How to Choose FPV Drone Motors
Let's dive into the fascinating world of FPV drone motors! In this comprehensive guide, we'll cover the ins and outs of motor construction, design features, and the factors that can affect a motor's performance and efficiency. With a solid understanding of the design decisions involved, you'll have the knowledge you need to choose the ideal motor for your next drone build.
Where should I start?
If you are new to the FPV scene, we highly recommend you read our FPV drone beginners guide first to learn the basics: Step-by-Step Guide
Before you choose a motor, it's important to have at least a rough idea of the size and weight of the drone you want to build. We'll walk you through the process of determining motor size based on the drone you want to build. However, if you're focused on building a 5-inch FPV drone, feel free to skip ahead to the "Motor Size" section.
The most important factors to consider include:
- engine weight
- force (thrust)
- Efficiency (grams per watt)
- Torque and reaction (speed changes)
Brushless vs. Brushed Motors
In the RC world, there are mainly two types of motors: brushless and brushed. In general, we prefer brushless motors because they are more durable and powerful, while brushed motors are often used in toy drones because they are cheaper to manufacture. In this guide, we will focus exclusively on brushless motors, which are the first choice for most FPV drones.
Estimating drone weight and frame size
When considering the total weight of your FPV drone, make sure to include all components: frame, FC, ESC, motors, propellers, RX, VTX, antenna, ESC, LiPo battery, GoPro and so on. Although it doesn't have to be 100% accurate, an accurate estimate is essential. It's better to overestimate the weight and have more power than to underpower and struggle to take off.
By determining your frame size you can determine the maximum allowable propeller size.
Determination of thrust requirements
To calculate the minimum thrust required for your motor-propeller combination, you will need the estimated total weight of your drone. As a general rule of thumb, the maximum thrust of all motors should be at least twice the total weight of the quadcopter. Insufficient thrust can result in poor control response and difficulty taking off.
For example, if you have a 1kg drone, the total thrust produced by all motors at 100% throttle should be at least 2kg. That's 500g of thrust produced by each motor for a quadcopter. Of course, having more thrust available than you need is always a bonus.
For racing drones, the thrust-to-weight ratio (or power-to-weight ratio) should be significantly higher than in the example above. Ratios of 10:1 or even 14:1 are not uncommon. For acro and freestyle flying, we recommend a ratio of at least 5:1.
A higher thrust-to-weight ratio gives a quadcopter more agility and acceleration, but can make it harder to control, especially for beginners. Even the slightest throttle input can "shoot the quad into orbit like a rocket." Pilot skills and experience play an important role in mastering this power.
Even if you only want to fly a slow and stable aerial device, you should aim for a thrust-to-weight ratio of more than 3:1 or even 4:1. This not only provides better control, but also leaves room for additional payload.
Connecting a brushless motor
To drive a brushless motor, you need an ESC (electronic speed controller). Unlike brushed motors, which have only two wires, brushless motors have three wires. You can connect these wires to the ESC in any order. To reverse the direction of rotation, simply swap two of the three wires. In addition, it is possible to reverse the motor direction via software settings.
Engine Size Explained
The size of the brushless motor is typically specified in RC by a four-digit number – AABB:
“AA” stands for the stator width (or stator diameter)
“BB” stands for the stator height, both measured in millimeters
The stator is the stationary part of the motor and consists of "poles" wrapped with copper wires (windings). These poles are made of several layers of thin metal plates laminated together, with a very thin layer of insulation in between.
Let’s break down the key components of an engine:
Motor stator:
The stationary part of the motor consists of several metal coils. The coil wire is enameled to prevent short circuits as it is wound in several loops. When an electric current flows through the stator coils, it creates a magnetic field that interacts with the permanent magnets on the rotor, creating rotation.
Magnets:
Permanent magnets generate a fixed magnetic field. In FPV motors, they are attached to the inside of the motor bell with epoxy resin.
Engine bell:
The motor bell housing serves as the motor's protective housing for the magnets and windings. Some motor bell housings are generally made of lightweight metals such as aluminum and are designed like miniature fans to direct more airflow over the motor windings, providing additional cooling while the motor is rotating.
Motor shaft:
The shaft connected to the engine bell is the working element of the engine that transfers the torque generated by the engine to the propeller.
Increasing the stator width or height increases the stator volume, the size of the permanent magnets, and the size of the stator electromagnetic coils. This increases the overall torque of the motor, allowing it to spin a heavier propeller faster and produce more thrust (at the cost of higher current draw). However, the downside of a larger stator is that it is heavier and less responsive.
Comparison of higher and wider stators
Wider motors have greater inertia when rotating because the mass of the motor is further from the axis of rotation and more energy is required to change speed. As a result, wider and shorter motors tend to respond less quickly than narrower and taller motors, even if they have the same stator volume and produce the same torque. Wider and shorter motors also have smaller magnets on the motor bell housing, which can reduce the motor's performance.
However, wider motors offer better cooling due to the larger surface area on the top and bottom. Temperature is critical to motor performance. As a motor heats up, its ability to generate magnetic flux decreases, affecting efficiency and torque production.
Essentially, the width and height of a motor stator represent a balance between responsiveness and cooling. The decision depends on your flying style. For example, for slow cinewhoops with a heavy GoPro, you may need motors with wider stators for better cooling. For fast and responsive racing or freestyle drones, taller stators may be preferable.
Wider stators also allow for larger bearings, which can improve efficiency, smoothness and durability.
Bigger stators are not always better. For example, 2207 motors can handle typical 5" propellers, but using much heavier 2506 motors with the same KV may not provide significant benefits as they would produce the same thrust with the same propellers or even offer worse response due to weight. To improve performance without adding weight, consider higher KV motors. However, the 2506 motor in this example would probably work better for 6" propellers than the 2207 due to the increased torque requirements.
Engine torque:
High torque motors provide rapid speed changes and faster response times, resulting in less propeller wash and faster responses.
Engine torque depends on several factors, including:
- Stator size (volume)
- Materials: type of magnets and quality of copper windings
- Motor design: such as air gap, number of poles, etc.
Since FPV motors have had similar specifications and designs in recent years, stator size is the easiest way to quantify torque.
The stator size can be calculated using the formula for the volume of a cylinder:
Volume = pi x radius^2 x height
For example, the stator volume of a 2207 motor is:
pi x (22/2) ^2 x 7 = 2660.93
The larger the stator volume, the more torque a motor can produce. Compared to a 2306 motor with a volume of 2492.85, a 2207 motor has more torque.
When selecting a motor, compare the volume and weight of the motor stator. A lighter motor with the same volume is preferable, other things being equal, so why not choose the largest motor available? The answer lies in the weight. Motors with larger stator volumes are heavier, so it really depends on the application.
For example, lightweight drones don't need much throttle to stay airborne, making more torque available. Combined with lower pitch propellers, motors can spin them with less torque. In this case, motor torque requirements are low, allowing the use of smaller, lighter motors that keep overall weight down.
A lower-powered motor (with less torque) is preferred only when smoothness takes priority over responsiveness. High-torque motors can change speed so quickly that they feel jerky and less smooth. They can also generate more voltage spikes and electrical noise in the power system, potentially affecting gyro performance and overall flight performance if noise filtering is not optimal, causing oscillations.
KV
"KV" indicates the number of revolutions per minute (RPM) a motor will spin when 1V (one volt) is applied, without a load (such as a propeller) attached to the motor. For example, a 2300KV motor powered by a 3S LiPo battery (12.6V) will spin at about 28,980 RPM (2300 x 12.6) without any propellers attached. KV is typically a rough estimate provided by the motor manufacturer.
When a propeller is mounted on the engine, the RPM drops dramatically due to drag. Higher KV engines try to spin the propeller faster, producing more thrust and power (while drawing more current). Larger propellers are usually paired with low KV engines, while smaller, lighter propellers work better with high KV engines.
The KV of the motor is determined by the number of copper wire windings in the stator. Generally, a higher number of turns will decrease the KV of the motor, while a lower number of turns will increase it. The magnetic strength of the magnets can also affect the KV, with stronger magnets increasing the KV.
When a high KV motor is combined with an overly large propeller, the motor will attempt to spin quickly as it would with a smaller propeller, requiring more torque. This increased torque requirement results in more current draw and heat generation. Overheating can cause the motor to burn out, as the coating on the coil can melt and cause electrical shorts in the motor. For this reason, a higher KV motor is likely to run hotter than a lower KV motor of the same size.
KV also affects the current and voltage limits of a motor. Higher KV motors have shorter windings and lower resistance, which reduces the maximum voltage rating and increases the current draw for the motor-propeller combination. However, the motor's product page will list the allowable voltage and maximum current.
It is recommended to choose the correct KV motors for the battery voltage you plan to use.
KV vs. torque constant
The KV value of the motor does not directly affect torque, but it does affect the torque constant. The torque constant of a motor indicates how much current is required to produce a certain torque. KV has no effect on the actual torque produced; factors such as magnet strength, air gap and coil resistance have a much greater effect on torque production.
Higher KV motors have a higher torque constant, meaning they require more current to produce the same torque as a lower KV motor. To produce the same torque, the higher KV motor requires more current, which results in additional losses in the ESC, battery, and wires. Additionally, more heat builds up in the motor due to the higher current, and less magnetic flux is produced. Overall, a higher KV motor is less efficient if you are flying at the same speed as the lower KV motor.
Therefore, it's a good idea not to overdo it with KV; try to keep it moderate. This is especially important when building a long-range rig where efficiency and flight time are paramount.
engine assembly
Common mounting patterns (hole spacing) for 22xx, 23xx and 24xx motors are 16 x 19mm and 16 x 16mm. Modern 5" FPV drone frames should support both patterns. The mounting holes of these motors use M3 screws. Use screws with a thread length 2mm longer than the thickness of the arms. For example, for 5mm arms, use 7mm screws and for 6mm arms, use 8mm screws.
poles and magnets
When you're looking for motors for your FPV drone, you may come across specifications like "12N14P" printed on the packaging. Here's what these numbers mean: The number before the letter "N" indicates the number of electromagnets (poles) in the stator, while the number before "P" represents the number of permanent magnets in the bell.
Different motor sizes have different numbers of poles; for example, 22XX and 23XX motors generally have 12 poles and 14 magnets.
The number of poles has a direct impact on motor performance. Having fewer poles allows you to put a higher percentage of iron in the stator, resulting in more power output. However, a higher number of poles results in a more uniform magnetic field. This in turn makes the motor run smoother and gives you finer control over the rotation of the bell.
In short:
- More poles = more consistent performance
- Fewer poles = more power
Since FPV drone motors are typically three-phase, the pole configuration must be a multiple of 3 (i.e. 9, 12, 15, 18, etc.). This is due to the presence of three wires connected to the motor. Therefore, the pole count is not easily changed and is not a critical factor in choosing motors, especially for FPV drones. However, you should pay attention to the pole count as you will need to enter this number into Betaflight.
motor windings
The number of copper windings or "turns" on a stator pole determines the maximum current a motor can draw. At the same time, the thickness of the wire affects the motor's ability to handle current before reaching the point of overheating.
Put simply, fewer turns mean less resistance, which leads to a higher KV. However, this also leads to a reduced electromagnetic field on the stator and therefore lower torque.
On the other hand, if the coil has more turns, the increased amount of copper creates a stronger magnetic field at the stator pole, producing more torque. But there's a catch: the longer wires and higher resistance cause the KV of the motor to drop.
So how do manufacturers address these challenges when increasing the performance of FPV drone motors? The answer lies in increasing the number of turns while using thicker copper wires. This ingenious approach effectively reduces winding resistance, improving performance without sacrificing efficiency and torque. In addition, a motor with a larger wire gauge can handle high currents without burning out.
However, it is important to note that the use of thicker wires and additional windings results in a heavier motor. In addition, the winding takes up more space, which requires a larger stator. This is why we are seeing the emergence of larger and heavier motors on the market, which also explains their higher power.
Multi-strand vs. single-strand windings
There are basically two options for motor windings: single-strand and multi-strand. Each has its own advantages and disadvantages, making it suitable for different applications.
Single strand windings use thicker wires that handle heat better, making them ideal for demanding flights that use a lot of power (e.g. racing, acro, freestyle, etc.). However, the thicker wires result in larger gaps between them, which limits the number of wires that can be wrapped around the stator.
In multi-core windings, on the other hand, a single, thicker wire is replaced by several smaller ones. These thinner wires do not conduct heat as efficiently and are more susceptible to physical breakage.
Despite these limitations, multi-strand windings may offer better performance than single-strand windings because they are more densely packed around the stator and have smaller gaps between wires, resulting in a stronger magnetic field. This can lead to improvements in power and efficiency. However, multi-strand wires are generally more difficult to achieve the same cleanliness as single-strand wires. Added to this is the fact that there are more layers of insulation between the multi-strand coils, resulting in more air gaps between wires, which may offset the above benefits.
It is important to note that the cleanliness of the windings plays a crucial role both aesthetically and electrically. Messy windings with numerous wire crossings will result in less efficient magnetic fields because the wires do not cross the stator perpendicularly. So when evaluating motor windings, do not forget the importance of neat and well-organized winding work.
Finally, multi-strand wires can overheat more quickly than single-strand wires, which affects the motor's raw power and efficiency. Overall, the single-strand winding is likely to be the better choice in practice.
camp
Motor mounts may not be a commonly discussed topic due to the lack of information online, but they play a crucial role in the performance of your FPV drone. Let's take a closer look at the basics of motor mounts.
The size of a bearing is determined by the difference between its outside and inside diameters, not the diameters themselves. Wider bearings can accommodate larger balls (or marbles) within them. While larger balls offer greater durability and crash resistance, smaller balls offer more stability and smoothness at high speeds and rpm.
Some motors are marketed with "ceramic bearings" that use ceramic balls instead of steel balls. These bearings, while smoother, are also more prone to breakage.
The inner diameter of the bearing also determines the size of the shaft that can be used. A 9 mm x 4 mm bearing offers a good balance between durability and smooth running.
Popular bearings used in FPV drone motors include Japanese brands such as NSK, NMB, and EZO. Although EZO bearings are often touted as the best bearings, it is difficult to quantify their superiority over other brands. In addition, it is important to consider the possibility that manufacturers are using counterfeit products instead of genuine ones.
Choosing the right motor size for your drone
To determine the ideal motor size for your drone, follow this order: Frame size => Prop size => Motor size.
Determining the frame size will help you estimate the appropriate motor size. The frame size limits the propeller size, and each propeller size requires a different motor speed to efficiently produce thrust - this is where the motor CVD comes into play.
Also, make sure the motors produce enough torque to turn the propeller you choose. This consideration relates to stator size. Generally, a larger stator size and higher KV will result in higher current draw.
Consideration of voltage and current consumption
It is crucial to understand the role of voltage in choosing your motor. If you use a higher voltage, your motor will try to spin faster, which will result in a higher current draw. Pay attention to the thrust your motors produce and the current they require.
Once you know exactly the current draw of your motor and propeller combination, you can confidently choose the right ESC for your drone. Keep in mind that the ESC should be able to handle the maximum current draw of the motor without exceeding its limits to ensure safe and reliable operation.
How to evaluate engine performance
Once you've narrowed down the motor size, you'll likely still have several options to choose from. Consider the following factors to determine the best motor for your specific needs:
- thrust
- Efficiency and power consumption
- Weight
Ultimately, your choice of engine will be influenced by your intended use, your flying style and the performance characteristics you desire.
thrust
When it comes to choosing a motor for your FPV drone, thrust is often the first thing that comes to mind. After all, it's the power that propels your drone through the air and allows it to perform those impressive flight maneuvers.
While higher thrust will result in faster acceleration, it's important not to overlook other factors such as current draw and efficiency. Choosing a motor-propeller combination that requires excessive current can place excessive strain on your batteries and potentially shorten their lifespan.
If your drone consumes a lot of power at high speeds, it is important to make sure that your battery's maximum discharge rate is up to the task.
While thrust is undoubtedly an important aspect to consider when choosing a motor for your FPV drone, it is important to weigh it against the other factors listed below.
engine weight
Motor weight is an often overlooked factor when choosing FPV drone motor, but it plays a crucial role, especially in high-performance drones such as racing drones and freestyle drones.
Motors are mounted at the four corners of the frame, meaning they have a significant impact on the responsiveness of the quadcopter. Heavier motors increase the angular moment of inertia and require more torque (not just thrust) for the motors to change the drone's attitude.
When your quadcopter performs flips and rolls in real-world flight scenarios, it needs time to gain angular acceleration, reach the desired position, and then come to a stop. Heavier motors take longer to reach the required angular velocity and decelerate, making the drone feel less responsive. This is especially important if your flying style involves quick changes in direction, such as freestyle and racing. For those who focus primarily on driving in a straight line, such as movie cruisers, motor weight may not be as important.
efficiency and power consumption
When choosing an FPV drone motor, it's important to consider the motor efficiency, which is typically calculated by dividing the thrust by the power at 100% throttle, measured in grams per watt (g/w). A higher number indicates a more efficient motor.
But don't just look at efficiency at the top end. Analyze efficiency throughout the throttle range, especially the part of the throttle range where you primarily fly. Some motors may be efficient at lower throttles, but lose efficiency as they draw higher current and approach their limits.
Another useful metric for measuring efficiency is grams per amp (thrust/current).
In general, as thrust increases, so does the power required to produce it. Therefore, motors with high thrust and low current draw are preferable. Inefficient motors may produce too little thrust or draw too much current.
Each engine responds differently to different propellers. Choosing the right propeller is critical to achieving the balance between thrust and efficiency.
Keep in mind that efficiency and current draw also influence your choice of battery. An efficient motor with a high current draw can overload your battery and cause voltage drops, so it's important to find the right balance to optimize your drone's performance.
Performance Factors for Advanced Engines
Some properties of drone motors are not explicitly mentioned by the manufacturers and can only be determined through more detailed technical tests.
Here are some advanced factors to consider when choosing an engine:
- torque
- reaction time
- temperature
- Vibration and balance
engine torque
Torque is the force responsible for turning the propeller and determines how quickly an engine can increase and decrease its speed. In other words, it measures how easily an engine can move the rotor, the propeller and, most importantly, the air.
The torque of an engine has a significant impact on the performance of your quad, especially its precision and responsiveness during flight. A high torque engine will provide faster response due to faster speed changes. Increased torque can even reduce propeller scavenging.
In addition, high torque allows the use of heavier propellers (albeit at the cost of higher current draw). If a low torque motor is tasked with turning a propeller that is too heavy for it (also known as over-propping), the motor will struggle to generate enough power to reach the desired speed, resulting in poor efficiency and overheating.
However, high torque motors have a potential disadvantage: oscillation. These motors can change speed so quickly that they actually amplify errors (in the flight controller's PID loop), causing oscillations that can be difficult to eliminate even with PID and filter tuning.
The torque is directly influenced by the stator size, whereby in general a larger stator means more torque.
Factors that can increase torque include:
- Stronger magnets
- Minimizing the air gap between permanent magnets and stator, for example by using arc magnets
- Thinner stator sheets
Another advantage of high torque engines is their greater tolerance to larger propeller pitches and sizes, allowing them to perform better with a wider range of propellers. However, using lighter propellers can also be beneficial, as speed changes occur more quickly.
reaction time
Motor response time is closely related to torque, with high torque motors typically having faster response times. A simple way to measure response time is to estimate how long it takes for a motor to reach 0 maximum speed.
Response time is greatly affected by the weight and pitch of the propeller you choose. Keep in mind that atmospheric conditions can also play a role. For example, at lower altitudes the air is denser, meaning the propeller has to move more air molecules to generate thrust. At higher altitudes your propellers will spin faster and respond more quickly to throttle changes, but the overall thrust will be reduced because the propeller has fewer air molecules to interact with.
temperature
Temperature plays a crucial role in the performance and longevity of brushless motors. The magnets used in these motors have a weaker magnetic field at higher temperatures, which can lead to faster demagnetization and affect the life of the motor.
Over-assisting your motors or applying too much wide open throttle can cause your motors to overheat. This in turn can affect the performance of the motor and magnets over time, so motor designs that allow for better cooling often result in longer life.
vibration
Vibrations from engines can have several undesirable consequences for the performance of your quad.
An engine with poor balance or poor build quality can produce vibrations that can affect your PID controller. As the vibration frequency changes at different throttle levels, tuning your quad can become increasingly difficult.
Additionally, a motor subject to vibration will produce more electrical noise than a quietly running motor. This electrical noise can interfere with your gyro sensor, further affecting flight performance and potentially even affecting the quality of your FPV video if your FPV system is powered directly by the drone's battery.
To mitigate vibration problems, most flight controllers come with soft-mount solutions such as rubber grommets that offer significant improvements. However, it is important to remember that damaged, bent or unbalanced propellers can also cause problematic vibrations. Check your propellers regularly and replace them when necessary to maintain optimal performance.
Main Features of FPV Drone Motors
Motor performance can be affected by many factors, making it a complex and somewhat controversial topic. Motors with the same stator size and KV can have different thrust, current draw and response times, even when using identical propellers. Both design and material selection can significantly affect performance.
In this section we examine various engine design features that can contribute to improved performance and change the characteristics of the engine.
motor shaft
The motor shaft is an integral part of a brushless motor as it is responsible for securely attaching the propeller. Most brushless motors designed for 3″, 4″, 5″ and 6″ propellers have M5 shafts with a diameter of 5mm.
The design of the motor shaft has evolved over time to ensure better performance and durability:
1. Solid aluminum shafts:
In the past, motor shafts were made from solid aluminum rods. Although they were lightweight,
these shafts are less stiff and more prone to bending.
2. Hollow titanium shafts:
To solve the problems with solid aluminum shafts, manufacturers began to use hollow titanium shafts. These
Shafts offered similar weight savings, but were significantly stiffer and more rigid. Drilling a hole through the center of the
However, the titanium shaft increased production costs.
3. Hybrid waves:
More recently, some engine manufacturers have developed a hybrid shaft design in which a steel rod is inserted into the hollow titanium shaft
This innovative design combines the rigidity and strength of steel with the lightweight properties of titanium, ensuring
for superior performance and durability.
magnet type
Magnets used in brushless motors are rated according to their magnetic field strength, e.g. N50, N52, N54, with higher numbers indicating a stronger magnetic field. For example, a motor with N52SH magnets is better than one with N50SH magnets.
A stronger magnetic field theoretically allows the motor to generate power more efficiently, resulting in higher torque and faster response times. However, a motor with a stronger magnetic field will typically produce more notches when turned by hand. This is not necessarily a good thing, as it indicates a less consistent magnetic field, which can result in a less consistent motor. You may notice that some motors feel "jaggier" than others when turned by hand. This reflects the strength of the magnets. Stronger magnets will make the motor more unsettled.
It is also important to note that magnets can lose their magnetic power at high temperatures, which can affect motor performance. To solve this problem, motor manufacturers often use N52H magnets, which are designed to withstand high temperatures. Some motors even use N52SH magnets, which are believed to be able to withstand even higher temperatures.
Finally, it is not uncommon for magnets to come loose in accidents or due to vibrations. To fix this problem, you can use Loctite 438 to glue the magnets back into the bell housing.
Curved magnets
The use of magnets, also called arc magnets, is a technique that allows magnets to be brought closer to the stator, creating a smaller and more uniform air gap. This in turn ensures better performance of the motors.
With bent magnets, the strongest magnetic point of each pole is no longer on the surface of the magnet, unlike traditional, non-bent magnets. The epicenter of the field of the pole on the outside of the curve is below the surface of the magnet, and the epicenter of the pole on the inside curve is actually above the surface, balancing the magnetic fields of the permanent and electromagnet, bringing them closer together.
In addition to the shape of the magnets, some manufacturers test mini quad motors with magnets of different thicknesses and have found that even a slightly thinner magnet (and therefore a weaker magnetic field) can make a noticeable difference in performance.
air gap
"Air gap" in a motor refers to the distance between the permanent magnets and the stator. The magnetic force decreases nonlinearly with distance, so reducing the distance between the two will significantly increase the performance of the motor. A smaller air gap not only makes the motor more powerful, but also improves torque and responsiveness.
The downside of a narrower air gap is higher current draw and lower efficiency. There are also durability concerns. If the motor bellhousing is subjected to any kind of impact and becomes misaligned or shifted, the magnet can run into the stator and eventually break.
stator laminations
A lamination is the thickness of the individual metal sheets stacked in the motor stator. The thinner lamination allows more layers of stator plates to be stacked to achieve the same height of the motor stator.
In general, thinner stator laminations are better for motor performance. They help reduce a phenomenon called eddy current, which generates heat in a changing magnetic environment. Thinner laminations mean less energy is wasted on generating eddy currents, resulting in more efficient and powerful motors.
lamination of the motor stator
C-clip vs. screw on the bottom of a motor shaft
In general, bolts are easier to remove and are more user-serviceable than C-clips or E-clips. However, bolts have a higher risk of being over-tightened, which can bind the shaft and make it difficult to turn the motor.
On the other hand, there have been reports of C-clips popping off during flight, which can cause the engine bell to fly off and lead to a crash. While screws may seem like the safer option, they are not immune to this problem.
aluminum alloy
The metal used for the motor bell and motor base determines the durability of the motor. There are two common types of aluminum alloy used in FPV motors: 7075 and 6082. The number denotes the different series of aluminum alloy grades and the chemical composition.
In short, 6082 is more ductile and malleable, while 7075 is stiffer and can withstand impact better. 6082 was used back in the days before 2016/2017, but 7075 is the most common in modern engines and is considered more impact resistant.
Unibell
There are two types of bell designs: the two-piece bell design and the unibell design.
The two-piece bell housing design consists of a machined aluminum upper section and a steel flux ring underneath, a traditional and widely used design in engines.
The Unibell design consists of an aluminum bell that extends over a steel flux ring - like a thin protective shell that surrounds the steel flux ring.
The one-piece construction of the Unibell design adds a slight weight to the motor over the two-piece bell design, but improves durability and reduces the risk of the motor bell sliding off - a common problem with some two-piece bell designs. Motors with a two-piece design can experience a hard impact that can cause the flux ring to separate from the top of the bell, rendering the motor unusable. However, this is almost impossible with the Unibell design due to the large adhesive surface that ensures a tight and secure connection between the two components.
Despite the slight weight penalty, the extra durability offered by the Unibell design justifies the cost in my opinion. After all, a negligible increase in weight results in a significant increase in load capacity, a trade-off that is worth it.
river ring design
A flux ring is the round steel ring inside the bell that contains the magnets. The bell is usually made of aluminum, while the flux ring is made of steel because it has to respond to magnetic field lines.
The latest flux ring design is a custom shape instead of the usual round shape, which can help direct more magnetic field lines back into the motor and improve torque.
O-ring
The O-ring under the inside of the engine bell housing is a great feature of an engine.
The O-ring acts as a buffer/cushion and absorbs some of the shock from physical impact. This can help maintain the smooth running of the bearing over a longer period of time and potentially extend the life of the motor. The additional protection provided by the O-ring can also reduce the need for maintenance and the frequency of parts replacement, providing both economic and practical benefits to users.
floor design
When it comes to engine base design, there is the more traditional "closed bottom" approach and the newer "bare bottom" style. Both designs have advantages and disadvantages.
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engine with bare bottom (open engine base)
engine with closed bottom
The "closed bottom" design means a stronger base, but the "bare bottom" tends to be lighter as the excess material is removed. The weight saving is about 2g.
Closed-bottom engines are less likely to have dirt build up in the bell housing, whereas open-bottom engines are easier to remove.
With the bottom exposed, you can clearly see how far the screws go in, and there is less risk of shorting the motor winding if the screws are too long. (This often happens to beginners with closed-bottom motors.)
With engines with a free bottom, dirt can easily get into the engine, but it is also easier to clean
However, the closed base provides better strain relief for the wires in the event of impacts and stretching.
Silver-plated copper wires
Both silver and copper are known for their exceptional conductivity. However, because silver is a larger atom with more inner electron shells, it holds its outermost electron very loosely. This means that it can dissociate its electrons more easily, allowing them to move more freely through the metal to transport heat and electricity. This makes silver an even better conductor than copper.
By coating the outside of copper wire with silver, you improve its electrical and thermal conductivity, both of which have a positive effect on motors.
However, silver-plated copper wires are much more expensive than regular copper wires, which is why they are not very common in inexpensive motors.
PoPo technology
The “Pop on Pop off” system is basically a motor shaft with a spring-loaded bearing for quickly installing and removing props.
Other properties
- solder lugs
- ESC integration
- Cooling design
Motor manufacturers are constantly experimenting with different designs and levels of hardware integration, which has led to advances in cooling and even integration of the ESC into the motor. Personally, I think solder tabs on the motor can be useful. They allow the use of a lighter cable to save weight in applications where less amplification is required. They should also be easy to repair if the wires get snapped, which can often mean the end of a typical design motor.
CW and CCW drone motors
You will rarely see brushless motors labeled as CW (clockwise) and CCW (counterclockwise).
This does not indicate the direction the motor rotates. Brushless motors can rotate in either direction. This label distinguishes the direction the motor screw is screwed in. This is done so that as the motor rotates, the torque from the propeller pushes the motor nut to be tightened instead of loosened. This will prevent your props from loosening and falling off during flight. This means you will need two of each for your 4-motor layout in the standard Betaflight rotation.
- Front left: CW
- Front right: CCW
- Rear left: Counterclockwise
- Rear right: CW
To determine if you have the correct threaded motor, simply hold the support nut on the shaft and then start turning the motor by hand in the direction you want it to turn. If the nut tightens then you have the correct nut :)
Personally, I prefer to have the same threads on all my motors so I don't get confused with the different propeller nuts. If you need to replace a prop nut at the hardware store, finding a CCW threaded nut (or, more commonly, a "left-hand threaded nut") can be a real headache. Prop nuts these days are lock nuts (with rubber inside) that hold relatively well when tightened and don't come off easily.
Let’s break down the key components of an engine:
Motor stator:
The stationary part of the motor consists of several metal coils. The coil wire is enameled to prevent short circuits as it is wound in several loops. When an electric current flows through the stator coils, it creates a magnetic field that interacts with the permanent magnets on the rotor, creating rotation.
Magnets:
Permanent magnets generate a fixed magnetic field. In FPV motors, they are attached to the inside of the motor bell with epoxy resin.
Motorglocke:
Die Motorglocke dient als Schutzgehäuse des Motors für die Magnete und Wicklungen. Einige Motorglocken bestehen im Allgemeinen aus leichten Metallen wie Aluminium und sind, wie Miniaturlüfter konstruiert, um mehr Luftstrom über die Motorwicklungen zu leiten und so für zusätzliche Kühlung zu sorgen, während sich der Motor dreht.
Motorwelle:
Die mit der Motorglocke verbundene Welle ist das Arbeitselement des Motors, dass das vom Motor erzeugte Drehmoment auf den Propeller überträgt.
Durch Erhöhen der Statorbreite oder -höhe erhöhen sich das Statorvolumen, die Grösse der Permanentmagnete sowie die elektromagnetischen Statorspulen. Dadurch wird das Gesamtdrehmoment des Motors erhöht, sodass er einen schwereren Propeller schneller drehen und mehr Schub erzeugen kann (auf Kosten einer höheren Stromaufnahme). Der Nachteil eines grösseren Stators besteht jedoch darin, dass er schwerer und weniger reaktionsschnell ist.