# Charging Platform of Chess-Pad Configuration for Unmanned Aerial Vehicle (UAV)
## 5 Results
### Charging Performance  
A DC power supply was used to simulate the standard commercial power supply. The configurations for the supply power were set based on the charger manufacturer's specifications. The drone battery is a rechargeable, 2700 mAh, high-density, lithium-ion polymer. Briefly, the range of charger output current was limited to (1.2 A). The charging current was set to 0.27 A, and charging voltage was set to 13 V. However, the battery capacity for input power was set to 12.4 V. Tests were conducted to assess the direct contact method's reliability for charging the onboard drone battery. The outcome of these attempts confirmed the presented method, as the current was found to flow from the power supply to the battery through the chessboard and the onboard contacts once the drone touched the charging platform. Figure 7 shows that the initial charge started at 0.279 A and gradually reduced over time due to Ohm's law. Furthermore, the battery voltage started at the point of the minimum battery cut-off threshold, which was the point that the battery was considered fully discharged. The standard in the experimented battery was 10.4 V, and it rose over time to an open circuit voltage of 12.4 V, which was the maximum potential difference when there was no current that could flow through the battery cells. Figure 6: Simulation results regarding four contact pins: 2 positives (A, C) and two negatives (B, D). Figure 7: The current supply and battery voltage during charging. The charging process depends on the battery's state of charge, the type of power source, and the weather conditions. Upon automatic drone landing, the onboard battery can reach full charge in approximately 180 min. For an analysis of the direct contact and the efficiency of the polarity modulator circuit, the supply voltage was adjusted to 13.7 V and the onboard circuit output voltage (which is the final input voltage for the battery) was adjusted to fit with the 13 V while considering the value of \(\text{R}_{\text{Load}}\) for the copper plate and the polarity modulator circuit, which was 50 \(\Omega\). The following calculation is for the difference between the \(\text{I}_{\text{in}}\) (input current supply) and the \(\text{I}_{\text{out}}\) (output current) of the circuit:  
\[\text{I}_{\text{out}}=\ \frac{\text{V}_{\text{out}}}{\text{R}_{\text{Load}}}\]  
where \(\text{I}_{\text{out}}=0.26\) A. therefore, moving forward with the calculation of efficiency, the charging circuit with a starting input current (\(\text{I}_{\text{in}}\)) of 0.279 A was calculated to be 88.42%. The efficiency of the charging system was calculated using the ratio of the power out from the circuit to the power generated by the DC power supply as follows:  
\[\eta=\frac{\text{V}_{\text{out}}\ \times\text{I}_{\text{out}}}{\text{V}_{\text{in }}\times\text{I}_{\text{in}}}\ \%\]  
where \(\eta\) is the charging efficiency in percent, \(\text{V}_{\text{out}}\) is the output voltage (circuit), \(\text{I}_{\text{out}}\) is the output current (circuit), \(\text{V}_{\text{in}}\) is the input voltage supply, and \(\text{I}_{\text{in}}\) is the input current supply. Table 2 shows that the proposed method's efficiency was estimated to reach 88.42% at the start of charging, as illustrated in Figure 6, by using the power efficiency equation shown above. Compared to related work that has mostly used wireless charging methods, this method was found to have a superior charging performance. It was clear that the maximum efficiency was attained when the onboard battery reached its approximate full charge value; this explained the potential losses of the direct contact recharging process. The losses can be classified as follows:  
* Contact losses due to the quality of the spring contact pins, copper plates, and wires. Their quality can be improved through the use of better materials such as carbon brushes and through the enlargement of the wires' cross-section area.