## 3 Results
### Materials and Devices Used in the Implementation of Test Stands
#### 3.1.1 Prototyping of the Expandable Prosthetic Module  
In Figure 3, the final construction variant of the EPM for lower-limb prostheses is illustrated. It consists of a mobile prosthetic assembly (1) and a fixed prosthetic assembly (2), positioned between a socket for residual limb support and the artificial ankle joint, which can be either active or passive.  
It was observed that the mobile prosthetic assembly (1) contains a pyramidal adapter with a screw-based fixation system, allowing it to connect with the standardized pyramidal systems attached to commercial prostheses. The adapter partially houses a flange that rests on it, into which a casing with a shoulder is screwed. This casing supports another casing, which is also fixed by screwing. The fixed prosthetic assembly (2) consists of a flange into which the casing is inserted and fixed into a pyramidal adapter identical to the one in the mobile assembly. This adapter attaches the prosthetic socket or the osteointegrated implant at the patient's residual limb level using standardized fixation elements. The fixed assembly also contains a DC motor, which operates a screw-nut mechanism that converts rotational motion into linear motion.  
We used a 12 V CHR-GM25-370 DC motor to drive the EPM, which has the technical specifications listed in Table 1.  
In this iteration of the prototype, the EPM was modified to enhance its robustness. The prototype was found to have a weight of 680 g. It is hypothesized that, for a prototype intended for clinical testing, the weight can be significantly reduced through the optimization and refinement of components.  
Figure 3: The CAD version of the expandable prosthetic module with the two assemblies (1—mobile prosthetic assembly; 2—fixed prosthetic assembly).  
In order to simulate the most realistic conditions for testing the EPM, we selected an anatomically shaped mannequin on which intervention was performed by sectioning the left lower leg. This simulates laboratory conditions similar to those of a patient with a transtibial amputation (Figure 4).  
In accordance with the standardized dimensions in the field of prosthetics, two pyramid-shaped elements were made and attached to the extremities of the extensible prosthetic module (EPM). These components enabled the integration of the EPM into the mannequin, which was positioned in a seated position on a rigid chair, with the shins oriented approximately perpendicular to the base plate that supported the feet. Both feet  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Technical Specifications** \\ \hline Construction & Permanent magnet \\ Torque & Maximum 5 kg\(\cdot\)cm \\ \hline Type & Micro Motor \\ \hline Commutation & Brush \\ \hline Efficiency & IE 2 (High efficiency—according to IEC 60034-30-1 [31]) \\ \hline Diameter & 25 mm \\ \hline Shaft length & 8 mm \\ \hline Shaft diameter & 4 mm, D-type shaft \\ \hline Supply voltage & 12 V DC \\ \hline RPM & 15 \\ \hline Weight & 100 g \\ \hline \hline \end{tabular}
\end{table}
Table 1: The technical characteristics of the CHR-GM25-370-12 V DC motor [30].  
Figure 4: Anterior-lateral view of the EPM attached to the anatomical mannequin.  
were fixed using fastening devices, ensuring stable connection to the base plate and precise alignment of the forming elements.  
The EPM components are fabricated from robust materials, with a weight capacity of approximately 70 daN. It is important to note that the prosthesis does not correct LLD under the weight of the entire body or the affected side of the body. Adjustment of the prosthetic length takes place when the subject is in a seated position, so the load on the EPM is minimal. In the unlikely event of additional motor power being required, the EPM's modular design allows for the replacement of the motor with a more powerful one.