G'day chris here and welcome back to clickspring
In this video I make the small gearing module that models the ancient Greek understanding of the variable motion of the moon
In modern astronomical terms, there are two components to this variable motion
There's the slight variation in speed as the moon follows what we now understand to be in elliptical orbit
and then there's the slow procession of the axis of that orbit that slightly
Extends the time it takes for the moon to come back to the same place within the orbit itself
this is known as the anomalistic month and
The motion is neatly captured within the gearing of this next part of the mechanism using two separate inputs
The first input is the mean sidereal period of the moon and it drives a gear on the e assembly platform
That is a small pin on its upper face
The pin fits into a small slot on a gear located directly above it and the two rotate together
Ordinarily this would serve no purpose
But the gear with the pin turns on a slightly offset access to that of the gear with the slot
So that as they turn together the slot gear is forced to travel at a variable speed
I've added reference lines to show how the slot gear
Oscillates between being slightly ahead and then slightly behind the driving gear as it goes through each revolution
The slot gear travels fastest when the pin is closest to the axis of rotation and slowest when it's farthest away
With the result being that the mean sidereal period now has a cyclical variation to it
now at the same time the maker contrived a second input to drive the platform upon which these gears are mounted
introducing a second component to the variable motion and
You recall from previous videos that the 53 tooth gear cancelled out of each of the metonic and Sarah strained calculations
that it remains in the calculation for this section of the train and in fact its purpose is now revealed to assist in
Calculating the correct period for the precession of the lunar orbit
By mounting the pin and slot gearing epicyclicly on this platform
The two variable components of the lunar motion are now combined to model the anomalistic month
And as if that wasn't impressive enough the output was then sent via
coaxial shaft back through the input hub and
Handed off to another shaft that drove the lunar phase assembly on the front face of the mechanism
Prior to its discovery amid the antique ether wreckage the classical texts had already suggested that something along these lines
existed in antiquity. For example the account from Cicero
Someone could be argued that the physical evidence of mathematical gearing of some sort should have been expected from the period
But there was nothing on the record to suggest that it would be anything like this
such a sophisticated design modeling an astronomical concept that's hard enough to describe with words let alone gears and
Executed with a technical confidence that can only come from long experience and a deep knowledge of the craft of constructing find mechanism
Which naturally leads to the conclusion that it was the product of a well-established
engineering tradition that was much broader and more capable than had been previously imagined and about which we presently know very little
And that final fact means that it largely falls to the mechanism itself to tell the story
to hint at the tools used and to guide the speculation
about how such a machine might have been created more than two thousand years ago
This small hub forms the basis of the component that I introduced at
the end of the previous video the mean lunar sidereal input assembly
And with the flats formed the holes in the wheels were formed to match
The smaller one to be a permanent fit on the hub and the larger removable to permit disassembly from the e platform
This small assembly rotates on the e Arbor which is the final output of the pin and slot module and at the same time
It's the primary bearing surface for the e platform. So that puts the the Arbor at the center of quite a complex coaxial structure
The various steps shoulders on the Arbor are also responsible for setting vertical clearances throughout this section of the train
All of which makes it one of the most critical components of the machine
This Arbor carries two wheels
The larger one receives the output of the pin and slot mechanism and the smaller one hands off that rotation to the lunar phase shaft
And here's a closer look at how this set of concentric assemblies comes together with the larger e platform components absent to make it easier to view
It's a complex stack of step shoulders and bearing surfaces that all serve to keep the various wheels and assemblies
not only aligned for meshing, but also appropriately separated from each other and so operating at minimum friction
The pin and slot wheels interface directly with this stack of gears and of course need some specific mounting hardware to perform as intended
starting with the eccentric pivot
And with that pivot complete the various components that make up the pin and slot module were brought together to be hand fitted into position
The pivot location on the e platform was determined by depthing the pinwheel with the lunar sidereal input wheel and
Again much like the rest of the mechanism that depth thing can be determined using direct observation and a simple tool
With the depthing of the wheels confirmed the pin and slot features were formed next
The other key pieces of mounting hardware are the lugs and bridge strap that serve to restrain the pin and slot wheels in position
The strap appears to have been bent to shape from a thin section of sheet metal
So I've made a set of simple forming tools that I think could have plausibly been used to shape the part
The retaining lugs were formed in the same way as those used to fasten the e platform together
and the bridge strap was used to identify their position on the e platform
After confirming the fit of the bridge strap the two retaining lugs and the eccentric pivot were permanently fastened into place
The holes for the retaining pins in the e arbor were also formed, the top one being essential to retaining the entire assembly in place
When the machine is inverted
And with that the main components of this complex assembly are complete so here's how it all goes together
This part of the machine is a little unusual in the sense that it can be considered a self-contained module
So unlike most of the mechanism it's performance can be examined that assessed independently from the rest of the machine
Much like a mechanical clock the main challenge at this point is to identify any localized binding of the components
So it's easy to imagine testing like this being carried out on the original device
Checking for freedom of movement and observing the pin and slider operation before it was finally installed within the mechanism
And this brings us to a key moment of the reconstruction
Because for the first time a significant portion of the device can be viewed and operated as a functioning mechanism
As expected the friction has increased due to the nature of the gearing that's been added in this section
But it remains at an acceptable level
the input has a light feel and there's a comfortable free movement of the gearing and
Although there's still a long way to go in this build, the full vision of the maker is now starting to emerge
of a compact mechanical platform upon which then state-of-the-art
astronomical concepts could be represented and combined into a single
all-encompassing
model of the cosmos
Thanks for watching I'll see you later