However, the complexity of the assembly and lack of orientation lock of the UAV are factors that need to be considered. This design can accommodate a wide range of UAV sizes with simple control. Lastly, an innovative design based on “Iris diaphragm” was developed in. In this design, the mechanism can be easily activated by simple rotation, but the fixing of the UAV is looser than the previously mentioned parallel and w-shaped positioning mechanisms. Another type of active positioning mechanism is “Rotating positioner”, which aligns the UAV by means of rotating the legs around. The disadvantages are that it cannot freely adjust the final UAV position other than the center and there is a lack of a clear design guideline for the w-shaped plates. In addition, the electrical contacts can be installed at the inner corners of the w-shaped plate, allowing wired charging and data transfer if needed. The advantage of this method is that it only requires a single actuator to operate. As the two positioning plates clamp in, the UAV is positioned in the center position as it slides along the “V or W-shaped walls” of the positioning plates. In, a w-shaped centering system for the positioning of a quadrotor was developed. Several studies were conducted to improve those multipushing mechanisms to reduce the number of pushers.
Moreover, a special control scheme is needed if the UAV has nonsymmetrical leg structure, such as a non-even number of legs. On the other hand, it requires two actuators to activate. The importance of using this kind of positioning mechanism is that it can be used for a wide range of UAV sizes and the final position is not limited to just the center but is also adjustable by control of the parallel plates. In, an autonomous parallel position mechanism was used to position the UAV to the center position by activating the pushers synchronously. Many positioning, charging, and swapping systems have been suggested and will be reviewed in detail in the literature review section. Usually, the swapping stations require the UAV to land with higher accuracy and therefore need a positioning system to help align and immobilize the drone during the swap. For automatic battery-swapping stations, after the UAV lands, the UAV is positioned in a manner that a robotic gripper can be used to properly swap out the used battery with a fully charged one. In some cases, in-air charging facilities which use Photo Voltaic (PV) cells were attached to the UAV.
A battery-charging station can be a wireless charging system or a wired charging dock to charge the installed battery after the UAV lands on the docking station. To solve the insufficient power issues of the UAVs, several battery-charging stations or battery-swapping stations have been proposed. Battery swapping will take significantly less time than charging at the cost of a usually tedious manual operation and the need for more battery units in reserve. So, the mission time will be directly affected if the batteries of the drones need to charged every 30 min. Generally, it is known that charging a Li-Po battery will take around 1–2 h. These types of batteries usually provide a maximum of 30 min charge for a single drone cycle, depending on the specifications of the drones, sensors and actuators. Nowadays, most of the industries using drones use Li-Po batteries. This is due to the battery power of the drone, as it cannot provide enough power to contribute to longer-length missions such as surveillance, wildlife monitoring, and remote GIS applications. The flight time of Unmanned Aerial Vehicles (UAVs) becomes a major issue when considering the drawbacks of drones. Finally the advantages and the limitations of the system are discussed. A ‘DJI TELLO’ small-scale quadrotor was chosen as a case study to demonstrate the proposed research. A mathematical model and design guideline have been proposed, and a Finite Element Analysis (FEA) was performed to check that the developed platform is strong enough to withstand the above task. The proposed design allows the quadrotor to carry the load under the quadrotor and remain attached throughout the servicing period. The proposed design consist of a docking station, a positioning system and gripper mechanisms. This research presents the novel concept of an Inverted Docking Station that allows a quadrotor UAV to attach to the ceiling during the automatic battery-swapping process. Nowadays, several automatic battery swapping systems are catching interest in research. Once the battery has depleted, the UAV has to land on the ground and human interaction is needed to change the battery with a fully charged one. “Flight Time” and the “Scope of the mission” play major roles in using UAVs as they affect most industrial activities.