Hi Steve,
The Dynamic solution would have the need to be very precisely set up in terms of hierarchy with all elements. The first element must be calculated first, then the second, etc. If that logic is not consistent through the chain of actions, I would expect some kind of trouble. If that is for a production, I would make is as safe as possible.
I have attached a scene file with three cogwheels. I used here the smallest element in XPresso to calculate something. The “$1” stand for the input. The negative is needed for every second element to change the rotation direction. Then you can see that I just did the tooth-math.
As any element in a change is dependent on the initial element, I do not create a chain of calculations., to keep it clean.
If you change the R.B. (see image) of the first Null object 9not the cogwheel), then it should work fine.
If you like to do a gear box or a clock, then you find that there are often two cog-wheels connected on one axis, but with different amount of teeth and diameter. This twin wheel that branches the rotation to a new line, is then the starting point of a new XPresso Node, as from there the rotation speed might change. Hence the idea of a gear box to change speed in the first place.
If the chain of elements needs that little imprecision, the gap between the teeth of two elements, a little bit more work is needed, perhaps a memory node to have that established.
I talk here about preparation for animation, for a rendering. There is my target and ideas.
All the best
Sassi
P.S., the file is r15 as I was not certain which version you have already installed.