Lei Feng network (search "Lei Feng network" public number attention) by: Author of this article drone channel (id: auscor), concerned about the drone industry.
The flight control system is the core control device of the drone and is equivalent to the brain of the drone. Whether the flight control system is installed or not is also an important sign that the drone is different from the ordinary aviation model.
After experiencing early remote control flights, its current navigation control methods have evolved into autonomous flight and intelligent flight . The change of navigation methods puts higher requirements on the accuracy of the flight control computer; as the complexity of the mission of the small drone is increased, the requirements for the flight speed of the flight control computer are also higher; and the requirements for miniaturization are on the flight control. The power consumption and volume of the computer also put forward high requirements . High precision not only requires the computer's high control accuracy, but also requires the ability to run complex control algorithms. Miniaturization requires the small size and mobility of the drone, which in turn requires the control computer to be as small as possible.
Among the many processor chips, the most suitable chip for small-scale flight control computer CPUs is the TMS320LF2407 from TI. Its operation speed and numerous peripheral interface circuits are suitable for real-time control of small drones.
It uses Harvard architecture and multi-stage pipeline operations to read data and instructions simultaneously. The on-chip resources include 16 10-bit A/D converters with automatic sorting function to ensure that up to 16 channels are converted during the same conversion period. Perform without increasing the overhead of the CPU; 40 universal input/output channels that can be individually programmed or multiplexed; 5 external interrupts; and an integrated serial communication interface (SCI) that enables it to be equipped with other controllers within the system Asynchronous (RS 485) communication capability; 16-bit Synchronous Serial Peripheral Interface (SPI) can be easily used to communicate with other peripheral devices; also provides watchdog timer module (WDT) and CAN communication module.
Flight Control System ComponentsThe flight control system collects the flight state data measured by each sensor in real time, and receives the control commands and data sent by the radio monitoring and control terminal from the uplink channel of the ground monitoring station. After calculation and processing, the control command is output to the implementing agency to realize the realization of the drone. The control of various flight modalities and the management and control of the mission equipment; at the same time, the status data of the drone and the working status parameters of the engine, the airborne power supply system and the mission equipment are transmitted in real time to the airborne radio data terminal, and are transmitted via the radio. The channel is sent back to the ground station.
According to the function division, the hardware of the flight control system includes: a main control module, a signal conditioning and interface module, a data acquisition module, and a servo drive module .
Module functionEach function module is grouped together to form the core of the flight control system. The main control module is the core of the flight control system. It is combined with the signal conditioning module, interface module and servo drive module. It only needs to modify the software and simply modify the peripheral circuit. On the basis of this, it can meet the flight control and flight management functional requirements of a series of small drones, so as to realize the purpose of one-time development, multi-model use, and reduction of system development costs. The system mainly completes the following functions:
(1) Complete high-precision acquisition of multi-channel analog signals, including gyro signals, heading signals, rudder angle signals, engine speed, cylinder temperature signals, dynamic and static pressure sensor signals, and power supply voltage signals.
Since the accuracy of the CPU's own A/D and the number of channels are limited, an additional data acquisition circuit is used. The chip select and control signals are generated by the decoding circuit in the EPLD.
(2) The output switch signal, analog signal and PWM pulse signal can meet the control requirements of different actuators (such as rudder, aileron servo, elevator servo, air channel and throttle servo).
(3) Using multiple communication channels to achieve communication with airborne data terminals, GPS signals, digital sensors, and related task devices, respectively. Since the serial port configured by the CPU's own SCI channel cannot meet the system requirements, a multi-serial expansion chip 28C94 is used in the design to expand 8 serial ports.
System software designThe software design of the system is divided into two parts, namely the programming of EPLD decoding circuit of the logic circuit chip and the application programming of the flight control system.
EPLD is used to constitute the digital logic control circuit, complete the decoding and isolation and provide chip select signals and read/write control signals for A/D, D/A, and 28C94.
The design of the software adopts a mixed design method of schematic input and VERILOG HDL language programming, following the design input → design implementation → design verification → device programming process. The system uses two ispLSI1048 chips, which are used to implement control of A/D and D/A and control of the serial port expansion chip 28C94. The parameters are derived from the UAV.
System Application DesignBecause C language can not only write application programs and system programs, but also can directly control computer hardware like assembly language, and the written programs are highly portable. Since the DSP-based system involves a large number of operations on the peripheral ports, and considering the follow-up program transplant work, the flight control system applications are designed using BC 3.1 to achieve flight control and flight management functions, respectively.
The software is divided into 4 modules according to the function: time management module, data acquisition and processing module, communication module, control law solving module.
Through the time management module , the UAV is controlled in real time in the millisecond time; the data acquisition module collects the drone's flight status, attitude parameters, flight parameters, flight status and flight parameters for telemetry coding and transmits it to the machine through the serial interface. The data-carrying terminal is sent to the ground control station via the wireless data channel for flight monitoring; the attitude parameters are sent to the control law solving module through the software's internal interface for solving, and the result is sent to the on-board servo system through the D/A channel to control the steering gear. Operation, to achieve the purpose of adjustment, aircraft flight attitude; communication module to complete the data exchange between the flight control computer and other airborne peripherals.
The use of high-speed DSP control chip in the control law calculation and data processing advantages and rich external resources, with a large-scale programmable logic device CPLD and serial interface expansion chip 28C94 design small airborne flight control computer, with its core design The small drone flight control system has the characteristics of full-featured, small size, light weight, and low power consumption, and it satisfies the requirements of high-precision, miniaturization, and low-cost of the flight control computer for small-sized drones. The design has been successfully applied to a verification drone system.