# Nano Aerial Vehicles for Tree Pollination
## 3 Proposed Solution
### Power supply
#### 3.1.2 Printed Circuit Board  
For the design of a PCB for a NAB, it is crucial to perform the following steps to minimise the length of the tracks:  
* Determine the PCB structure;
* Study and place the components and define the PCB layout;
* Analyse and make connections between components.  
After defining the NAB schematic, we began work on the PCB design. The shape and dimensions of the PCB are similar to those of the Crazyflie 2.1 to ensure aerodynamics. The board consists of a 30 \(\times\) 30 mm square with some arms at each vertex of 20 \(\times\) 7 mm. As with the AI Deck 1.1, we added a small platform for the NINA-W106 (12.7 \(\times\) 8 mm).  
Board mapping was analysed to minimise track length. In particular, the following constraints in terms of the level of orientation and/or the position of each element on the board were considered:  
* Since the RP2040 is connected to the highest number of components, the microcontroller should be in the centre of the board. Additionally, it is crucial to avoid placing any elements that could interfere with via in the opposite layer.
* The voltage decoupling capacitors must be placed close to the RP2040 power supply pins to reduce noise.
* The NINA-W106 must be in the top layer, given the size and weight of the component.
* The micro USB connector must be on the top layer, closer to the edge, and oriented for easy access.
* The 8-pin connectors must be on the sides of the board. None of these sides must coincide with the micro USB connector.
* Four motors must be at each end of the arms so the corresponding connectors must be at the start (by arms, we mean the rectangular platforms of the board).
* The fifth motor must be on the edge of the board.
* The VL53L1X must be on the bottom layer to measure the distance to the ground.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Component** & **V** & **Imin** & **Pmin** & **Imax** & **Pmax** \\ \hline RP2040 & 3.3 V & 0.18 mA & 0.594 mW & 35.5 mA & 117.15 mW \\ NINA-W106 & 3.3 V & 0.005 mA & 0.0165 mW & 190 mA & 627 mW \\ BMI088 accelerometer & 3.3 V & 0.003 mA & 0.0099 mW & 0.150 mA & 0.495 mW \\ BMII088 gyroscope & 3.3 V & 0.025 mA & 0.0825 mW & 5 mA & 16.5 mW \\ VL53L1X & 3.3 V & 0.003 mA & 0.0099 mW & 18 mA & 59.4 mW \\ LDK130M33R & 0.1 V & - & - & 100 mA & 10 mW \\ BQ24075 & 3.7 V & 0.0043 mA & 0.0159 mW & 1.5 mA & 5.55 mW \\ DC motor & 4.2 V & - & - & 1000 mA & 4200 mW \\ W25Q128V & 3.3 V & 0.001 mA & 0.0033 mW & 25 mA & 82.5 mW \\ \hline LiPo battery & 3.7 V & - & - & 3750 mA & 13.875 mW \\ \hline \hline \end{tabular}
\end{table}
Table 7: Component consumption and power supplied by the LiPo battery.  
* The buttons of the flash memory must be on the top layer for easy access.  
In addition, it is crucial to check the pinout of the RP2040 to place the other components accordingly. A board layout that minimises track length based on the RP2040 pinout was studied, along with the previously mentioned constraints. To ensure the NAB was balanced and the connections between components could be easily made, we carefully considered the weight distribution and orientation of the components when placing them on the PCB.  
Additionally, different track specifications were considered when tracing the connections, namely:  
* For the connections of the microcontroller, it was necessary to use tracks with a width of 9 mil so that there was no contact between pins.
* Most of the links were 10 mil wide.
* The motor tracks were 14 mil wide to facilitate heat dissipation.  
To facilitate communication between the different layers, we utilised vias--small holes that establish electrical connections--between all layers, with a diameter of 24 mil and a drilling diameter of 12 mil.  
Figure 3 shows the components and connections of each layer. The upper and lower layers are the most populated. The wider tracks related to the motors are in the inner 1 layer.  
The development of the NAB's PCB presented many challenges due to the reduced board size that contained many components and increased connections.