A Lego Replica of the Antikythera Mechanism

A user writes "The Antikythera Mechanism is the oldest known scientific computer, built in Greece at around 100 BCE. Lost for 2000 years, it was recovered from a shipwreck in 1901. But not until a century later was its purpose understood: an astronomical clock that determines the positions of celestial bodies with extraordinary precision. In 2010, a fully-functional replica out of Lego (YouTube video) was built."

Re:I must have this!!

[JaZz0r]

Andrew Carol is the designer. His website has more information - http://acarol.woz.org/antikythera_mechanism.html [woz.org] If the site is down, try the Google cache [googleusercontent.com]

NOT a replica

[Gravis Zero]

it's an implementation of the same math that that the Antikythera mechanism does but it's done in a completely different fashion.

Woz explains the device on his own page as well as the math behind it: http://acarol.woz.org/antikythera_mechanism.html [woz.org]
There is also an article about his LEGO device: http://www.fastcodesign.com/1662831/how-one-engineer-redesigned-an-ancient-greek-mechanical-computer-out-of-legos [fastcodesign.com]

more information about the Antikythera mechanism can be found here: http://en.wikipedia.org/wiki/Antikythera_mechanism [wikipedia.org]

Re:I must have this!!

[TheMidget]

.... which also shows that it is not a replica of the Antikhera mechanism. It achieves the same purpose (predicting eclipses), but using a different mechanism, because they needed to work with gear ratios achievable with available Lego pieces, and thus needed to add differentials, whereas the Greeks had no such needs (making their own gears, so being able to directly use whatever ratio was needed). Moreover, display differences (4-wind spirals versus 5) introduced more differences in the multiplicative constants, and thus the mechanism:

Because it would be difficult to fit the information for 223 lunar months in a single rotation of a dial, the original machine used a 5 wind spiral to encode the information. This made more space available for the markings required for the eclipse information.

My version of the machine uses a 4 wind spiral. This provides the same benefit as a 5 wind spiral but matches the Full Moon Cycle which may permit future enhancements to accuracy.

This change results in the formula:

Saros4 = Y * 4 * 235 / (223 * 19)

I decided to not use the Corinthian calendar and instead use the standard Gregorian civil calendar in a four wind spiral representing the four year leap year cycle.

Noting that 235 is 5 * 47 and 254 is 2 * 127, the important constants for the construction are:

4, 5, 19, 47, 127, and 223.

The readily available high quality LEGO gear ratios are combinations of 1, 3, and 5. With some challenge 4 is available. With these combinations we can get to gear ratios which are multiplicative combinations of these values. The easy ratios we can get to include: 1, 3, 4, 5, 9, 12, 15, 20, 25, 27, etc.

Ratios of 19, 47, 127, and 223 are impossible to achieve with simple gear ratios because they are prime numbers. We have to look beyond simple gears to differentials.