## 2 Materials and Methods
### Finite Element Analyses
In detail, the external part with the protective function was to be fixed to the cow's foreleg; while the inner one, which was used to house the mainboard and the battery, was decided to be removable and interchangeable (Figure 11). The assembly of the prototype was designed to obtain a battery compartment, a mainboard compartment and a compartment for the battery charging terminal. The bottom of the inner case, in the battery compartment, has a hole for the passage of the battery terminal connector (Figure 13). \begin{table}
\begin{tabular}{l l l l l} \hline \hline  & \begin{tabular}{l} **External** \\ **Casing** \\ \end{tabular} & \
\begin{tabular}{l} **Inner Casing** \\ **(Central Body)** \\ \end{tabular} &
\begin{tabular}{l} **Top** \\ **Cap** \\ \end{tabular} & **Assembly** \\ \hline External & & & & 55 (Upper part) \\ diameter [mm] & 1 & 45 & 45 & 51 (Central body) \\ Thickness [mm] & 3 & 3 & 10 & - \\ Length [mm] & 95 & 80 & - & 110 \\ Thread [mm] & & M45 \(\times\) 4.5 * & M39 \(\times\) 4 ** & \\ \hline \hline \multicolumn{4}{l}{**Separator**} \\ \hline Thickness [mm] & 1.5 & & & \\ Length [mm] & 50 & & & \\ \hline \hline \end{tabular}  
* *Srewing to the external casing; **Screwing to the inner casing.  
\end{table} 
Table 1: Main geometrical dimensions of double-casing pedometer (Reproduced from [24] with permission from Springer Nature Switzerland AG). Figure 10: Set of pedometer prototypes. Figure 11: Double-casing assembly. Figure 12: Cap of the external case. Figure 13: Cap of the inner case. The printing of this final version of the pedometer was carried out by FDM and performed by a high-quality and high-performance 3D printer: Ultimaker S5 Pro Bundle. The high quality and performance of this printer are ensured by the following technical characteristics:  
* Double extrusion ready for composites;
* Filtering capacity of ultrafine particles equal to 95%;
* Storage of the reels of material with controlled humidity;
* Compatibility with over 90 materials. Once the battery and mainboard were connected and housed in the inner case, the entire compartment was filled with a special bi-component gel with very high dielectric and thermal characteristics (Magic Gel 1000 Ray Tech, Settimo Milanese, Italy). Such a gel, commonly applied to connection systems (joint shells or enclosures) for power cables is aimed at minimizing both the risk of accidental inner disconnections in the electronic circuit and unwanted corrosion phenomena. Table 1 shows the main geometrical dimensions of the prototype components, assumed based on the battery and mainboard sizing. The double-casing design proposed in this paper makes it possible to remove the inner case from the monitored cow after the pregnancy diagnosis. After recharging the battery, the inner case can be plugged into another external case attached to the leg of another cow that would be monitored for oestrus onset. This solution drastically reduces the number of pedometers to be used in a dairy farm. As an example, in a typical barn of 100 cows with an average oestrus window of 22 days and considering that the average period of oestrus is about 18 h, the average number of cows simultaneously in oestrus is 3.5. Therefore, to identify the oestrus cycle in time, it will be necessary to attach the pedometer to those cows that are believed to be close to oestrus, which is equal to about ten. This means that, by adopting the concept of double-casing, it will be sufficient to purchase just 10 devices, i.e., 10 inner cases, to be exchanged between the cows according to their oestrus cycle, in contrast to the purchase of 100 units of commercial pedometers. At the same unit cost, it is logical to foresee an overall average savings of 90% on the company purchase of pedometers (net of the negligible cost of external case, without onboard electronics and equal to the total number of cows).