These are my posts sharing the story and CAD files for my (first) recreation of the Antikythera Mechanism. My second version is in-work, pending completion of my Lasersaur to help with prototyping.
Update June 2015: I’m revisiting this project to finally get it to a version where it can be manufactured at home. Check greekgears.com for future updates.
The Antikythera Mechanism is the world’s first known mechanical computer, used by ancient Greeks to predict the path of planets in the sky, the dates of eclipses, lunar phases, and several religious calendars. It was made sometime around 100BC, and it was not until a thousand years later that anything rivaling its complexity was found. Before its discovery we had no idea the Greeks had technology anywhere near this sophisticated.
For a CAD class this semester, I reconstructed the Antikythera Mechanism as a 3D model in Solidworks. It’s to scale, and it works! Watch the video to see it in action, and turn on annotations for a description. Alternatively, download the CAD files for yourself.
The video goes pretty quickly, so I’ll show some pictures of the key features below.
The front face is a planetary display. Pointers track the position of the 5 planets known to the Greeks, the sun, and the moon, all as observed from Earth. These pointers track along the inner ring, which displays the zodiac (the position of each object in the sky). Because of the different speeds of these orbits, some of the planets experience apparent retrograde motion, and capturing this epicycle motion is the reason for much of the complex gearing system. The front also displays the date, which tracks along the 12-months outer ring. At the center of it all is a ball representing the moon, painted black on one side and white on the other. This rotates to show the moon’s phase on any given date – black for a new moon and white for a full moon, with everything in between. You can see this in the video pretty clearly.
The back face is a calendar display. The top half tracks the Metonic Cycle (19 years) and the Callypic Cycle (76 years), which form the basis of the Greek calendar. It also tracks the cycle of the Olympic Games (every 4 years). The bottom half tracks the Saros Cycle (223 lunar months), and the Exeligmos Cycle (669 lunar months), which can be used to predict solar and lunar eclipses! Scientific American has a great infographic on how to use the Antikythera Mechanism to predict an eclipse.
How does it all fit together inside? Well, during my research I found that there wasn’t a complete picture of how the gears were all related. There was a good picture for the bottom half, but the rest had to be cobbled together from several different places. So to help me visualize it while working on the project, I drew up a map of how everything fit together. And because I had some free time yesterday, I cleaned it up and put together this infographic to make it all clear (it’s on wikipedia now so it doesn’t get lost). It’s pretty self-explanatory, and hopefully it will be helpful if anyone in the future wants to make their own reconstruction.
I’m pretty awestruck, to be honest, that someone was able to make this over 2000 years ago. Even though it was built during the time of Rome’s peak ascendency, it is so many levels above any other technology we have from that day that it seems almost anachronistic. I had enough issues coming to understand the complexity and detail that is packed into this small box, and I already knew how it was going to work! It makes you wonder what other marvels were created that have been lost to time.
“This device is just extraordinary, the only thing of its kind. The design is beautiful, the astronomy is exactly right. The way the mechanics are designed just makes your jaw drop. Whoever has done this has done it extremely carefully … in terms of historic and scarcity value, I have to regard this mechanism as being more valuable than the Mona Lisa.”
– Professor Michael Edmunds, as quoted in The Guardian
I’ll close off with a list of the papers I used. The first Freeth paper was by far the most helpful, and I might have been able to make it based off of just that paper alone. The others were helpful for context and comparison though. And this youtube video, even though it was for a different gearing schema than the one I used, was helpful in wrapping my head around how it would go together.
Evans, James, et al. “Solar Anomaly and Planetary Displays in the Antikythera Mechanism.” Journal of the History of Astronomy 61 (2010)
Freeth, Tony, and Alexander Jones. The Cosmos in the Antikythera Mechanism. Institute for the Study of the Ancient World, 2012.
Freet, Tony, et al. “Calendars with Olympiad display and eclipse prediction on the Antikythera Mechanism.” Nature 454 (2008): 614-617
Freeth, Tony, et al. “Decoding the ancient Greek astronomical calculator known as the Antikythera Mechanism.” Nature 444 (2006): 587-591.
Wright, Michael T. “The Antikythera Mechanism: A new gearing scheme.” Bull. Sci. Instrum. Soc 85 (2005): 2-7.
Update June 2015: I’m revisiting this project to finally get it to a version where it can be manufactured at home. Check greekgears.com for future updates. I have also withdrawn the files and re-released them under a similar noncommercial license.
Update June 2016: Haven’t forgotten about this project, but I’m back in grad school so free time is limited. I’ve gotten it to a point where I’ll need a laser cutter to test out design options, so things are pending me finding one I can get.
By request, I’m making the CAD files for the model of the Antikythera Mechanism that I created freely available. (Click that link for an overview of the project.)
Download the Antikythera Mechanism from Google Drive here. You’ll need Solidworks to open it, and 3D PRINTING WILL PROBABLY NOT WORK. I’ve gotten asked that a lot.
It isn’t perfect. There are a few issues that would keep it from working if you 3D printed this, and a few more issues that make it not completely authentic to the original Mechanism. Here are the places where the model differs from the Antikythera Mechanism. Italicized issues keep it from working if it was 3D printed. I estimate it would take me 40-50 hours to fix them (it would require a redo of a lot of parts), which I don’t really have time for right now. But… if someone had access to a 3D printer and would print me a copy pro bono, I might be motivated enough to clean it up.
- All gears except for the lunar phase geartrain are assumed to have a module of 0.5. This is actually the mean value of the modules for all gears in the Mechanism. A more accurate model would account for variations in the gears. In one instance, this creates a collision between a gear and a support as it travels around. A few gears should also be thicker.
- I didn’t use values for the pin placement radii on the epicycle gears. These can be found in Freeth and Jones’ “The Cosmos in the Antikythera Mechanism.”
- Two indicators should slide onto the Metonic and Saros pointers, and track in the engraved spiral on the back face. Solidworks had issues with a tangent relationship to a spiral, so these are suppressed in the model (but are still there!).
- The Antikythera Mechanism used a combination of adhesives, pins, and friction fits as fasteners. The model uses no fasteners, and would need a few if printed. All the gears that need to have locked rotations are keyed and spaced out with spacers, but some of the keys are really small loose pieces and should be changed.
- There are no tolerances built into this model.
- The Antikythera Mechanism used triangular teeth. The model uses involute profiles. Solidworks was having issues creating these profiles in a couple cases, and a few gears don’t mesh correctly.
- The wooden frame, pointers, and posts are creative interpretations. The large pointers should be removable in the real model to allow the indicators to reset.
- The planet positions are not zeroed to any celestial day.
Despite these differences, the form, function, and essence of the Antikythera Mechanism remain intact.
Also, some licensing info!
I am releasing this to the public under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence. This is a mouthful, but it basically means that you are free to use, edit, and redistribute these files so long as you a) credit me for originally making them, b) don’t use them to make money, and c) apply the same license whenever you redistribute it. This means they will be forever free. With the following exceptions!
- The files “plate back lower dial v4.png” and “plate back upper dial v4.png” are taken from Freeth et al. “Calendars with Olympiad and Eclipse Prediction on the Antikythera Mechanism: Supplementary Notes”, and slightly edited by me. Copyright belongs to original owners, however because it is a published paper all educational uses are fair use.
- The file “plate front v2.png” is taken from this image, originally made by J. Evans and A. Thorndike, and edited by me. Copyright belongs to original owners. (They might mind if you use it educationally. I doubt it though.)