## 3 Results
### Lifting Energy and Efficiency
The electrical energy consumed (\(E_{el}\)) during each lifting cycle was measured using a high-resolution data acquisition system that recorded voltage and current signals throughout the operation. These signals were subsequently processed and filtered to remove high-frequency transients. This signal conditioning ensured accurate computation of \(E_{el}\), as well as the extraction of representative values of average and median electric lifting power--denoted as \(P_{el\text{-}agg}\) and \(P_{el\text{-}med}\), respectively--derived from the instantaneous power profiles of the lifting motor captured during each test. To assess the relationship between lifting efficiency and electrical behavior, a total of 55 tests were initially considered, as summarized in Table 1. However, two tests (one corresponding to load weight of 1002.5 kg and other to 1100.0 kg) were excluded from the analysis due to their classification as outliers. As a result, the final dataset included  
Figure 8: Detailed energy conversion architecture and measurement points of the lifting system. 53 lifting tests conducted under varying load conditions. For each test, the lifting efficiency was computed as follows:  
\[\eta_{l}=\frac{E_{pl}}{E_{el}} \tag{4}\]  
Table 2 shows the lifting test results, including average and median power (\(P_{el-avg}\) and \(P_{el-med}\), respectively), electrical and potential energy (\(E_{el}\) and \(E_{pl}\), respectively), and calculated lifting efficiency \(\eta_{l}\). Figure 9 shows the lifting efficiency as function of both \(P_{el-avg}\) and \(P_{el-med}\). This figure shows that the lifting efficiency ranges from approximately 7% to 25%, and tends to increase with higher power levels. This trend suggests that, among the different sources of losses, the hydraulic gear pump is the only component whose efficiency can improve with increased power due to reduced relative leakage at higher pressures and speeds [9]. In contrast, losses in the DC motor and mechanical components are generally expected to rise with greater power demand, making their contribution to efficiency relatively constant or decreasing. Therefore, the observed increase in overall efficiency with power is likely driven by the behavior of the hydraulic subsystem under varying load conditions. Two correlation analyses were performed to examine the relationship between lifting efficiency and electrical power demand. Figure 9a shows the results using the mean electrical power \(P_{el-avg}\), where a moderate linear correlation was observed (\(R^{2}=0.756\)). However, as shown in Figure 9b, when the median electrical power \(P_{el-med}\) was used instead, the linear relationship improved significantly (\(R^{2}=0.832\)). These findings suggest that the median power is a more robust indicator of the power demand during lifting, as it is less affected by local fluctuations and transients commonly present in raw power signals. The analysis further reveals that the underlying data distribution is asymmetric, making the median a more reliable measure of central tendency than the mean, which can be skewed by extreme values and thus provide a distorted representation. Figure 9: Dependence of lifting efficiency on the electrical power: (**a**) average lifting power, (**b**) median lifting power.