# Charging Platform of Chess-Pad Configuration for Unmanned Aerial Vehicle (UAV)
## 3 Charging System Design  
### Onboard Charging Circuit Designed (Polarity Modulator Circuit)  
The diode bridge rectifier works like a one-way valve, only letting the positive or negative charge through depending on how they are wired [42]. The two-input terminal of the diode bridge rectifiers is connected to the contact pins; the electric flow happens when these pins touch the charging platform, which is supplied by a DC power source consisting of negative and positive charging signals distributed on the platform plates.  
The significant advantage of this design is the ability to resolve the misalignment caused by landing problems. This feature is critical in drone applications at reduced landing precision when depending on the landing and positioning support systems' performance. The onboard electronic circuit design was configured to minimize the component weights and to decrease design complications and cost. The charging voltage for the UAV battery was regulated on the supply side to match the battery specification and save weight and size for the onboard charging circuit. Figure 2(a) shows the circuit in non-operational mode. Figure 2(b) shows the polarity circuit with four contact pins in operation and providing different charging signals. The (+) symbol represents the charging signal when the onboard pin touches a positive charge tile, but the (-) symbol represent the negative charging signal when the onboard pin touches the negative charge tile. In this case, all the bridge rectifiers are operational and modulating the polarities, as needed for the battery. As shown in the circuit diagram, the diodes circuits use a bold color. This diagram shows the power signal flows through the bridge rectifiers until it reaches the main terminals that feed the battery. Therefore, the inactive diodes are shown in a transparent color, which gives the notion of an off activity. Figure 2(c) shows two contact pins that are active and in contact to the charging pad tiles, thus providing two different charging polarities to the circuit design, while the other pins are considered out of range or not connected to any of those copper tiles; five bridge rectifiers are active and modulating the signal as needed for the battery. Figure 2(d) shows three active contact pins while the others are out of range, and, as previously seen, the charging circuit modulates the signal while improving its modulation. As discussed in the section above, the 16 copper plates can be represented mathematically with standard logical truth tables with \(2^{4}\) different cases. However, the logical truth table cannot express real case scenarios with the UAV landing for charging at different angles and orientations. Therefore, a simulation of randomly landing in 16 cases is illustrated in Table 1, which shows the probabilities of charging as: \"+,\" which represents a positive signal, \"-,\" which represents a negative signal, and \"0,\" which represents a case when the pin either falls out of range when the UAV lands or falls between the isolation gaps between the copper plates, which is indicated as \"null\".  
Figure 2: Lab test for the configuration of the chess pad charging platform.  
Figure 3: The proposed on-board circuit with a contacted sample of the circuit with all connections which diode bridge rectifiers (BR1, BR2, BR3, BR4, BR5, BR6) connected to four contact pin (A, B, C, D) and have four example of operation cases represented in (**a**), two positive and two negatives in (**b**), one positive, one negative, and two disconnected in (**c**), one positive, two negatives, and one disconnected in (**d**).