type of cam that selects the ratio once per revolution....

jeastwood
03-23-2011, 09:31 PM
I recommend "Geared to the Stars" as the best orrery book I know of. It should have some date mechanisms.

Best regards,

Jeff E.

sansbury
03-23-2011, 10:15 PM
Holy $#@!--used copies start at $320 on Amazon. It better be good!

The Artful Bodger
03-23-2011, 10:28 PM
I once dismantled an old factory time stamping machine, the device workers put their cards into at the start and end of each shift. This one had a basic clock showing hours and minutes and of course the print wheels which included days of the week and months, it might have even had years.

The whole thing was 'programmed' with plug chains!
http://image.made-in-china.com/2f0j00IvyTGdDFCPcE/Chain-Spool.jpg

The chains ran over sprockets which were not ordinary sprockets more like pullies with holes to accommodate each metal ball. There were bigger balls at intervals which were formed by clamping a thin metal shell over the ball, the change in diameter was not much but it was enough to trip micro switches as the ball passed over a sprocket.

The chains were in loops of different sizes and one extra long one may have had a ball for every hour of the month.

The guy who gave it to me said it could even handle leap years and would turn the factory lights on and off excluding weekends.

If I recall correctly it was of Australian manufacture. Sadly it has long ago been reduced to it smallest component parts though I did keep one sprocket and chain which is stored "in a safe place".

The loops of chain were fed into a 'tower' where they piled up somewhat and were pulled from the bottom so really the machine was more compact than one might have expected.

Evan
03-23-2011, 11:40 PM
Build a mechanical computer. First you need a mechanism that advances once every 24 hours (at least). That is simple enough, it's called a clock.

Next is the programming system. There are a variety of ways to do this. One is a metal tape with holes punched in various tracks. A drum or a disk has also been used for similar functions in the past. In particular a drum can have multiple spiral tracks much like a 12 start thread that is programmed with pins that stick out like a music box drum. The drum is advanced daily on a screw that brings it past a stationary "reader" where the pins mechanically actuate various mechanisms that move indicators as required. This can easily run for a full year and a decade is possible before a reset is required.

A system like this can be programmed with any number of cycles including lunar, the planets and even the equation of time for sunrise and sunset. Holidays and leap years are trivial.

aostling
03-24-2011, 12:12 AM
Holidays and leap years are trivial.

Is predicting Easter trivial? It always surprises me.

Evan
03-24-2011, 04:00 AM
Easter being a movable feast that follows technically incorrect astronomical cycles makes the calculation independent of the scientific calculation of the lunar cycles. How it is calculated depends on whose Easter you wish to observe. Easiest in such a case is to program in the precalculated dates.

Really, the same applies to any calendar that makes reference to the positions of observed celestial objects in general since it is only valid for the epoch for which it is calculated. For real accuracy the Julian date should be used. This is not related to the Julian calendar. The Julian date is the count of standard days (and decimal fraction) that have elapsed noon universal time (UT), 1 January 4713 BC. That then simplfies the calculation of any calendrical date. The Julian date is used by astronomers since it eliminates any confusion over when an observation was made.

The observation of any astronomical object is subject to variability that cannot be calculated, only observed. The positions of objects as seen in the sky is affected by inherently unpredictable factors. The rotation and position of the Earth is constantly changing and is influenced by the weather, earthquakes and variation in the orbits of solar system celestial bodies that cannot be predicted.

SGW
03-24-2011, 07:38 AM
Artful - that chain-programming mechanism really appeals to my sense of weirdness!

jeastwood
03-24-2011, 09:32 PM
Holy $#@!--used copies start at $320 on Amazon. It better be good!

Interlibrary loan is one way to get your hands on a copy; the NAWCC library will also loan it out for the cost of postage, if you are a member.

Regards,

Jeff E.

madwilliamflint
03-24-2011, 09:56 PM
Artful - that chain-programming mechanism really appeals to my sense of weirdness!

Read Neil Stephenson's "The Diamond Age".

The Artful Bodger
03-24-2011, 10:46 PM
Artful - that chain-programming mechanism really appeals to my sense of weirdness!


I hunted it out and took a couple of pictures, just for you!:p

As it appears when used, two chains in this one..
http://farm6.static.flickr.com/5299/5557104579_a0b3980678.jpg (http://www.flickr.com/photos/25239206@N06/5557104579/)
IMGP9188 (http://www.flickr.com/photos/25239206@N06/5557104579/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), on Flickr


This is the chain from just one half of the unit...
http://farm6.static.flickr.com/5303/5557104315_c51179d687.jpg (http://www.flickr.com/photos/25239206@N06/5557104315/)
IMGP9189 (http://www.flickr.com/photos/25239206@N06/5557104315/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), on Flickr


Up close showing the style of the sprocket and the electrical contact, notice the single bigger ball on the chain just clear of the sprocket and to the right of it.http://farm6.static.flickr.com/5254/5557104233_28e5f8514c.jpg (http://www.flickr.com/photos/25239206@N06/5557104233/)
IMGP9190 (http://www.flickr.com/photos/25239206@N06/5557104233/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), on Flickr

aostling
03-25-2011, 02:01 PM
I recommend "Geared to the Stars" as the best orrery book I know of. It should have some date mechanisms.


Jeff,

I had a look at this book when I was in the library this morning. The book is mostly historical in its treatment of orreries, with many photos of the best specimens found in museums. There are several diagrams too, as shown below. It is not a "how to" book or a technical treatise of the mechanics involved, but it should be an inspiration to anybody contemplating building an orrery.


http://i168.photobucket.com/albums/u183/aostling/GearedtotheStars.jpg

JoeLee
03-25-2011, 02:30 PM
I have a calendar............ it's pretty accurate, has no moving parts and doesn't require any oil or adjustments.

JL................

sansbury
03-25-2011, 02:35 PM
I want to build a calendar like no one else has or has ever seen :D

madwilliamflint
03-25-2011, 02:46 PM
I want to build a calendar like no one else has or has ever seen :D

As we'd say over on Perlmonks: sansbury++

MaxxLagg
03-25-2011, 08:09 PM
Read Neil Stephenson's "The Diamond Age".

You might be refering to his work, "Anathem". That's the one with the clock.

sansbury
03-26-2011, 11:51 AM
As I've pondered this, I've come to the conclusion that an orrery is the wrong mental model for this. The motion of the planets and stars is continuous, while the events I'm thinking about are essentially discrete; digital rather than analog.

Right now I'm thinking of a wheel that's inside another wheel. The outer wheel has 31 catches inside its circumference. Each time the inner wheel rotates, it trips one catch, and that enables the next one. On the 29th, 30th, or whatever-th, it locks the outer wheel so that it makes a full turn with the inner wheel. I got this while looking at the Clock of the Long Now project, which is building a clock designed to run for 10,000 years. They have a patent on their serial adder mechanism, but I think it's pretty different from what I'm thinking of.

http://longnow.org/clock/prototype1/
http://www.google.com/patents/about?id=YMcIAAAAEBAJ

SGW
03-26-2011, 04:52 PM
Thanks for the additional photos of the chain mechanism. It seems as though I ought to be able to come up with some excuse to use that idea, but at the moment I can't imagine what it would be.

Weston Bye
03-26-2011, 05:25 PM
Thanks for the additional photos of the chain mechanism. It seems as though I ought to be able to come up with some excuse to use that idea, but at the moment I can't imagine what it would be.

Did you ever see the movie "Zathura"? The game board used that type of chain to move the player's pieces around.

The Artful Bodger
03-26-2011, 05:34 PM
Did you ever see the movie "Zathura"? The game board used that type of chain to move the player's pieces around.


I believe the very first human powered aircraft use chains of the same style to drive the propeller. The same style, not exactly the same, the ones in the flying machine were made of synthetic material.