Interpretation of UAV Flight Control Stability PTZ Video Transmission Module Selection
Drone, digital, image
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I. Flight Control
UAV flight control system refers to a control system that can stabilize the drone's flight attitude, and can control the autonomous or semi-autonomous flight of the drone. It is the brain of the drone, and it is also the main symbol of zui that is different from the aeromodel, referred to as flight control .
The function of the flight control is to quickly adjust the four-axis flight status through the gyroscope on the flight control board (both instantaneous things, don't try to complete it with human flesh). If it is found that the power on the right is large and tilts to the left, then the current output on the right is weakened, the motor slows down and the lift is reduced, naturally it no longer tilts to the left. If there is no flight control system, the quadcopter will have an unbalanced flight power due to installation, external interference, and inconsistencies between parts. The consequence is that the left and right, up and down, and other planes will roll randomly and cannot fly at all.
The working process is roughly as follows: the flight control system collects the flight state data measured by each sensor in real time, receives the control commands and data sent from the uplink measurement and control station uplink channel transmitted by the radio measurement and control terminal, and calculates and outputs the control instructions to the executing agency to realize Control of various flight modes in UAVs and management and control of mission equipment; meanwhile, real-time transmission of UAV status data and working state parameters of engines, onboard power systems, and mission equipment to airborne radio data The terminal sends it back to the ground measurement and control station via the radio downlink channel. The hardware of the flight control system mainly includes: a main control module, a signal conditioning and interface module, a data acquisition module, and a servo drive module.
Second, stabilize the gimbal
Stabilizing the platform is too important for the task equipment. It is used to stabilize the camera. Errors in the altitude of several kilometers can be out of the range of tens of meters. It mainly senses the movement of the fuselage through sensors, and keeps the camera in its original position through motor drive to offset the effects of camera shake or vibration. The gimbal mainly examines several performances: stability enhancement accuracy, compatibility (a gimbal can adapt to several cameras and lenses), and rotation range (three axes of pitch, roll and rotation). If you encounter a zoom camera , Even more to test the stability of the gimbal accuracy, because after a long distance zoom, a little vibration will make the screen shake very much.
The current aerial gimbal is mainly driven by a brushless motor, which stabilizes the camera in three axes: horizontal, roll, and pitch. The available photographic equipment ranges from small cameras to GoPro, to micro single / mirrorless cameras, and even full Format SLRs and professional-grade movie machines are available. The larger the photographic equipment, the larger the gimbal, and the larger the corresponding frame.
The above three demonstrations are the effects of the camera body moving and the camera moving, but when the gimbal is working, the camera does not move and the camera moves. Therefore, when in the air, the body of the drone is constantly moving, and the gimbal can still maintain the position of the camera lens to achieve the effect of increasing stability.
At present, three-axis stabilization gimbals and two-axis stabilization gimbals are common on the market.
The three-axis stable aerial gimbal is the aerial anti-shake gimbal used by mainstream aerial drones, such as: EHang Ghost Drone 2.0, Zero-degree XPLORER, DJI Phantom 3 all use 3-axis aerial stabilizer, the advantage is Some pictures during aerial photography are stable to ensure clear and stable pictures. However, the disadvantage is that the engineering cost is relatively expensive. Because of the motor control, it will consume power and reduce the battery life of aerial photography.
The two-axis stable aerial gimbal is actually a reduced version of the three-axis stable aerial gimbal. It is widely used by some drones positioned on the market for low-end products. The reason is that the two-axis stabilizer can reduce costs and eliminate vertical The stability compensation on the power consumption will also help. Most of the drones used for aerial photography are axisymmetric structures, and the axisymmetric structure does not shake too much in the vertical direction. In the DJI Phantom 2 generation, the UAV's tripod is used as an antenna. In flight, it is not possible to retract the tripod, and the horizontal rotation of the aerial camera will make the aerial trip to the drone's tripod, so the actual role is not necessary, this type of aerial head.
The power consumption of drone aerial gimbal is a major factor affecting the drone flight. Some users have actually tested the power consumption of the motor that stabilizes the gimbal. If other factors are the same, the aerial gimbal is not installed. Now, the flight time can be as long as 26 minutes. After the aerial gimbal is installed, the flight time is reduced to 18 minutes, and the battery life is reduced by 30% after the aerial gimbal is installed.
The drone image transmission system is to transmit the pictures taken by the drone in the sky in a real-time and stable manner to the ground wireless image transmission remote control receiving device.
The entire image transmission work process is roughly as follows (take digital image transmission as an example): the video shooting device mounted on the drone transmits the collected video signal to the image transmission signal transmitter installed on the drone, and then the image transmission signal is sent 2.4GHz wireless signal (the drone image transmission kit sold on the market has 1.2GHz, 2.4GHz, 5.8GHz bands optional, anti-interference ability and bandwidth are different) transmitted to the ground receiving system, and the receiving system Then it is transmitted to the display device (display or flat-screen TV) via HDMI, or it is transmitted to mobile phones and tablets via USB. As a result, the operator can monitor the aerial image of the drone in real time.
UAV flight range is limited, remote control signals deteriorated at the same time, and real-time high-definition image transmission is also a problem. The distance of image transmission, the quality of image transmission, and the stability of image transmission are the key factors to measure the performance of UAV image transmission. At the same time, the performance of the image transmission system is a key factor to distinguish the grade of the UAV.
The existing image transmission mainly includes analog and digital, and its constituent parts are mainly composed of a transmitting end, a receiving end and a display end.
(1) Analog video transmission Early video transmission equipment used the analog format, which is characterized by the fact that as long as the video transmission transmitter and receiver work in a frequency band, you can receive the picture.
1) The price is low, and the simulation transmission and receiving packages on the market are usually less than 1,000 yuan;
2) Multiple video signals can be received at the same time. The transmitting end of analog image transmission is equivalent to broadcasting. As long as the frequency of the receiving end is the same as the transmitting end, the video signal can be received, which is convenient for multiple people to watch; choose more and match different antenna Can achieve different receiving effects;
3) The working distance is relatively long. Take the commonly used 600mw image transmission as an example, the working distance in open areas is above 2km;
4) With the display of snowflakes when there is no signal, it can barely judge the attitude of the aircraft when the signal is weak;
5) The technology of integrated video acceptance and DVR (video recording) and FPV dedicated video glasses is mature, and there are many product choices;
6) There is almost no delay in the video signal, which is necessary for low-altitude high-speed flight.
1) The quality of the products for transmission, reception and antenna varies, making it difficult for novice players to choose;
2) It is susceptible to co-channel interference. If the frequencies of the two transmitting ends are close, it is very likely that the video signal of this machine will be inserted by someone else's image transmission signal, causing the aircraft to be lost;
3) Wiring, installation, and debugging require certain experience, which increases learning costs for novices;
4) The process of installing and connecting antennas, receiving batteries, and display brackets during flight is cumbersome;
5) The receiving end without DVR (video recording) function cannot view the video in real time, and the receiving end with DVR function is inconvenient to view the video;
6) The analog video transmission transmitting end is usually installed outside the fuselage, which affects the aesthetics of the integrated machine;
7) If the video transmission antenna installed by the player is improperly installed, it may be blocked by the fuselage in some flight attitudes, resulting in poor reception of signals at this time and affecting flight safety;
8) The video bandwidth is small and the picture quality is poor, usually the resolution is 640 * 480, which affects the look and feel when shooting.
Adapt to the crowd: Advanced players who have a certain foundation and are enthusiastic about cross-flying and other projects (2) Digital image transmission The drone kits developed by manufacturers are usually equipped with dedicated digital image transmission. Its video transmission method is through 2.4g or 5.8g digital signal.
1) Easy to use, usually only need to install a mobile phone / tablet as a display on the remote control;
2) The image transmission quality of Chinese products is high, and the resolution can reach 720p or even 1080p;
3) The transmission distance of Chinese products can also reach 2km, which is comparable to ordinary analog image transmission;
4) It is convenient to review the photos and videos taken in real time;
5) Integrated in the fuselage, the reliability is high, and the integrated design is more beautiful.
1) The price of Chinese products is expensive;
2) The short range of low-end products and the problem of image delay are very serious, affecting the flight experience and long-distance flight safety;
3) When ordinary mobile phones and tablet computers are not equipped with a hood, when flying in an outdoor environment, the lower screen brightness makes it difficult for the pilot to see the screen clearly;
4) Due to the strength of manufacturers and R & D costs, the compatibility of different digital image transmissions for mobile phones / tablets as displays has not been fully verified, and some models may have poor adaptation.
Adapt to the crowd: novice players, Chinese digital image transmission can also adapt to player requirements, but the current digital image transmission delay for cross-flight is still longer than the external display or mobile phone / tablet as a display to achieve aerial photography.
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