I added a wrong comment on the One Fact blog, so if you go over there, ignore it. I plead temporary insanity. :-)
+Dan one thing you don’t need to do is model every thing that is occuring in the system, only the things you want to control. The caliper wearing down the rotor is irrelevant to control of the brakes.
If there was a way to dynamically check the thickness of the rotor, then a minimum thickness attribute would probably exist in the model (most likely in a specification class for the rotor rather than the Rotor class. A sensor would also have to be added. If this dynamic sensing isn’t in the system, then the minimum thickness would not be needed in the model, so it would better reside in a service manual.
I’m not sure all of your verb phrases were targeted at additional relationships. The “drives/multiplies torque of” might be considered a better verb phrase for R3, because it helps to illustrate the need for the reduction and torque attributes.
For R2, “closes” is more descriptive than “applies force to”, because “applies force to” doesn’t give a reason. As an additional relationship, it would be redundant.