What are the units for the SpringJoint’s “frequency” and “damping”. Currently seems like a guessing game. Also what are the units returned when the GetReactionForce function is called?
About rates, what is the physics FPS, and is there any way to increase it, or do “Solver iterations” increase it?
Im not sure about the units. Ive heard in the past about rigidbodys units such as mass just being relative to other rigidbodies (Game Units to Real Units? - Unity Engine - Unity Discussions)
In regards to the physics FPS, I assume you mean the fixedtimestep, which can be found at edit → project settings → time → fixedtimestep
By default it is at .02 (1/.02 = 50 times per second)
You can put it at .01 for 100 times per second as an example.