Gear-train directions, spring winding, and gimbal rings
How coupled wheels reverse or agree, and rings that turn every way
The page works out the directions of rotation in coupled wheels and pinions: with three wheels b, a, c in a line, whichever drives them the two outer wheels always turn the same way; and when a great wheel turns, the little pinions a and n reverse relative to each other while n and m agree, n turning with the great wheel. Other notes describe a ball turned in any direction without moving its center, contrary motions made by m and n, and a pivot turned only to wind a spring that never runs back. Twice Leonardo labels a set of nested rings that turn every way 'like the mariner's compass,' a gimbal, drawn beside gears, a toothed rack and a paddle-wheel with weight. Parts are lettered a, b, c, m and n.
On this page
Three wheels in a row: the outer two always agree
If wheel a turns to the left, wheel b turns to the right, and likewise c turns to the right. Whichever of the three wheels is the cause of the motion, the two outer wheels always turn in the same direction.
Pinions reverse while sharing the great wheel's sense
When the great wheel turns around, the little pinions a and n move in contrary motion to one another. And n and m turn in one single direction, and the great wheel and the little wheel n turn in the same direction.
Rings that turn every way, like a mariner's compass
A manner of circles that turn in every direction, like the mariner's compass, so that a ball may be turned in any direction without turning its center.
A pivot turned only to wind a one-way spring
Here the pivot is turned only to wind the spring, which never returns backward.