Despite the fact that quadcopters are an extremely fashionable topic, choosing components to assemble your device is still not so easy. Selecting parts for a specific project is a painful search for the optimal combination of weight, power and functionality. Therefore, before plunging into the world of countless online stores and nameless Chinese manufacturers, let's do the preparatory work.

What is a quadcopter and why is it needed?

Multirotors, also known as multicopters or simply copters, are unmanned aerial vehicles designed for entertainment, taking photos and videos from the air, or testing automated systems.

Copters are usually distinguished by the number of motors used - ranging from a bicopter with two motors (like GunShip from the movie Avatar) to an octacopter with eight. In fact, the number of motors is limited only by your imagination, budget and the capabilities of the flight controller. The classic version is a quadcopter with four motors located on intersecting beams. The Frenchman Étienne Oehmichen tried to build such a configuration back in 1920, and in 1922 he even succeeded. Essentially, this is the easiest and cheapest option to make an aircraft that can easily lift small cameras like a GoPro into the air. But if you are going to take off with serious photo and video equipment, then you should choose a copter with a large number of motors - this will not only increase the load capacity, but also add reliability if one or more motors fail during the flight.

Flight theory

In flight theory (aerodynamics), it is customary to distinguish three angles (or three axes of rotation), which determine the orientation and direction of the aircraft’s motion vector. Simply put, the aircraft “looks” somewhere and moves somewhere. Moreover, he may not move in the direction he is “looking.” Even airplanes in flight have some kind of “drift” component that takes them away from their course direction. And helicopters can generally fly sideways.

These three angles are commonly called roll, pitch and yaw. Roll is the rotation of the vehicle around its longitudinal axis (the axis that runs from nose to tail). Pitch is a rotation around its transverse axis (pecks its nose, lifts its tail). Yaw is a rotation around a vertical axis, most similar to rotation in the “ground” sense.

Basic maneuvers (from left to right): straight, roll/pitch, and yaw

In the classic helicopter design, the main rotor controls roll and pitch using a blade swashplate. Since the main rotor has non-zero air resistance, the helicopter experiences a torque directed in the direction opposite to the rotation of the rotor, and to compensate for it, the helicopter has a tail rotor. By changing the performance of the tail rotor (revolutions or pitch), a classic helicopter controls its yaw. In our case, everything is more complicated. We have four screws, two of them rotate clockwise, two counterclockwise. Most configurations use fixed-pitch propellers and can only be controlled by their speed. If they all rotate at the same speed, they will cancel each other out: yaw, roll and pitch will be zero.

If we increase the RPM of one clockwise rotating propeller and decrease the RPM of the other clockwise rotating propeller, then we maintain the total torque and yaw will still be zero, but roll or pitch (depending on where we do his “nose”) will change. And if we increase the speed on both propellers rotating clockwise, and reduce the speed on the propellers rotating counterclockwise (to maintain the total lift), then a torque will arise that will change the yaw angle. It’s clear that all this will not be done by us ourselves, but by an on-board computer that will receive a signal from the control sticks, add corrections from the accelerometer and gyroscope, and turn the screws as needed. In order to design a copter, it is necessary to find a balance between weight, flight time, engine power and other characteristics. All this depends on specific tasks. Everyone wants a quad to fly higher, faster and longer, but the average flight time is between 10 and 20 minutes depending on battery capacity and overall flight weight. It is worth remembering that all characteristics are interconnected and, for example, an increase in battery capacity will lead to an increase in weight and, as a result, a decrease in flight time. To find out approximately how long your structure will hang in the air and whether it will even be able to get off the ground, there is a good online calculator ecalc.ch. But before you enter data into it, you need to formulate the requirements for the future device. Will you be installing a camera or other equipment on the device? How fast should the device be? How far do you need to fly? Let's look at the characteristics of the various components.

PX4 - on-board computer with a full UNIX system

Frame

The main point to decide when choosing a frame is whether you will use a ready-made frame or make one yourself. With a ready-made frame, everything is simpler, and in any case you will have to order a lot of parts. At the same time, given the prices in Chinese stores, the homemade option may be more expensive. On the other hand, it will be easier to repair your own frame in the event of an accident. Well, of course, you can make any design, even the craziest one, with your own hands. Let's take a closer look at the self-assembly option.

You can make a frame from any available materials (wood, aluminum, plastic, and so on). You can get a little more serious and cut it on a CNC machine from woven carbon fiber, and you can complicate the task and make a folding structure.

The easiest option for DIY enthusiasts is to go to OBI, Leroy Merlin or the construction market and buy a 12 × 12 square aluminum pipe, as well as a 1.5 mm thick aluminum sheet. In order to make a frame from such “four sticks and fasteners” type materials, a drill or a hacksaw for metal is enough. But you need to be prepared for the fact that such a design will not last long. Still, all these profiles are made of very soft material (AD31/AD33), which will bend easily during flights.

Oehmichen No. 2, a manned quadcopter by French engineer Etienne Oehmichen, launched in 1922

As a sample for your frame, you can take a simplified factory frame or find a ready-made drawing on the Internet. More complex materials (for example, carbon fiber) can be replaced with aluminum - if it turns out to be heavier, it will not be by much. In any case, you should pay attention to the length and symmetry of the rays. The length of the beams is selected based on the diameter of the propellers used, so that after their installation the distance between the circles of the rotating propellers is at least 1–2 cm, and even more so these circles should not intersect. Motors mounted on the arms should be equidistant from the center of the frame, where the “brain” will be located, and (in most cases) be the same distance from each other, forming an equilateral polygon.

When designing, it is worth considering that the center of the frame must coincide with the center of gravity, so installing a battery at the rear between the beams is a bad idea unless it is compensated by a load in the front, such as a camera. Think about what your device will land on; for beginners, you can advise using something soft on the “belly” or ends of the arms, for example, dense foam rubber or tennis balls. And also protect the battery in case of an unsuccessful landing, for example by installing it between the frame plates or placing it under high landing skis.

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Flight in First Person View (FPV) is very exciting, especially if you use video goggles and HeadTracker, which will follow the movements of your head on the FPV camera gimbal, creating the feeling of being in the cockpit.

Motors and propellers

Due to the rotation of the motors in different directions, it is necessary to use multidirectional propellers: forward rotation (counterclockwise) and reverse rotation (clockwise). Typically two-bladed propellers are used, they are easier to balance and find in stores, while three-bladed ones will give more thrust with a smaller propeller diameter, but will cause a lot of headaches when balancing. A bad (cheap and unbalanced) propeller can fall apart in flight or cause strong vibrations that are transmitted to the flight controller sensors. This will lead to serious problems with stabilization and will cause a lot of blur and “jelly” in the video if you are filming something from a quadcopter or flying in first person view.

Speed ​​controller,
aka ESC

Any propeller has two main parameters: diameter and pitch. They are designated variously as 10×4.5, 10×45, or simply 1045. This means the propeller has a diameter of 10 inches and a pitch of 4.5 inches. The longer the propeller and the greater the pitch, the more thrust it can create, but at the same time the load on the motor will increase and the current consumption will increase, as a result it can overheat and the electronics will fail. Therefore, the screws are matched to the motor. Well, or a motor for propellers, depending on how you look at it. Usually on the websites of motor sellers you can find information about recommended propellers and batteries for the selected motor, as well as tests of the generated thrust and efficiency. There are also propellers with variable pitch, which in theory will increase maneuverability, but in reality will add complex mechanics that tend to wear out and break, followed by expensive repairs.

Also, the larger the propeller, the greater its inertia. If you need maneuverability, it is better to choose propellers with a large pitch or three blades. With the same size, they create 1.2–1.5 times more thrust. It is clear that the propellers and their rotation speed must be selected so that they can create a thrust greater than the weight of the apparatus.

And finally, brushless motors. Motors have a key parameter - kV. This is the number of revolutions per minute that the motor will make per volt of voltage applied. This is not the power of the engine, it is its, so to speak, “gear ratio”. The lower the kV, the lower the speed, but the higher the torque. The more kV at the same power, the higher the speed and the lower the torque. When choosing a motor, they are guided by the fact that in normal mode it will operate at 50% of the maximum power. Don't think that the higher the kV, the better; for copters with a typical 3S battery, the recommended number is in the range from 700 to 1000 kV.

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A more durable material is duralumin (D16T). It practically does not bend, is quite springy, and is used in aviation. Profiles from it are not sold at OBI, but you can catch them at the Mitinsky market on the third floor; they were also at the Stroy TVC market.

Power and power controllers

The captain suggests: the greater the engine power, the more battery it needs. A large battery is not only about its capacity (read: flight time), but also about the maximum current it delivers. But the larger the battery, the greater its weight, which forces us to adjust our estimates regarding propellers and motors. These days, everyone uses lithium polymer (LiPo) batteries. They are light, capacious, with a high discharge current. The only negative is that they do not work well at subzero temperatures, but if you keep them in your pocket and connect them immediately before the flight, then during the discharge they themselves warm up slightly and do not have time to freeze. LiPo cells produce a voltage of 3.7 V.

When choosing a battery, you should pay attention to three of its parameters: capacity, measured in milliamp-hours, maximum discharge current in the battery capacity (C) and the number of cells (S). The first two parameters are interconnected, and when you multiply them, you will find out how much current this battery can supply for a long time. For example, your motors consume 10 A each and there are four of them, and the battery has parameters of 2200 mAh 30/40C, so the copter requires 4 10 A = 40 A, and the battery can produce 2.2 A 30 = 66 A or 2.2 A 40 = 88 A for 5–10 seconds, which will clearly be enough to power the device. Also, these coefficients directly affect the weight of the battery. Attention! If there is not enough current, then at best the battery will inflate and fail, and at worst it will catch fire or explode; this can also happen if there is a short circuit, damage or improper storage and charging conditions, so use specialized chargers, store batteries in special non-flammable bags and fly with a “beeper” that will warn of discharge. The number of cells (S) indicates the number of LiPo cells in the battery, each cell produces 3.7 V, and, for example, a 3S battery will supply approximately 11.1 V. It is worth paying attention to this parameter, since the speed depends on it engine speed and type of regulators used.

Battery elements are combined in series or in parallel. When connected in series, the voltage increases, when connected in parallel, the capacitance increases. The connection diagram of the elements in the battery can be understood by its markings. For example, 3S1P (or simply 3S) is three elements connected in series. The voltage of such a battery will be 11.1 V. 4S2P is eight elements, two groups, connected in parallel with four serial elements.

However, the motors are not connected to the battery directly, but through so-called speed controllers. Speed ​​controllers (also known as ESCs) control the rotation speed of the motors, making your copter balance in place or fly in the desired direction. Most regulators have a built-in 5V current regulator, from which you can power the electronics (particularly the “brain”), or you can use a separate current regulator (UBEC). Speed ​​controllers are selected based on the current consumption of the motor, as well as the possibility of flashing. Conventional controllers are quite slow in terms of response to the incoming signal and have many unnecessary settings for copter construction, so they are flashed with custom SimonK or BLHeli firmware. The Chinese have come to the rescue here too, and you can often find speed controllers with already updated firmware. Do not forget that such regulators do not monitor the condition of the battery and can discharge it below 3.0 V per cell, which will lead to its damage. But at the same time, on conventional ESCs it is worth switching the type of battery used from LiPo to NiMH or disabling the reduction in speed when the power source is discharged (according to the instructions), so that at the end of the flight the motor does not suddenly turn off and your drone does not fall.

The motors are connected to the speed controller with three wires, the sequence does not matter, but if you swap any two of the three wires, the motor will rotate in the opposite direction, which is very important for copters.

The two power wires coming from the regulator must be connected to the battery. DON'T CONFUSE THE POLARITY! In general, for convenience, the regulators are connected not to the battery itself, but to the so-called Power Distribution Module - an energy distribution module. This, in general, is just a board on which the power wires of the regulators are soldered, the branchings for them are soldered, and the power cable going to the battery is soldered. Of course, the battery does not need to be soldered, but must be connected through a connector. You don't want to re-solder the battery every time it dies.

On-board computer and sensors

The choice of flight controllers for copters is very large - from the simple and cheap KapteinKUK and several open source projects for Arduino-compatible controllers to the expensive commercial DJI Wookong. If you are a real hacker, then closed controllers should not interest you much, while open projects, and even those based on the popular Arduino, will attract many programmers. The capabilities of any flight controller can be judged by the sensors used in it:

The gyroscope allows you to hold the copter at a certain angle and is included in all controllers; the accelerometer helps determine the position of the copter relative to the ground and aligns it parallel to the horizon (comfortable flight); The barometer makes it possible to keep the device at a certain altitude. The readings of this sensor are greatly influenced by air flows from the propellers, so you should hide it under a piece of foam rubber or sponge; The compass and GPS together add functions such as heading hold, position hold, return to starting point and route assignments (autonomous flight). You should approach the installation of the compass carefully, since its readings are greatly influenced by nearby metal objects or power wires, which is why the “brains” will not be able to determine the correct direction of movement; sonar or ultrasonic rangefinder is used for more accurate altitude retention and autonomous landing; the optical sensor from the mouse is used to maintain position at low altitudes; Current sensors determine the remaining battery charge and can activate return to launch or landing functions.

There are currently three main open source projects: MultiWii, ArduCopter and its ported version MegaPirateNG. MultiWii is the simplest of them, requiring an Arduino with a 328p, 32u4 or 1280/2560 processor and at least one gyroscope sensor to run. ArduCopter is a project packed with all sorts of functionality, from simple hovering to performing complex route tasks, but it requires special hardware based on two ATmega chips. MegaPirateNG is an ArduCopter clone that can run on a regular Arduino with a 2560 chip and a minimal set of sensors including a gyroscope, accelerometer, barometer and compass. Supports all the same features as the original, but always catches up in development.

Advanced nine-
channel remote control

The situation with hardware for open projects is similar, as with frames for copters, that is, you can buy a ready-made controller or assemble it yourself from scratch or based on Arduino. Before buying, you should always pay attention to the sensors used in the board, since technology development does not stand still, and the old ones somehow need to be sold to the Chinese, and besides, not all sensors can be supported by open firmware.

Finally, it is worth mentioning one more computer - PX4, which differs from Arduino clones in that it has a UNIX-like real-time operating system, with a shell, processes and everything. But we must warn you that PX4 is a new and rather crude platform. It will not fly immediately after assembly.

Setting up flight parameters, like the setup program, is very individual for each project, and the theory on it could take another article, so in short: almost all firmware for multicopters are based on a PID controller, and the main parameter that requires intervention is the proportional component , denoted as P or rateP. If during takeoff your copter twitches from side to side, then this value should be reduced, but if it reacts sluggishly to external influences, then on the contrary, increase it; you can find other nuances in the instructions and on the developers’ websites.

Safety

All beginners, when thinking about safety, remember the AR.Drone and its propeller protection. This is a good option, and it works, but only on small and light devices, and when the weight of your copter begins to approach two kilograms or has long exceeded this figure, then only a strong iron structure can save you, which will weigh a lot and, like you you see, it will greatly reduce the load capacity and flight autonomy. Therefore, it is better to first train away from people and property that can be damaged, and as your skills improve, protection will no longer be needed. But even if you are an experienced pilot, do not forget about safety precautions and think through the possible negative consequences of your flight in emergency situations, especially when flying in crowded places. Do not forget that a failure of the controller or communication channel can lead to the device flying far away from you, and then a GPS tracker installed in advance on the copter, or a simple but very loud beeper, by the sound of which you you can determine its location. Set up and check in advance the fail safe function of your flight controller, which will help you land or return the copter to the starting point if the signal from the remote control is lost.

Control

A little about radio equipment. Nowadays, almost all transmitters for flying models operate at a frequency of 2.4 GHz. They are quite long-range, and this frequency range is not as noisy as, for example, 900 MHz. For flight, four channels are generally sufficient: throttle, yaw, pitch, and roll. Well, eight channels are definitely enough for something else.

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To fly with a camera, get a gimbal that will keep the camera parallel to the horizon during maneuvers and also help control the camera's tilt. Most controllers have outputs for stabilizing servo-driven gimbals, as well as an output for a camera shutter button control switch.

The kit usually consists of the remote control itself and the receiver. The receiver contains control knobs and additional buttons. Typically, Mode2 equipment is selected, when the left stick controls the gas and rotation, and the right stick controls the tilt of the copter. All handles, except the gas, are spring-loaded and return to their original position when released. It is also worth paying attention to the number of channels. The drone will require four control channels and one channel for switching flight modes, and additional channels may also be required for camera control, for configuration, or for special flight controller modes. When choosing a remote control, you should also consider the possibility of changing the radio module so that it can be easily updated in the future.

Today in this article you will learn fundamental knowledge about rotary propellers for a quadcopter (which are also called props). What indicators influence their productivity and efficiency. What shape and how many blades should a propeller have so as not to reduce the thrust?

What you need to know: basic definitions and concepts

Propellers for quadcopters are divided according to the following criteria:

• what is their length;
• what is their pitch;
• what is the area of ​​the propellers;
• what is the direction of rotation;
• what shape do they have?
• and how many blades are on each propeller;

Propeller length and pitch

Length and pitch are the main parameters that determine traction. As the propeller rotates, the blades form a disk. The diameter of this disk is the length. The pitch is understood as the distance that a screw can cover in one rotation, in some dense environment (if you remember a screw and how it is screwed into a board, then everything becomes clear). The pitch size of the quadcopter blades depends on the inclination of the blades themselves and the angle at which they are located (angle of attack).

The thrust is considered strong when the propeller-motor group (VMG) moves a large volume of air with its screws. By increasing the length, pitch, or any one of these parameters, where the rotation speed remains unchanged, the thrust of the propellers increases. At the same time, turbulence is formed due to increased air resistance. And as a result, the large radius of the propeller and the angle of inclination of the blades will require large amounts of energy, due to which the flight time will be reduced.

Large propellers with a small pitch are ideal for aerial photography, while small propellers with a large pitch are suitable for racing drones where flight speed is important.

Number and shape of propeller blades

The standard option is considered to be a propeller with two blades. Most small quadcopters have propellers with more than two blades. This allows for a more uniform air distribution flow and, as a result, reduces the level of turbulence. In addition, due to the additional blades, the lifting force increases. Thus, a small diameter propeller with three (or more) blades can provide the lifting power of a standard larger diameter two blade propeller. The responsiveness of a quadcopter also depends on the number of blades on the propeller, and the more blades there are, the more responsive the drone is in flight. The cost of such multi-blade propellers is more expensive than standard ones, and there are difficulties in manufacturing and aligning these propellers. Such screws should be purchased from manufacturers or authorized dealers.

Take a closer look at the differences in the shapes of the ends of the blades. They are divided into three categories:

• Normal;
• Bullnose (BN);
• Hybrid Bullnose (HBN);

Normal propellers allow you to save battery consumption due to less thrust, and have a beneficial effect on flight duration without causing additional waste of energy. Normal screws have pointed tips. The equal diameter of the BN screws with their large area creates greater thrust. This advantage is accompanied by a disadvantage - a decrease in flight time due to high energy consumption. The available weights on the tips of the props help increase torque and increase the response speed of the quadcopter along the yaw axis. As for HBN nibs, they fall between Normal and Bullnose.

Direction of rotation

Motors, which are divided into two types, are responsible for the direction of rotation of the blades:

• CW – rotates the propeller clockwise;
• CCW – rotates the propeller counterclockwise;

The installation principle of such motors depends on the design of the quadcopter. The diagrams are shown more clearly in the figure.

By the edge of the blade you can determine in which direction it rotates.

Plastic and carbon: where is quality and efficiency?

Plastic propellers are more popular. Their distinctive features are:

• plastic;
• low price;
• large selection of assortment;
• availability;

It is also worth noting that more flexible blades have increased resistance to deformation when hitting an obstacle, but at the same time, there are errors in balancing.

Carbon blades are also available on the market. Carbon screws are expensive, but have a number of positive criteria:

• strength;
• efficiency;
• ease;

There are also hybrid propellers made of plastic and carbon fiber on the market. The second usually enhances the first. Propellers of this type are cheap in price and are not inferior in quality and rigidity to pure carbon ones.

The quality of props refers to how well they are made. Proper manufacturing of propellers ensures good balance during flight and does not create additional vibration of the VMG. The brands that produce the best propellers for quadcopters and other aircraft are GWS. They also recommend APC, which is produced by Americans, and EMP, which has a large assortment of products, not just accessories.

Specification and characteristics

To understand the parameters of a particular propeller, you should look at the encoding. Manufacturers indicate the length, pitch and number of blades in this format:

LLPPxB or LxPxB – where L is the length of the blade, P is the pitch (indicated in inches) and B is the number of blades.

Using an example, we will analyze two different notation formats:

So the first prop, marked 6045 (6 by 4.5), indicates that the propeller has two blades (according to the standard), 6 inches long and 4.5 inches pitch.
The second already indicates the number of blades 5040 by 3 (5 by 4 and 3), where 3 at the end is exactly the number of blades. And 5 and 4 inches, length and pitch respectively.

In some cases, designations for the direction of rotation are indicated. They are indicated in Latin letters - R and C. Thus, propellers marked (C) are placed on CCW engines, and those marked (R) are placed on engines with CW. Some other manufacturers indicate the abbreviations of what they are made of: BN, which means with pointed tips and weights, or HBN - a hybrid of plastic and carbon (we talked about them above).

Installation Methods

There are different ways to install propellers on a quadcopter. Often the shaft of an electric motor is nothing more than a metal pin. Without any auxiliary elements for installing the screw. For such cases, collet clamps and propsavers are used - these are special adapters.

When creating your own quadcopter models, it is convenient to use propsavers (see photo). A propsaver is similar to a bushing. In the side part of the surface there is one hole on each side, made symmetrically. This design is installed on the shaft and tightened with screws. Next, the propeller needs to be put on the shaft and secured with nylon ties; there is also the option of fastening with rubber rings.

The collet clamp is more reliable than the propsaver. Its design is built by a cone-shaped bushing with a threaded connection. First, a collet is installed on the shaft, then a clamping sleeve with a propeller and a washer comes. The entire adapter is secured with a specially shaped spinner nut.

On Outrunner class motors, where the brushless motor rotor is located on the outside, there are several holes in the upper part of the structure for installing various types of adapters and fasteners.

DJI, when producing its quadcopters with brushless motors, install self-tightening nuts. Threads on the shafts of this type of engine whose rotors rotate in the opposite direction.

Balancing propellers using available tools

Purchased cheap propellers may not be 100% balanced unless they are wholesale branded propellers. Such propellers negatively affect the operation of the VMG, which causes additional vibrations and, as a result, a “jelly effect” appears when shooting video. In addition to the quality of video recording, the engines also suffer. Constant vibrations have a negative impact on motors, bearings and gears, thereby increasing the cost of maintaining the quadcopter.

In this case, a procedure for balancing the details for the quadcopter will be required. To complete it you will need:

• screw;
• scotch;
• superglue (if you don’t have tape);
• sandpaper;
• balancer for propellers (in this example, Du-Bro Tru-Spin is considered, or you can use Chinese analogues, as in the video);

To begin balancing, place the device on a level surface so that the axis is aligned horizontally.

Before balancing, the blades must be checked for damage, then installed on the axis and slightly tilted in the desired direction. Next, we look at the horizontal position of the propeller, whether it managed to return after deflection. If not, then you need to lighten the heavier blade (with sandpaper). You can stick tape on a lighter blade or apply nail polish to it if you have some on hand. If there is neither one nor the other, use superglue.

When turning the balancing machine, you need to make sure that the propeller maintains balance in this position. We emphasize that all procedures for making the blades heavier and lighter must be carried out from the inside (concave).

Next, we carry out the procedure for balancing the hub. We move the propeller vertically, and see if there are deviations in one direction, then you need to weight the opposite one. You can make it heavier using varnish or superglue. We achieve balance, change the position - turn it over, and make sure that balance is achieved on the other side. This completes the balancing of the propeller blades.

eCalc calculator

To calculate propeller parameters when creating your own models of unmanned aerial vehicles, there is a very convenient service - eCalc. Many who assemble quadcopters with their own hands know about this online calculator. The section that provides calculation parameters for quadcopters is as follows.

At first it may seem that everything is clear. But you should be aware of some points that greatly influence the results of the calculations performed.

Initially, you need to specify the takeoff weight of the copter. If there are gimbals and cameras, then they also need to be included in this parameter. If the service shows Without Drive (which means “without a drive”), then you need to indicate the total weight of the frame, and the weight of other components, such as:

• propellers;
• boards;
• controller;
• suspension;
• camera;
• equipment for FPV flights.

It is also necessary to add +10% to the mass, which the wires will occupy. The output is the desired figure for the total take-off weight of the quadcopter.

We indicate the total number of rotors, according to what pattern they are located - single or coaxial. We indicate the upper limit - flight altitude, weather conditions during the flight - air temperature and atmospheric pressure).

The drop-down list prompts you to select a battery. If you do not have the required battery, choose the one that is closest in terms of current output and capacity. Next, the system will complete filling out the fields itself. We indicate the weight and structure of the battery. If you need to install additional batteries, indicate their number in the P text field. And in the Weight field their total weight is indicated.

In this field, in the drop-down list we indicate the ESC type, the so-called max. current of these regulators.

We indicate the motor manufacturer. His rating appears in the window. The KV indicators indicate the required sample.

Now we indicate the parameters of the propellers - type, diameter and pitch. If possible, use a screw with the largest diameter allowed for the frame. Specify the gear ratio if the drive has a gear transmission. Number of teeth on the guide gear to the driven gear.

If the system does not provide the necessary parameters, then you can specify it in the Custom text field. And there indicate the necessary parameters for calculation in the calculator. Keep in mind that battery parameters are indicated in one cell.

After filling in all fields, calculations are performed. At the output you will receive the necessary data. They are depicted in the form of graphs, lists and dials.

RashVinta is a program that calculates propeller parameters not only for quadcopters, but also for other aircraft.

With RashVinta you can do calculations with source data, such as:
Engine power and propeller diameter;
Engine power and propeller speed;
Screw diameter and pitch.

In the first case, check the box only on the “calculation by screw diameter” parameter. We indicate information about the size of the propeller, engine power, flight speed - maximum and average. Click “Calculate” and see the pitch parameters and propeller rotation frequency.

In the second case, all marks are removed. Next, as in the first case, we indicate the initial engine power, and also do not forget about the rotor speed and the speed of the aircraft, similar to the first case. Click “Calculate” and see all the necessary data on the diameter of the screw and its pitch.

In the third case, calculations are made at a professional level. Check the box “specify screw parameters”. We enter the parameters of the diameter and pitch of the screw in the required fields. Click “Calculate” and see the data on the profile of the propeller blade, its image appears in the window. You can change the scale to study it. All calculation conclusions are saved in the form of tables in the date.html format provided in the program assembly.

The program allows you to see the profile of the blade at an angle of inclination. To do this, check the “Profile with angle” checkbox. And you can also see the points that were used for the calculation - check the box “show calculated points”. On a printer, this profile image can be printed on paper in a 1:1 projection.

Conclusion about the complexity of the procedure

As you have already noticed, the work of selecting and adjusting details is quite a difficult task for a beginner. But I hope that this article will be useful for fans of quadcopters and other unmanned aircraft, to correctly carry out the procedure for balancing propellers and installing them on a quadcopter with a homemade design. And also get rid of errors in the operation of the VMG of serial models of multicopters.

Useful tips for choosing a propeller group.

You can’t even imagine (if you haven’t attended an aircraft modeling club) how many mathematical and aerodynamic calculations need to be carried out to designers when designing a propeller-engine group of an aircraft.

At the same time, you are already familiar in practice with the difficulty of choosing the right combination "motor - main rotor" for getting best flight characteristics.

To my happiness and yours, this knowledge does not belong to state secrets at all (at least during the construction of SMALL quadcopters), and many enthusiasts blow their cheeks and spread their experience via the Internet and printed publications.

As a section of the manual on creating your own quadcopter (, and, and even here and here, the author decided to share information with beginners on how to choose goods in the store elements of the propeller group for quadcopter. However, according to him, this skill will also be useful to creators of similar types aircraft with a different number of rotors.

Engine selection

When choosing an engine, it's always a good idea to research it first. characteristics, which written on the label provided by the seller and manufacturer. The author recommends that before purchasing, be sure to study all the characteristics of the product you like. As an example, he provides a link to the site Hobbyking.com, or rather, to the one offered for sale on it brushless motor for models.

Let's look at the given characteristics:

Weight – 10 grams

Maximum current consumption – 5.5 Amperes

Resistance – 0 mH

Maximum voltage – 7 Volts

Power (in Watts) – 210 Watts (This is not an error! Indicated on the seller’s website!)

Shaft diameter – 2 mm

Length – 22 mm

Diameter – 18

Total length – 30 mm

Product Specification:

Weight: 10 grams (including mounting and wires)

No load consumption: 0.4 Ampere

Thrust: 130 grams at 5000 rpm

Rotation speed without load: 15000 rpm. at 7.4 Volts

Peak consumption: 5.5 Amps

Shaft diameter: 2mm

Motor diameter: 18mm

Length: 30 mm (including shaft length and mounting dimensions)

When choosing an engine, you must first decide on flight weight your quadcopter, as well as traction necessary for him to get off the ground.

The main condition is that the thrust must be twice as large as the maximum flight weight of the structure.

Insufficient traction engines will lead to poor handling or monument to quadcopter the aircraft's inability to take off. At the same time, too much traction will lead to excessive sharp reaction of the quadcopter on control devices and flight instability.

The required thrust can be estimated using the following formula: Required thrust = (Total mass of the structure* 2)/4.

Let's give an example. If your quadcopter has flight weight(or takeoff - when using an internal combustion engine or building a bomber) is about 1 kilogram, then calculating using the above ratio, we get necessary traction at 2 kilograms. This means that each engine must have about 500 grams of thrust. Of course, the calculation must take into account the full structure weight, in particular, the masses of engines and propellers. If you dream of aerial photography or video shooting, do not forget to add the weight of the camera and its power sources.

Although the choice of flight weight is up to you, it is best to keep it to a minimum. Maximum reduction flight weight is one of the most important aircraft manufacturing principles, since any additional weight reduces maneuverability, flight time and payload.

Features of the choice of rotors

As you remember, the quadcopter is kept in the air by two pairs of rotors that rotate in opposite directions. The main characteristics of the rotors are pitch and diameter, an increase in which leads to increased energy consumption by the quadcopter motors.

Besides, step defines distance, which is overcome during one revolution screw. Briefly speaking, more propeller pitch assumes lower speed its rotation, but increases the speed of the aircraft, which, alas, increases energy consumption.

The ratio of screw diameter and pitch must be balanced. A smaller propeller pitch will produce more torque and reduce the power consumption of the motors. If you plan to use your quadcopter for aerobatics, you just need propellers with high torque. They will provide greater speed and less load on the energy source. In addition, lower pitch propellers increase flight stability.

Propeller moves the larger one in larger increments air volume, which can cause turbulence and lead to vibrations. If this happens, simply select lower pitch rotors.

As for the diameter of the main rotor, its efficiency is directly related to the area of ​​contact with the air. Thus, even a small increase in the diameter of the propeller leads to an increase in its efficiency. An example is the high swimming speed of swimmers with large hands and feet, who, however, expend more strength.

Propeller rotation with a smaller diameter it is easier to accelerate or stop (affects inertia). A smaller diameter propeller also means the motors consume less power. It is because of this that when building six- or eight-copters, rotors with propellers that are smaller in diameter than in quadcopters of comparable sizes are mainly used.

For large quadcopters With a large load capacity, it is recommended to use large-diameter rotors and an engine with increased torque to improve flight stability.

Motor and propeller: the agony of choice

• Observations and research. Start watching videos on YouTube. As a result, you not only drool over other people's quadcopters familiarize yourself with the designs, but also take a look at what motors and main rotors yours uses Colleagues By hobby. Important to use in your work someone else's experience, since it has already been paid for by outsiders.
• Delving into physics of the process And experiments. If you are a mathematically minded nerd and have extra money and couldn't find information about the propeller group that is really needed in your work, you can open a research program with different motor-propeller combinations. However, remember that research does not pay off immediately, so be prepared to waste time and money.

In the end - created and posted on the Internet

The eCalc online propeller calculator, known for such queries as: propeller calculator, rc calculator, rc calculator, is an effective tool for calculating the selection of an engine with a propeller for an aircraft model. This calculator will allow you not only to save the life of your engine, but also to increase its service life and also save battery life thanks to the ability to select the optimal parameters for cruising mode (optimal mode).

The calculator is online only and located at this address ECALC.CH. The main page (in English) offers a choice (of the calculator) by model type and choice of language:

• propCalc - calculator for airplane propellers
• xcopterCalc - calculator for copters
• fanCalc - impeller systems calculator
• heliCalc - helicopter calculator

Over the years, ECALC has reduced functionality for free users, so below are screenshots of how to bypass ECALC.CH restrictions, plus another link: http://rc-calc.com/ru/copter

For those who understand html without words, the description is for those who are new to it. We see that the AX-4008Q is inactive.

We press F12 in the browser (for example, in Chrome or Firefox) and we get into the “inspector”. Click on the arrow (marked with number 1 on the screen), then click on the selection window (of something, example with an engine) at number two on the screen and see that the line (under number 3) is highlighted.

Click on this line, there is an icon on the left - expand. We see the required engine in the list and see that there is a disable sign. We redo it similarly to other lines that work.

Example of the corrected line.

Over the years, ECALC has reduced functionality for free users, so here’s another link: http://rc-calc.com/ru/copter

Update: Due to the great interest in this particular part, the article on engines has been expanded and supplemented with information about such engine parameters as KV and XXYY dimensions.

And so, the engine, or in other words, the motor.

As you can see from the picture below, engines can come in a variety of sizes and have different looks and colors. Although there is a common feature that unites them - a cylindrical shape.

When we talk about motors for flying models, we usually mean brushless motors. These motors are very similar to conventional ones. They also have magnets and windings, but no brushes to transfer current from the motor contacts to the windings. That is why they are called brushless. These motors can be considered three-phase. Voltage is not supplied to the windings continuously, as with conventional DC motors, but at a certain frequency. This causes the moving part of the motor to rotate. Moreover, such motors can rotate much faster than usual, and at the same time not lose energy on the brushes.

What characteristics are important when choosing an engine? In addition to size, shape, color, etc. You should pay attention to two important characteristics of brushless motors:

• current consumption (measured in amperes A)
• Kv-rating

The first characteristic should be clear. The higher the motor power, the higher the current consumption, at the same supply voltage. The higher the current, the more lift the motor produces. The current depends on the engine speed and the load on it created by the propeller.

Kv-rating shows how many revolutions of its axis the motor will make in one minute (RPM) at a certain voltage. The formula is this: RPM=Kv*U

How to use these parameters when choosing an engine? First, the maximum current draw tells us which speed controller to choose (more on that later). Kv-rating is the equivalent of horsepower in a car. Few people understand what it is, but everyone knows that 100 hp is not enough, but 600 is cool. That's how it is here :)

Let's take a closer look at this parameter - KV. The comparison with horsepower, although correct, is not entirely clear when choosing an engine for your model. Imagine a sports car with 600 hp. Will she be able to go 300 km/h? I think yes. But can she do the same if 1t of weight is tied to her? No. And he won't even budge. Not because there is not enough power, but because the wheels will slip. What do we need to pull 1t of cargo? Tractor. The tractor may have less power and low speed, but large wheels and torque will allow us to pull our load. And so, we see that the same energy is needed for both the fast rotation of small wheels and the slow rotation of large wheels. In the case of quadcopters, a motor with a large KV is ideal for small, fast-spinning propellers (racing quadcopters), while a motor with a small KV is ideal for large drones with large propellers.

A typical racing quadcopter engine has a KV of 2100-2500, while for heavy vehicles that can lift several kilograms of their weight and the same amount of cargo - 200-900 KV. Racing models usually have propellers of 5-6 inches, while large aircraft designed for long flights and photography have 15-17 inches. Can you imagine what loads will be on the engine, propeller and everything else if a 15-inch propeller is spun to the normal speed of a small propeller? The KV rating of a motor is a very important characteristic when choosing, although it is not the only important parameter.

An important parameter when choosing a motor for a particular device is its lifting force (Trust). Lifting force can be measured in different units, although the correct one is Newton, but the convenient one is Kilogram. And so, a lifting force of 500 grams means that 4 engines will be able to lift 2 kg of weight, including themselves. At the same time, you need a power reserve. In total, we have the formula Force/1 Motor = (Copter Weight x 2) / 4. For a copter weighing 1 kg, motors with a minimum of 500 grams of lift are needed. It's simple.

Another characteristic of an engine is its efficiency. We won’t go into detail, but note that an engine with 70% efficiency spends 70% of energy on flight, and 30% on heating the universe, as my physics teacher said. The efficiency of the engine depends not only on the device itself, but also on other elements: propeller, battery, speed controller, weight, etc.

In addition to all this, engines also have physical parameters that are displayed in their dimensions. These are the motor height, diameter and number of winding coils. For example, Turnigy Multistar 5130-350 — This is a motor with a stator diameter of 51mm, a height of 30mm and a KV of 350. This is a large motor for large models. And this one - Scorpion M-2205-2350KV small but very good engine for racing quadcopters. It is 22 mm in diameter and 5 mm in height. Has a KV rating of 2350.

The engine itself cannot create lift; a propeller is needed. A propeller is a kind of converter of rotational energy of the engine shaft into lifting force.

The most important characteristics of a propeller are its size and the pitch of the blades. The size is usually indicated in inches, and everything is clear here. Pitch is also indicated in inches, and means how much the propeller would rise in one revolution around its axis with a given blade inclination if it were moving in dense matter.

A smaller propeller with a lower blade angle resists the air less, and therefore puts less strain on the engine, preventing it from using all its power. Accordingly, a very large propeller will put more stress on the engine and lead to overload. Thus, it is necessary to select propellers so as to fall within the permissible limits of the engine operating parameters and create sufficient lift. The standard propeller for an average quadcopter is usually a propeller with characteristics 8-11/4.5-4.7. For example, this site will help you calculate the parameters of the propeller (and more).

Also, don't forget that propellers come in two types of rotation: clockwise and counterclockwise. This is necessary so that half of the quadcopter’s engines rotate in one direction, and the other half in the opposite direction.

Soon we will look at several engines from the point of view of the influence of their characteristics on the parameters of the quadcopter and learn how to choose an engine for our tasks.

A very good article about choosing an engine and propellers in English is here.