This tutorial is designed to give you a basic understanding of multicopter motors and propellers. These instructions and recommendations will help you choose the motors and propellers you need for your quadcopter or any other Quadcopter.There will be differences between theory and reality. In different environments and different wind speeds, the battery life is also different.
Wondering where to start? Decide on the motor size first
First, you need to answer a few questions:
- What is the total weight of the quadcopter you plan to have?
- What are the dimensions of your quadcopter’s overall structure?
As far as the total weight of the quadcopter is concerned, you can only assume it in the initial stages, because you haven’t developed it yet. The total weight of course includes everything from the frame, FC, PDB, cables, motors, ESCs, batteries, payload (HD camera, gimbal, etc.) and other components. Remember that the total weight to start with is always a conservative approximation. When you finally decide on the final components to use in your quadcopter, you can always go back and update your total weight.
The maximum size of the frame can help you determine the best propeller size. These two important pieces of information will give you a good idea of the thrust required by the motors to lift the quadcopter into the air by using the finite size propellers.
2:1 thrust-to-weight ratio
A rule of thumb is that the robot should be able to provide thrust at least twice the weight of the quadcopter. Remember, this is the minimum amount of thrust the drone needs in order to be easier to maneuver while hovering in a position. If the motor is not able to provide the necessary thrust, then you may have difficulty controlling the device. Since the thrust can’t match the weight of the drone, your device may not even have enough power to take off.
To explain these things further, let’s consider this example. If we have a quadcopter with a total weight of about 1 kg, the motors should be able to produce a total thrust of at least 2 kg at maximum throttle, or 500 grams per motor in the case of a quadcopter.
In the case of drones being developed for racing purposes, the thrust-to-weight ratio may go further up depending on your requirements. It is not common for racing quadcopters to depict 8:1 or even 10:1 thrust-to-weight ratios. Quadcopters are definitely getting faster; acceleration is faster and cutting corners is much better. However, keep in mind that a high thrust-to-weight ratio will make it harder for the pilot to control the equipment, since a small throttle is enough to make the quadcopter circle.
If you wish to turn your quadcopter into a slow-moving platform for aerial videography and photography, we recommend that you choose a thrust-to-weight ratio of 3:1 or 4:1. Such a configuration will allow you to have precise control over the device and attach more payloads in the future. The extra payload can be a bulkier camera or extra batteries if you’re trying to extend your flight time.
Motor size and KV
Brushless motors in normal RC quadcopter can be identified by a 4-digit number – AABB. “AA” corresponds to the stator width, while “BB” indicates the stator height. The wider and taller the motor, the more torque it can produce.
KV is another key factor. It is the theoretical increase in rotor revolutions per minute (RPM) when the voltage is increased by 1 volt without any load. For example, when a 2300 KV motor is powered by a 3S LiPo (12.6 V) battery, the motor tends to spin at 28980 RPM. Keep in mind that we used some serios estimates just to elaborate.
However, when you connect the propeller to the motor, the RPM will definitely drop due to the increased drag. A motor with a higher KV produces more RPM, so the propeller spins faster. However, motors with lower KV produce lower torque. This is exactly why drones prefer to use heavier propellers, the motor has a lower KV value and the propeller has a lower KV value. You can always modify the KV value of a motor by increasing or decreasing the number of copper windings in the motor.
When selecting a motor and propeller for your drone, you need to strike the right balance of RPM and torque. When you connect a heavy propeller to a motor with a high KV value, the motor will try to spin the propeller very quickly, drawing more current and generating more heat in the process. This inevitably leads to overheating of the motor and shorting of the copper coils in the motor.
N and P
You may have come across symbols such as “12N14P”. The number before the letter N indicates the number of electromagnets in the stator, while the number before the letter P indicates the number of permanent magnets in the motor. Most motors on the market come in a 12N14P configuration. Some lower KV motors have more electromagnets and permanent magnets to help generate more torque. Such motors are usually at the high end of the price scale. This is great information, but not mandatory when buying a motor for your next quadcopter.
Frame Size ⇒ Propeller Size ⇒ Motor Size and KV
In most cases, just knowing the dimensions of the quadcopter’s frame allows us to determine the type of motor that is right for our project. This is because smaller frame size means smaller propeller size and therefore smaller motor and lower KV value. Nevertheless, we recommend that you review the motor thrust data to ensure that when installing the propeller you intend to use with your quadcopter, you are not drawing more current than the motor is rated for safely.
The table below has been tabulated to give you a simple idea and compiled with the assumption that you are using a 4S LiPo battery. There are many people who will use higher or lower KV motors than those provided in this table. Frame size refers to the wheelbase, which is the diagonal distance between the motors.
Voltage and Current Consumption
You have to keep in mind that voltage has a huge impact on the type of motor and propeller you choose for your quadcopter. When you apply higher voltage to the motor it will definitely try to spin faster and therefore draw more current from the battery. Also, it is very important to check the thrust data of the motor.
Read Motor Specifications
Motors have specifications provided by the manufacturer at the time of development. You should pay attention to the power, thrust, speed, etc. of the motor. in these specifications.
Comparison Between Motors
Once you have determined the size and KV of your motor, you still have a lot of options to choose from. Here are a few things you need to consider when choosing the best motor for your goals.
- currently drawn
- Weight – moment of inertia
The final decision comes down to your own preference; it basically comes down to how you want your quadcopter to perform. By instilling higher thrust, you gain more speed. At the same time, you need to make sure that the device is efficient enough; that is, it doesn’t draw more power than the hardware it’s installed on supports.
Also, keep in mind that your motor and propeller preferences may affect the batteries you use. If your motor is able to draw optimal current from the battery at 100% throttling, the battery must be equipped to support a discharge rate consistent with the required power. Also, you need to make sure the battery doesn’t overheat and discharge too quickly. In this regard, you can look at the C rating.
Another aspect that most people don’t pay much attention to is motor weight. This is an important factor in racing drones. In addition to affecting the quadcopter’s overall weight and weight-to-thrust ratio, it also affects the device’s moment of inertia. For example, when your quadcopter performs those midair stunts such as rolls and flips, it will take some time for your quadcopter to gain the necessary angular acceleration and move down to the target position. With heavier motors, it may take more time for the quadcopter to do this, thus giving you the impression that it is not as responsive as you would like it to be.
In fact, the whole game is about bringing much needed balance or areas where you want your quad to perform better at the expense of the other quad!
More Tips on Motor Efficiency
Drone RC aircraft perform better when they are as light as possible. This article explains how to strike the ideal balance between selecting a Li-Polymer battery for your multicopter. Battery and weight aren’t the only parameters that have a say in this complex equation when talking about overall power efficiency.
When choosing a suitable motor, in addition to the motor KV and thrust, we also need to consider the motor efficiency. It’s more or less similar to riding a bicycle. On a bike, when you go in a lower gear, you can move faster, but you also have to pedal faster while facing more resistance. Pedaling gets harder and harder while climbing increasingly steeper rocky terrain. There will come a day when, despite how hard you are pedaling, you will get slower and slower. This is the little bit you will lose in terms of efficiency.
The same process is also relevant for brushless motors. The more efficient it is, the better it is for your quadcopter. A motor that is 70% efficient means it will generate 70% of the power and dissipate 30% of the energy as heat. On the other hand, a motor that is 90% efficient will produce 90% of the power and only 10% of the energy will be lost as heat.
If you’re using a less efficient motor, it will cause more heat loss, reducing flight time. Also, you won’t get enough thrust at full throttle. What’s more, you won’t get the necessary response from the device due to the inefficiency of the motor. The motor will reach its target RPM at longer intervals, which will negatively affect stability and responsiveness.
What other manufacturers don’t tell you
- Best propeller
Response refers to the ability of a motor to change its revolutions per minute. The easiest way to measure this is to determine the time it takes the motor to go from zero RPM to optimal RPM. This in turn affects the responsiveness of the motor.
If you are able to explore the data mentioned below elsewhere, you will surely be able to identify the motor you need for your quadcopter.
Motor features you may be interested in
- Solid/hollow shaft
- Magnet type (N52, N54)
- Arc magnet
- Smaller air gap
- Solder tabs on the motor
- ESC integration
- Cooling design
CW and CCW motors
Driveshaft thread rotation is the basic difference between CW and CCW motors. The actual goal is to use several CW motors and CCW motors on the quadcopter so that when the motors spin, all four prop nuts are seated in their designated slots. It doesn’t really matter which one you should choose, as they are almost similar to each other, the only difference being the drive shaft threads. But we recommend that you use all motors with the same thread to avoid confusion with all the different prop nuts.
The propeller is responsible for creating the necessary thrust by spinning and stirring the surrounding air. The more air stirred in the surrounding environment, the more thrust is generated.
Basics – Size/Spacing
Propeller specifications are generally represented by 4 digits, the first two digits represent the diameter, and the last two digits represent the pitch. Take the 1060 paddle as an example, 10 means the diameter of the paddle is 10 inches, and 60 means the paddle angle (pitch, 6.0 inches, which is 152.4mm).
The same motor, with different KV values, use different propellers, each motor will have a recommended propeller. Relatively speaking, if the propeller is too small, the maximum thrust cannot be exerted; if the propeller is too large, the motor will overheat and demagnetize the motor, resulting in a permanent decline in motor performance.
Effect of Prop Size and Spacing
When choosing propeller size, length and pitch, you need to strike the right balance. Generally, a lower pitch propeller will spin faster at a higher RPM. The motor doesn’t need to provide more energy to spin the propeller, so less current will be drawn. If you want to perform incredible mid-air stunts, you should choose a low-pitch propeller to provide higher acceleration; thus consuming less system power. This will also have a positive effect on the stability of the aircraft.
On the other hand, a propeller with a higher pitch will move more air, which in turn will destabilize the drone and create a propeller wash. More thrust will be produced at the cost of drawing more current from the battery; giving you more speed.
A propeller with a smaller size will be easier to stop and accelerate. Conversely, a larger propeller takes longer to change its rpm due to its inertia.
Propellers are made of a variety of materials, including plastic, carbon fiber, wood, and more. Each type of material enables unique functions and properties, such as carbon fiber and wooden propellers are a bit stiffer and provide smooth flight. On the other hand, propellers made of plastic are more durable and reliable. You can read this article for more details.
Another important parameter that is critical to the performance of a quadcopter is the shape of the propellers. The most notable difference between propellers of different shapes and sizes is their tips: pointed nose, bull nose (bull nose), and hybrid bull nose (HBN). Propellers of the same size and pitch are most efficient when pointed and producing less thrust. A bullnose propeller produces more thrust, but at the same time draws more current from the battery. This is mainly due to their greater surface area than those with small tips. A hybrid bullnose propeller is a hybrid of the two types of propellers discussed above.
Number of blades
Two-bladed propellers are the most commonly used propellers. Drone racers and FPV Drones have taken to three-blade propellers. There are also four-blade and six-blade propellers on the market. In fact, the more blades a propeller moves, the more surface area it has and therefore the more thrust it can generate. However, in this case, the propeller will draw more current from the battery, resulting in less efficiency.
5200mAh means that it can be discharged for 1 hour with a current of 5.2A. Of course, that’s all we understand. The actual discharge time needs to refer to the relevant technical parameters provided by the battery manufacturer.
30C battery refers to the discharge capacity of the battery. For a 30C battery, the maximum continuous discharge current is: battery capacity X discharge C.
For example: 5200MA, 30C battery, the maximum continuous current is =5.2X30=156A (ampere).
If the battery is operated with a current of 156A or above for a long time, the life of the battery will be shortened.
For the single-chip voltage of the battery, it should be 4.15-4.20 when fully charged (3S battery corresponds to 12.6V), and the minimum voltage after use is above 3.7 per chip (3S corresponds to 11.1V, remember not to over-discharge), long-term use The best storage voltage is 3.9 (3S corresponds to 11.7V).
Which rack should I choose? Machines under 2kg can choose fiberglass racks; machines over 2kg can definitely use 3K carbon fiber, of course, the price is not cheap; you can also make your own racks if you have good hands-on skills.
What size rack should I use?
There is a calculation formula for this, and the calculation formula is as follows: Frame wheelbase = (inches of paddles*25.4/0.8/root 2)*2. Propeller size (inches) = (frame wheelbase/2)*root 2*0.8/25.4.
The test is for reference only
It is critical to go through a motor thrust test and determine which propellers work well with the motors you plan to choose for your quadcopter. Propellers perform differently when combined with two different types of motors.
Even propellers of the same size and pitch tend to perform differently from different materials and from different manufacturers. You can see a comparison of 5030 propellers from different manufacturers.
However, these tests are performed in a static environment. Therefore, they do not represent the actual performance of the motor/propeller under real-time conditions where weather conditions and other factors play a significant role. One of the most notable differences between static testing and live flight is motor thrust, which is typically 5% to 10% lower in live scenarios than under test conditions.
How to choose the Motor and Propeller of the Quadcopter