I don’t know if it counts as an “implementation” of an FEP control system but a paper by Baltieri, M., Buckley, C. L. , & Bruineberg, J (2020) entitled “Predictions in the eye of the beholder: an active inference account of Watt governors” describes what they admit is basically a “metaphorical” FEP analysis of a Watt governor (a speed control system). They also do a “conventional” analysis of the Watt governor. I think both analyses are inconsistent with PCT since they come to what I think is an incorrect identification of what in PCT is the governor’s controlled perceptual variable and reference signal. I’d be interested in what others think of it.
Best, Rick
PS: There was apparently already a discussion of the Baltieri et al paper here on this forum. I think my conclusion that g is the reference and centifugale force is the controlled perceptual variable is wrong. But not that far wrong. Someone who knows physics better than I do should check this out but I think the reference is the variable “spring constant” force, S.F, of the spring that is lifted or lowered by the centrifugal force, C.F, of the spinning fly balls. S.F, which corresponds to the perceptual signal that is the analog of engine speed. S.F can be varied by varying the length (compression) of the spring,thus changing the C.F (and hence, the speed of the engine) required for the system to reach equilibrium, which happens when C.F = S.F.