Celestial train demonstration drive, the orrery dual speed transmission - September 2013                        

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This month we begin to fabricate the drive needed to manually demonstrate the various celestial functions of the clock in both forward and reverse. This drive is actually a small manual transmission, complete with clutches and transmission wheel sliding assemblies. What I wanted to accomplish with this was to have a two speed drive. The first speed, call it "slow", operates all of the celestial functions simultaneously. These contain a very wide span of time reference. The shortest duration functions are associated with he perpetual calendar (the day and date), and the planisphere, (rotating once per day). Next are midlevel durations (the phase of moon, seasonal changes of sun rising and setting, the moon's rising and setting. On the calendar there is the month and season, year, and leap year. Then there is the entire tellurian with earth/moon and sun system which has a one year cycle. The last are the long duration cycles as represented within the orrery which has the outer planets of Mars, Jupiter and Saturn; each having cycles of 687 days, 11.86 and 29.42 years. The ratio between the daily cycle and the longest duration cycle is 10,750:1.

Demonstrating everything together means that some of what is shown in the orrery is moving quite slowly. So we introduce a second speed. This runs at a 12:1 ratio. However, at this speed we would easily 'overdrive' all of the shorter duration cycles. So we disconnect those shorter duration functions; leaving only the orrery driven by this speed of the drive. The transmission has three settings. Normal, that is the demonstration drive is disengaged, slow and fast. We replace the conventional stick shift lever of a car transmission with a push/pull selector operation to manipulate the five clutches and seven gears in this transmission. These wheel counts do not include the external wheels necessary to carry the demonstration power to the orrery.

As is the case with many other aspects of this project the actual design of each system that Buchanan is ready to fabricate is made 'on the fly' just before manufacture. It still amazes me how Buchanan can continue to avoid fatal mistakes in component placement conflicts, or fatal design errors that are ever present in a machine that continues to grow organically in design and complexity from year to year. But as one will see, the space has been all preplanned in the mind of the maker years earlier even if it had never actually been designed on paper (see last photo dated April 2009). Below I've devoted some space to show how the design for this system evolves from a mere thought-schematic, to rough draft and finally a build drawing. 

These four drawings show the initial design concepts. The first drawing depict the wheel and pinion ratios that are present and then those that are desired from the drive. The next three are the physical form that these might take.

Here the design further crystallizes. In the second photo the design is at the point where the individual clutches and the wheel counts begin to come into play. Notice the truth table in the lower half of the drawing. The table indicates which parts of the transmission are engaged or disengaged at each speed, as well as which celestial functions are engaged at each speed.

Now the design begins to take on the precision of a design drawing. The second drawing shows the transmission end-on from the front elevation of the clock.

Here we have a full fledged 'build drawing'. A cutaway of the ball clutches are shown as well as all wheel works in their correct profiles. Note that the truth table has had to be expanded to accommodate additional complications in the design.

Now we have a close up of the prior drawing after all of the dimensions needed to machine the actual parts are penciled in. Anyone who has been involved in the creation of complex structures or the building of model engines can appreciate the intricacies involved in this type of design drawing. It requires a different skill set from those needed in conventional clockwork.

The first two photos show the inner shaft and the sleeve it goes into. The circular profiles on the shaft and holes in the sleeve will later serve as guides for the ball bearing clutch work.  

Various parts being made for the demonstration drive, mostly the gears.

The first photo shows an exploded version of the transmission shaft. Most but not not all components are shown, the ball clutch work is not yet made. The second photo shows most of the gears in the transmission. There is another complete set of wheel works that come later to connect this component with the orrery. 

The transmission shaft and its related components is installed into the movement to test for fit and functionality. As noted at the start of this installment, Buchanan has planned for this drive long before and we can see a shaft exactly where it is now positioned within the movement as shown in the next photo taken in April 2009.

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