Last modified: 2024-09-16 22:27:38
< 2024-09-14 2024-09-17 >I found Aaron Crane's original 1841 patent for the torsion pendulum clock.
Google has it as "Method oe cowstettctiitg clocks", at https://patents.google.com/patent/US1973A/en
I've copied the PDF to https://incoherency.co.uk/interest/US1973-method-of-constructing-clocks-aaron-crane.pdf
The escapement looks very weird indeed.
OK, I've just read the description. This is a most convoluted mechanism. I like it!
The part labelled "F" is a lever sticking out of the suspension spring sideways. It has a pivot in it for a rod, marked H. And then the anchor (G) is a bit like a grasshopper escapement, the pallets (labelled J and I, but I think this is an error, they should both be J) are spring-loaded to move to the left of this pic, but presumably have some sort of stop to prevent them going too far (maybe?).
And then the other part marked H on the anchor takes the other end of the rod. The rod moves left and right a bit, and the left end of the rod moves in and out of the plane of the page, as the suspension spring rotates.
So the overall effect is that the ball is being pushed left and right and is spinning round and round.
Crane makes great claims about the performance of this mechanism, claiming that a suspension spring 3x as wide as its thickness is completely immune to temperature variations, because any increase in its length is adequately countered by an increase in its width. Interesting idea, and obviously those effects both go in the correct direction to cancel each other out, but it seems too much of a stretch to claim that they actually do cancel each other out.
The hook-shaped device labelled N and O is a bodge ("corrector") meant to press against the ball if it is swinging too far.
He doesn't say so, but it sounds like you want the natural frequency of the ball to be equal in its torsional mode to its pendulum mode, otherwise it's going to want to behave weirdly, I suspect. (Or, due to https://www.youtube.com/watch?v=MUJmKl7QfDU - perhaps you want the exact opposite?)
This video shows an Aaron Crane clock escapement: https://www.youtube.com/watch?v=9iZ3ei7Rh60
From 0:07 to 1:04 (front view): the escape wheel is the ratchet-toothed wheel in the centre of the frame, just behind the front plate. The pallets are at its right-hand side, just visible through the gap in the plate. From 1:12 onwards (side view), the pallets are the brass arms at the left-hand edge of our view of the clock, near the front plate, underneath the winding drum.
So now we have a few options: