Store design experiments

I've mostly adopted Babbage's Plan 27 arrangement for the Mill, including the use of independent columns of pinions for the various meshing: the rack with digit wheels, digit wheels with long pinions, and long pinions with the anticipating carriage.

But is is appealing for the Store to use a simplification that he introduced in Plan 28: to engage the digit wheels by lifting, rather than with separate columns of pinions. That not only eliminates one of the lifting motions, but also two rotating motions for locking the digit wheels, since their vertical motion can lock them to fixed fingers on the frame. 

The store wheels are duplicated many times, so having only two independent motions -- lift for meshing, and finger rotation for giving-off -- instead of five is a huge advantage. It is unfortunately not possible to do this in the Plan 27 Mill because both digit wheels in a "cage" (a pair of wheels representing the same decimal position of two different numbers) are sometimes required to be independently meshed to different things.

I have a small tester working that demonstrates the design for the Store, and for the rack which interfaces with the Mill . The rack is made of separate 12" segments that the 3D printer can make, lapped on the ends so that any number of segments can be bolted together to make a rack long enough to span the entire Store.

The internal wheels that stick out above and below ride in channels in the supports, which constrains the rack both vertically and laterally. Each support serves the top wheel of one cage and the bottom wheel of another cage.

The internal fingers can rotate but are fixed vertically. The wheels can move vertically into one of five positions: 

1. read bottom: up 0.6" to engage the bottom wheel with the rack and the finger with the bottom wheel's nib
2. write bottom: up 0.3" to engage the bottom wheel with the rack, but not with the finger
3. home: neither wheel is engaged with the rack, and both are locked by fingers projecting from the supports.
4. write top: down 0.3" to engage the top wheel with the rack, but not with the finger
5. read top: down 0.6" to engage the top wheel with the rack and the finger with the top wheel's nib.

A wheel not meshed to the rack is always locked ("for free") by the projection on the support, which is neat. The rack itself will need to be locked too, but that can happen in the one special wheel axis that will also serve to restore the rack to its home position after a read or a write. 

That restoring wheel also provides a mechanism to implement both destructive and non-destructive reads, which Lovelace (maybe also Babbage?) invoked via "Zero Supply-cards" and "Retaining Supply-cards", respectively. Doing both is a requirement to be able to execute her published trace for the calculation of Bernoulli numbers. Note that non-destructive reads would have been much harder to implement for designs that had a central wheel, like that shown in the famous Plan 25 drawing.

My tester, like the 4-digit anticipating carriage prototype, temporarily uses 21st century components to effect the finger rotations and wheel lifts.

Here is a video that shows the basic operations:

So far, so good. No doubt problems will arise in scaling it up and connecting it to the Mill.

Incidentally, I've made the gear tooth spacing closer for the Store than the Mill (DP of  8 instead of 6) so that the wheels are smaller (2.5" diameter instead of 3.33") and more of them can be packed in a given space. The conversion between the two spacings can't be done by the rack, since single whole-tooth movements have to be preserved. So the pinion axles in the Mill that connect the rack to its digit wheels will have ganged pinion gears that do it.