Help rotating bone in relation to spinning wheel without keyframes

[DNorman]

I would keep it all in one rig, the end goal is to be able to drive everything with the wheel rotation, the tricky part of these gears is in the combination lever, as it has to combine the movement from the radius rod and the union link with a fixed pivot. The trick is to use a very large upright bone that fixes the pivot point and combines the horizontal movement.
I uploaded a version of the gear here in my last post:

How to rig this piston-like mechanical setup?

Sorry I did not see your post until today. I also came to a similar conclusion as you after watching this video: [Blender Tutorial: Walschaerts Valve Gear Animation] by Locomotivist. I did not use any empties or constraints - only bones and Ik’s. Edit: to get the pivot point of the link sliding I created a third IK system, which points to the center of the radius of the link’s curve that maintains and slides the pivot point in the groove of the link. You can change gear by rotati…

Feel free to download and use but I do recommend you try to understand and replicate the mechanism yourself.
edit:

@GuitarGuy

There’s 3 armatures in all.

Bare in mind that the whole gear is one mechanism and that the valve piston movement is dependent on all the other parts!
Edit 2
To answer your specific question I recommend you start with a drive bone (that will drive the rotation of the wheel). In my file the drive bone is called “driver”, it starts in the centre of the wheel and extends to the eccentric crank, the eccentric crank is a child bone of the drive bone and inherits its rotation. The eccentric rod is a child of the driver bone but does not inherit its rotation. The main rod has an Ik system that uses a child of the eccentric crank as its Ik target.