C3 System

Drone (UAV) receiver protocols are a crucial part of the drone communication system, defining the data transmission method between the drone receiver and the flight controller. Here are some common UAV receiver protocols:

• PWM (Pulse Width Modulation): This is one of the oldest protocols, transmitting control signals through pulse width.
• PPM (Pulse Position Modulation)**: Also known as CPPM or PPMSUM, PPM signals transmit a series of PWM signals sequentially on the same signal wire, with each channel’s pulse position modulated differently.
• SBUS (Serial Bus): Used by brands like Futaba and FrSky, supporting up to 16 channels over a single signal wire.
• CRSF (Crossfire): Developed by Team Black Sheep, supports two-way communication, including telemetry features.
• IBUS: FlySky’s serial protocol, supporting two-way communication for sending and receiving data.
• XBUS: Used by JR, supporting up to 14 channels over a single signal wire.
• MSP (MultiWii Serial Protocol): Created by the MultiWii software, supporting 8 channels over a single signal wire.
• FPort: Developed by FrSky and Betaflight developers, combines control signals and telemetry data into a single bi-directional signal, eliminating the need for additional UART ports.
• MAVLink: Similar to FrSky’s SmartPort, this telemetry protocol developed by the Pixhawk/ ArduPilot community supports two-way communication.
• DSM2/DSMX: Spektrum’s TX protocols, with DSM2 signals known for their resistance to interference, and DSMX further improved upon DSM2, capable of switching to a new frequency channel within a few milliseconds.
• ACCST: Used for X-series receivers, such as X4R-SB, R-XSR, XM+, and long-range receiver L9R.

The choice of protocol depends on the specific application and hardware configuration of the drone. For instance, some protocols may be better suited to particular remote controllers or flight controllers. Understanding the characteristics and limitations of different protocols is essential when selecting a drone system.

When selecting a flight controller for a UAV, consider the following key factors:

• Processor and Performance: The flight controller’s processor should be capable enough to handle the required tasks. Different processors like STM32 F4, F7, and H7 offer varying levels of performance and memory.
• Sensor Integration: Ensure that the flight controller supports the necessary sensors for your UAV, such as gyroscopes, accelerometer, magnetometers, barometers, and possibly GPS.
• Connectivity: Consider the connectivity options available on the flight controller, such as UARTs for GPS and telemetry, I2C for sensors, and SPI for SD cards or compasses.
• Size and Mounting Options: The physical size and mounting patterns of the flight controller should fit your UAV’s frame and design.
• Power Requirements: Check that the flight controller can handle the power requirements of your UAV, including the voltage and current for the ESCs, motors, and other peripherals.
• Firmware Support: The flight controller should be compatible with the firmware you plan to use, such as Betaflight, PX4, or ArduPilot. Consider the features and customization options offered by the firmware.
• Redundancy features: For critical applications, you may want a flight controller with redundancy features to ensure safe operation in case of a failure.
• Expandability: Consider whether you might want to add additional features or peripherals in the future and whether the flight controller can accommodate these.
• Weight: Especially for smaller UAVs, the weight of the flight controller can be a significant factor affecting performance and flight times.
• Cost: Flight controllers vary widely in price, so consider your budget and whether the additional features of a more expensive controller are worth the cost for your application.
• Safety Features: Some flight controllers come with built-in safety features such as kill switches, emergency stop functions, and return-to-home capabilities.
• Certification and Compliance: If you’re operating in a regulated environment, ensure that the flight controller meets the necessary certification and compliance standards.

When selecting a receiver for a UAV, consider the following key factors:

• Compatibility: Ensure the receiver is compatible with the UAV’s flight controller and the radio transmitter being used. This includes the right frequency band and protocol support.
• Range: The receiver should have a range that suits the operational requirements of the UAV. Consider the environment in which the UAV will operate, as this can affect signal strength and range.
• Size and Weight: The receiver should be appropriately sized and lightweight to fit the UAV’s frame without adding excessive weight.
• Power Requirements: Check that the receiver can operate with the power supply available on the UAV.
• Fail-Safe Features: It’s important to have a fail-safe feature that returns the UAV to a safe state in case of signal loss or communication failure.
• Antenna Type: Consider whether the UAV requires an external antenna for better range or if a built-in antenna is sufficient.
• Telemetry: Some receivers support telemetry, which can provide valuable data about the UAV’s status during flight.
• Binding Process: The receiver should have a binding process that is compatible with the transmitter and is easy to set up.
• Cost: Consider the cost of the receiver and whether the additional features of more expensive models are necessary for your specific application.

Control surfaces – When designing the control surfaces for an Unmanned Aerial Vehicle (UAV), several factors must be considered, including but not limited to stability, maneuverability, aerodynamic efficiency, and structural integrity. Here are some key steps and considerations:

• Development of a Flight Dynamics Model (FDM): During the conceptual and preliminary design phases, it is essential to assess the aircraft’s stability and controllability characteristics. This enables further analysis of the loads endured and maneuverability aspects.
• Selection and Sizing of Control Surfaces: The choice (such as ailerons and rudders) and sizing of control surfaces are critical for the aircraft’s stability and control capabilities. A sizing methodology for control surfaces can be employed to evaluate whether the designed control surfaces meet the critical requirements and can adequately respond to input commands.
• Calculation of Stability Parameters: This includes calculating coefficients such as the lift coefficient (CL), drag coefficient (CD), pitch moment coefficient (Cm)), roll moment coefficient (Cl), and yaw moment coefficient (Cn).
• Control Surface Efficiency: The design of the control surfaces should ensure sufficient control force and moment at various flight conditions. This involves optimizing the deflection angles, area, and position of the control surfaces relative to the aircraft’s center of gravity.
• Aerodynamic Performance Analysis: Tools such as Computational Fluid Dynamics (CFD) and wind tunnel testing are used to assess the aerodynamic performance of the control surfaces at different deflection angles.
• Structural Integrity: The design of the control surfaces must also consider structural strength and weight.

see in part Incorporate with Other Aircraft

Various methods could be applied to the UAV for its signal enhancement. This can provide them with a longer flying distance and a stabler connection in treacherous environments.

• On the UAV
  • 4G unit: In the application of drones, a 4G module can provide enhanced image transmission capabilities. If the original image transmission signal is obstructed or interfered with, users can still control the drone using the 4G network, reducing the likelihood of disconnection. Moreover, the 4G module can also achieve network RTK (Real-Time Kinematic positioning) to obtain more accurate positioning information, which is of great practical value for applications requiring high-precision positioning. For example, in applications such as remote monitoring and data transmission, drones can rely on 4G networks to achieve stable data transmission and real-time image return, providing users with more convenient and efficient services. At the same time, by accessing the 4G network and implementing enhanced image transmission and network RTK functions, the 4G module for drones can significantly improve the flight stability and safety of drones.
• On the ground
  • Change in transmit frequency: In the remote controller’s video transmission settings, select the dual-frequency mode (such as 2.4GHz and 5.8GHz) to allow the drone to automatically switch to the more suitable frequency band. The 2.4GHz band has a long transmission range but is less resistant to interference, making it suitable for open rural areas; the 5.8GHz band has strong resistance to interference but a shorter transmission range, making it suitable for urban areas with tall buildings.
  • High gain antenna: high gain antenna can significantly enhance the reception and transmission capabilities of the signal.
  • Relay Module: Relay modules are used to transfer remote control and graphic signals. It helps to enhance the signal as it passes though the gadget to reach where normal signal trasmissions cannot reach.