**5. Conclusions**

In the paper, the mechanical architecture of old watermills of Piedmont (Italy) is presented. Beyond the historical value of the work, the authors believe that the knowledge of the functional details of solutions used in the past allows us to fully understand their potential. They can also permit a full recovery of original tasks, as in the case of the Riviera mill, stimulate the design of new hybrid solutions, or inspire original and renewed uses. Old water wheels, for example, when for economic reasons are not suitable for direct actuation of the original machines, could sometimes be renovated for the production of electricity (micro hydropower generators). In fact, these machines present, in general, an interesting efficiency, between 70% and 85% (See Table 1). In particular, both the water wheels taken as example in this study have a good efficiency, close to 80%, and their restoration or reuse is therefore widely justifiable.

In all cases, for the sake of completeness, to the hydraulic study of the wheel a complete analysis of the mill must be added. In particular, it is necessary: (i) To go into the details of mechanical transmission, (ii) improve some mechanisms that are not very effective, (iii) evaluate the production potential, (iv) model or measure the torque and power characteristics of the whole transmission.

It is not always possible to accurately model the performance of the entire transmission. Water wheels, wooden gears, lubricated plain bearings have an intrinsically non-linear behavior, so that the uncertainty in determining the total efficiency of an old water mill can be significant.

In order to overcome this issue, it can therefore be useful, in perspective, to develop equipment aimed at the in situ experimental measurement of the mechanical characteristic of a water wheel and power transmission, and the definition of its overall efficiency. The portable device should consist of: (i) A unit for the connection with a mill power transmission; (ii) a braking unit capable of generating the load torque; (iii) a measurement unit, appropriately instrumented to determine the torque and power characteristic as a function of the rotation speed of the load shaft.

**Author Contributions:** Conceptualization, W.F., C.F. and R.R.; Methodology, W.F., C.F. and R.R.; Investigation, W.F.; Writing—original draft preparation, W.F.; Writing—review and editing, C.F. and R.R.

**Funding:** This research received no external funding.

**Acknowledgments:** Authors would like to thank the Cavanna family, owner of the Riviera mill, for their willingness, Davide Massucco for having carried out the survey of the Riviera mill and Paolo Cavagnero for some pictures of both mills.

**Conflicts of Interest:** The authors declare no conflict of interest.
