FPV drone knowledge

What is a FPV drone?

FPV drones are also known as FPV drones. Unlike aerial cameras, aerial cameras pursue stability, safety and shooting capabilities for shooting. However, FPV drones pursue the fastest flight speed, fastest reaction speed and coolest operation on the track. They have the characteristics of high flight speed and short battery life.

First experience the perspective of FPV drones:

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[Master] Official FPV drone promotional video of the Turkish Tourism Bureau. This time, there are not only hot air balloons! (by: JohnnyFPV)

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Popular FPV drones

Differences between FPV drones and aerial cameras:

Different appearances:

Common aerial cameras, such as Mavic2, are shown in the figure below:

Common 250mm wheelbase FPV drones are shown in the figure below:

FPV drones used for racing need to be lighter and more agile, so they will be smaller and lighter than general aerial drones. The wheelbase of most aerial photography drones is more than 300mm; but the wheelbase of a racing drone is generally 250mm or less, and its volume is only about half of that of a general aerial photography drone, making it easier to cross various obstacles.

Internal differences:

The performance of aerial photography drones is also very different from that of racing racing drones. In order to shoot stable pictures and ensure flight safety, aerial photography drones have added a bunch of electronic equipment such as GPS, barometer, IMU, and visual sensors, and the performance of the chip is super strong. Aerial photography drones also carry a three-axis gimbal to ensure the stability of the picture and control the pitch of the picture.

The components of racing drones pursue simplicity and reduce the weight as much as possible. In many cases, there is not even a decent shell, and the bottom plate and wiring are all exposed.

Different operations:

Aerial photography drones are easy to operate, with two joysticks. No matter how you hit the sticks, the aircraft can fly very stably. When encountering obstacles, the obstacle avoidance system on the aerial photography drone can also help the drone avoid collisions with obstacles. If you don’t want to control it, just let go of your hands and the drone will hover stably.

But there are generally two modes for a drone: angle mode and manual mode. In angle mode, the pitch and roll sticks correspond to the angle of the drone, and in manual mode, the pitch and roll sticks correspond to the angular velocity of the drone. And neither has the function of setting the height, and the throttle stick of the remote controller will not return to the center. If you loosen the stick, the drone will crash. Generally, it takes a long time of training to find the feeling of control. If you have never dropped or crashed a drone, or if you have broken a few drones, you will not be able to get out of the novice village. Even the best players will inevitably crash the drone by mistake.

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The video you shoot feels different:

Composition of a drone:

A set of drones can be simply divided into the sky end and the ground end.

The sky end refers to the drone. The ground end refers to the remote controller and FPV glasses, etc.

The following introduces each component:

Frame:

The function of the frame is to carry all the components required for the drone, and also protect the core components. The most common power layout of the frame is now X-type.

Assume that the distance between the two motors at the nose is a, the distance between the two motors at the tail is c, and the distance between the two motors on the side of the frame is b.

a=c>b, called a wide X frame.

a=c<b, called a long X frame.

a=c=b, called a positive X frame.

c>a, b>a, called a special-shaped X frame.

The characteristics of the wide X frame are: very stable in the roll direction, but not flexible enough, and relatively slow in flying. Because the wide X has a long force arm in the roll direction, the motor generates the same force, and the corresponding torque is large, which is easier to adjust against some disturbances and flight control. However, because the force arm is long, the distance the motor travels is long in order to achieve the same roll attitude, so the flexibility is relatively insufficient. And because the force arm in the pitch direction is short, the acceleration of forward flight is relatively slow. Wide X and positive X are suitable for novices.

The characteristics of the long X frame are: very stable in the pitch direction and flexible in the roll direction. The reason is opposite to that of the wide X.

Features of the special-shaped X-frame: suitable for turning, because it is narrow in front and wide in the back, the control force is better when rolling and pitching at the same time. This working condition is turning, which can make the force arm of the motor on the outside of the rear arm relatively longer when turning. For example, the motor on the right rear when turning left.

There are several characteristics of the current racing frame:

1. The area where the center plate is arranged is reduced to reduce the windward area and reduce wind resistance.

2. The arm is very thin, which can also reduce the windward area. The arm is very thin, and the area of ​​the airflow under the propeller is reduced, so the propeller can generate greater pulling force.

Common frame manufacturers include: Genesis Technology, Gepu, etc.

Flight control:

Flight control is the abbreviation of flight controller, which is equivalent to the brain of the cross-country aircraft. There are generally accelerometers and gyroscopes on the flight control board, and external sensors such as GPS can also be connected. The flight control will process the data of each sensor according to the instructions of the remote control, and send instructions to the electric speed controller to control the motor speed of each axis to control the attitude of the aircraft. The flight control board usually has an interface for the remote control receiver, a USB interface for adjusting parameters by connecting to a PC, and an interface for connecting the ESC and other external devices. The layout of these interfaces on different flight control boards is different. Please refer to the manual when using them.

The flight control of the flying drone has developed from CC3D, NAZE32 to the current F4 and F7. Simply put, the chip of the flight control is constantly upgraded, the processing speed is getting faster and faster, the functional interface is getting richer and richer, and the functions are becoming more and more integrated.

Common flight control: APM; PIXHAWK; CC3D; Naze32; F3/F4; KISS/LUX

Commonly used parameter adjustment software: Cleanflight, Betaflight

Power system:

ESC:

The full name of the ESC is electronic speed regulator, which receives the control signal of the flight control and drives the motor according to the control signal. Common product forms include split ESC and 4-in-1 ESC. One thing to note is that if the split ESC has a broken one, you can replace the broken one separately, but the 4-in-1 ESC needs to replace the entire ESC. Relatively speaking, the maintenance cost will increase, but the cable management is simple and neat, and the weight reduction is also a balance that players need to balance.

The main parameters of the ESC:

1. The input voltage range supported is generally given by the number of lithium battery strings, such as 3s~6s.

2. Maximum continuous current.

3. Peak current.

4. The type of control signal supported, such as DShot1200, Multishot, PWM, etc.

5. The software function of the ESC. At present, most manufacturers' ESCs use BLHeli32 firmware.

Common ESC manufacturers include: Haoying, Dali DALRC, Tmotor, Feiying Jiale, etc.

Motor:

Generally, it is a three-phase sensorless permanent magnet synchronous motor, also called a brushless DC motor, which belongs to an AC motor. The output of the lithium battery is DC, so an ESC is needed to convert the DC into three-phase AC to control the operation of the brushless DC motor. The motor can be simply divided into two parts, the rotor and the stator. The magnet is attached to the rotor, and the enameled wire is wound on the stator. The motor used in the cross-country drone is generally an outer rotor motor.

Main parameters of the motor:

1. Motor size, generally represented by a string of numbers, such as the common 2205. The first two digits 22 represent that the outer diameter of the stator in the motor is 22mm, and the last two digits 05 represent that the stator height is 5mm.

2. KV value refers to the increase in speed for every 1V increase in voltage when the motor is unloaded. Generally, a 4S battery will be paired with a motor of about 2400KV, and a 6S battery will be paired with a motor of about 1600KV.

Common motor manufacturers include: Tmotor, Yinyan, Zhiying, dys, etc.

Propeller:

Propellers generate lift by rotating. The intuitive parameters of propellers are mainly the number of blades and the model of propellers. The model of propellers is generally represented by a string of numbers, such as 5040. The first two digits represent the diameter of the blades in inches, 50 represents 5.0 inches, and the last two digits represent the pitch in inches.

The mainstream propeller form of a cross-country drone is a 5-inch 3-blade propeller, which is relatively balanced in terms of pulling force and efficiency.

The performance of a propeller cannot be simply characterized by the 4-digit number representing the model, because the propeller type design is complex, and the working conditions of static conditions, dynamic straight lines, and dynamic turns are all different. The same 4-digit number has different performances for different propeller types.

Generally speaking, the larger the pitch, the greater the pulling force, the greater the power consumption, and the smaller the ratio of pulling force to power consumption. Therefore, for propellers with small pitch, the smaller the pulling force increment corresponding to the throttle increment, the more precise the control, the more delicate the feel, and the higher the efficiency.

The mainstream material of propellers is now PC, which has the characteristics of both explosion resistance and toughness.

Common propeller manufacturers include: Tmotor, Qianfeng, DALPROP, etc.

Power matching:

According to the size of the frame, you can determine the maximum size of the propeller you can use. Indoor units generally have 2-3 inch propellers, and there are three-blade or four-blade ones. Competition aircraft mainly have 4-5 inch propellers, and it is best to have 5 inches, which will have better power effects. Then there are ordinary cross-country aircraft, which support propellers from 4-6 inches.

After selecting the purpose, you can start to choose the motor. Generally, professional brands will provide you with test reports, including tension, voltage, current, speed and power efficiency under different propellers and different throttle amounts.

Here we need to mention a very important parameter, thrust-to-weight ratio, which is the ratio of motor thrust to weight. Here we refer to the maximum throttle thrust-to-weight ratio.

Take Tmotor's F40pro3 KV2400 motor as an example. When using GF5149 propellers, the maximum thrust is 1630g under 4s battery power supply, and the thrust of four motors is 6520g. It is estimated that our cross-country drone is about 600g, so the thrust-to-weight ratio is 10.8. And according to the test report of the motor and propeller, it can be obtained that the current of the motor reaches full throttle. The maximum continuous output current of the selected ESC should be larger than the maximum motor current, and some margin should be left. Novices control the power thrust-to-weight ratio at 4-6, which can be higher for racing or freestyle, with a thrust-to-weight ratio of more than 8, or even higher.

Battery:

There are two types of lithium batteries, one is lithium polymer battery Li-Po, and the other is lithium ion battery Li-Ion. The cross-country drone uses Li-Po lithium polymer battery.

1. Li-Po lithium polymer battery has several battery voltage nodes:

2.75V is the discharge cut-off voltage, which is the lowest point of the voltage when the manufacturer calculates the capacity.

3.6V. It is best not to be lower than this value when discharging, so as not to greatly affect the life.

3.7V is the nominal voltage value.

3.8V~3.9V is the battery storage voltage.

4.2V is the voltage of a fully charged lithium polymer battery cell.

4.35V is the voltage of a fully charged high-voltage lithium polymer battery cell.

2. Lithium battery capacity

For example, if the battery is marked with 1300mAH, it means that if it is discharged at a current of 1300mA, it can last for 1 hour. If the discharge current is 2600mA, the discharge time is 0.5 hours.

3. Charge and discharge rate, C number

If the battery capacity is still 1300mAH, 1C means 1*1300mA. If the battery is marked with a maximum discharge of 50C, the maximum discharge current of this battery is 50*1.3A=65A. The charge rate is 2C, which means the maximum charging current is 2*1.3A=2.6A. It is best to be less than the maximum charging current during charging, otherwise it will affect the battery life and capacity.

4. Combination of lithium batteries

Parallel connection P, series connection S. Parallel connection will increase the capacity of the battery, and the voltage will remain unchanged. Series connection will increase the voltage of the entire battery, but the capacity will remain unchanged. 4S2P is two groups of 4 battery packs connected in series in parallel. Generally, the batteries of cross-country drones are connected in series.

Notes on battery use:

1. The battery cannot be short-circuited, and the wire must be wrapped if it is broken

2. When assembling the aircraft battery wire, it must be tied well to prevent it from being damaged by the blades.

3. The battery cannot be over-discharged. Generally, the voltage of a single battery should not be lower than 3.6V (set an alarm buzzer or grasp the flight time)

4. After the battery is used, it can be charged to 3.8V for storage after a period of time.

A few questions:

1.Q: Does a 1300mAH battery have a shorter flight time than a 2600mAH battery?

A: Not necessarily. In terms of weight, the larger the capacity, the heavier the battery, and the heavier the weight, the more power it consumes.

In terms of discharge capacity, a 1300mAH 80C battery is more likely to fly longer than a 2600mAH 20C battery, because the discharge capacity is not enough. In violent flight, the battery will cause a large voltage drop due to insufficient discharge capacity, which will cause the voltage of a single-cell battery to reach 3.6V too quickly, although the battery voltage will rise again after the aircraft lands.

2.Q: The current battery discharge rate is seriously false.

A: Different manufacturers have different test standards, and different test environments will result in different measured discharge rates. There is another situation, I want to buy a 1300mAH 70C battery, but the manufacturer gave me a 1500mAH 60C battery. Their maximum currents are about 1.3A*70 = 91A, 1.5A*60 = 90A. The cost increase brought by the high C number is higher than the increase in capacity.

Common battery manufacturers include: Format, Flower Card, etc.

DJI FPV digital image transmission system:

The DJI FPV digital image transmission system includes four main components: FPV flight goggles, image transmission module, camera and remote control. This new image transmission system is a high-definition, ultra-low latency image transmission solution specially designed by DJI for cross-flight. It adopts 720p/120fps high-definition and high-frame rate image transmission, and the end-to-end image transmission delay is as low as 28ms. At the same time, the parameters of the camera, glasses and image transmission can be adjusted remotely. The air end supports up to 8 independent communication frequency bands, and has functions such as image transmission and recording, remote control reception, and multi-antenna transmission and reception. It supports up to 8 5.8GHz communication frequency bands, enabling 8 drones to fly simultaneously. Traditional drones have always used analog signals for image transmission, and the transmission quality is poor.