How to Choose FPV Drone Motors

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This tutorial explains the basics of FPV drone motors: construction, design features and other factors that affect the performance and efficiency of a motor. Understanding the design decisions involved will help you choose the optimal motor for your next drone build.

Can’t decide which motor to get? Check out my FPV Drone motor recommendations.

Where to Start?

If you are new, make sure to check out our beginner’s guide to mini quad and FPV first.

Before choosing motors, you should at least have a rough idea of the size and weight of the drone you want to build. I will explain the process of determining motor size based on drone size, but if you are just building a 5″ FPV drone, you can jump straight to the “Motor Size” section.

Some of the most important considerations are:

• Motor weight
• Power (thrust)
• Efficiency (g/watt)
• Torque and response (RPM changes)

Brushless vs. Brushed Motors

There are two types of motors used in RC, Brushless and Brushed motors. Generally we use brushless motors on larger models (such as racing drones, and any bigger models), and Brushed on the micro drones and toy drones. We will focus on brushless motors in this guide.

Knowing the Total Weight and Frame Size

The total weight of the quadcopter should include all the components: frame, FC, ESC, motors, propellers, RX, VTX, antenna, ESC’s, LiPo battery, GoPro, and so on.

It doesn’t have to be 100% accurate, an estimation would be fine. It’s better to overestimate the weight and have extra power than underestimate, and struggle to take off. Adding 10-20 grams to compensate for the electrical wires, buzzer, zip ties etc is also a good idea.

By knowing the frame size, you can determine the maximum propeller size allowed. Further Reading: how to choose propellers for mini quad.

Calculating Thrust Required

With the estimated total weight of the craft, you can work out the minimum amount of thrust required for the motor and propeller combination to produce.

A general rule is that the maximum thrust produced by all motors is at least double of the total weight of the quadcopter. If the thrust is too little, the copter will not respond well to your control, it might even struggle to lift off.

For example if we have a quadcopter that weighs 1Kg, the total thrust generated by the motors at 100% throttle should be at least 2Kg, or 500g per motor (for a quadcopter). Of course it’s always nice to have more thrust available than needed…

For faster flying such as drone racing, you should expect the thrust to weight ratio (or power to weight ratio) to be much higher than the example above. It’s not uncommon to see 10:1, or even 13:1 thrust to weight ratios. Generally speaking, for acro flying, I recommend to have at least 5:1.

With a higher thrust to weight ratio, a quadcopter will have greater agility and acceleration, but it might become harder to control as well. Just a little touch of throttle will be enough to “shoot the quad into orbit like a rocket” :D Of course this depends on piloting skill too.

Even if you only just planned to fly a slow and stable aerial photography rig, you should aim at somewhere between 3:1 and 4:1 ratios. This does not only give you better control, but also provides room for extra payload in the future.

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Connecting Brushless Motor

You need an ESC (electronic speed controller) to drive a brushless motor. Unlike brushed motors which only have two wires, there are three wires in a brushless motor, and you can connect these wires to the ESC in any order. Simply swapping two of the three wires will reverse the rotation direction. It’s also possible to reverse motor direction in software.

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Motor Size Explained

The size of brushless motors in RC is normally indicated by a 4-digit number – AABB. “AA” is the stator width (or stator diameter) while “BB” is the stator height, both are measured in millimeter.

What is brushless motor stator? – A stator is the stationary part of the motor, this has ‘poles’, which are wrapped around by copper wires (windings). The ‘poles’ are made of many layers of thin metal plate that is laminated together with a very thin insulation layer in between.

• Motor stator: This is the stationary component of the motor that is made up of multiple metal coils. The coil wire is coated in an enamel that protects it from shorting to itself as it is wound in circles over and over again. When an electrical current is passed through the stator coils, it creates a magnetic field that interacts with the permanent magnets on the rotor to produce rotation.
• Magnets: The permanent magnets generate a fixed magnetic field. In an FPV motor, they are glued to the inside of the motor bell with epoxy.
• The motor bell is the case of a motor that protects the magnets and windings. It is generally made out of a lightweight metal like aluminium. Some motors bells are designed like miniature fans to direct more air flow over the motor windings as the motor spins for additional cooling.
• The shaft of the motor is attached to the motor bell. It is the working component of the motor that transfers the torque generated by the motor to the propeller.

When increasing the stator height, it increases the permanent magnet size more than the coil size, while increasing the stator width, it increases the electromagnetic coil size more than the permanent magnet.

Increasing either the width or height of the motor stator will increase the stator volume, as well as the size of the permanent magnets and electromagnetic stator coils. This will result in higher overall torque of the motor – it’s able to spin a heavier prop faster, and produce more thrust (but draws more current). The downside of bigger stator is it’s heavier, and also less responsive.

Taller Stator vs. Wider Stator

A wider motor has larger inertia when spinning. The mass of the motor is further away from the rotational axis, therefore it takes more energy to change RPM. For this reason, wider and shorter motors are generally less responsive than narrower and taller motors even if they have the same stator volume and generate the same amount of torque. A wider and shorter motor also means the magnets on the motor bell are smaller, which hinders the power of the motor.

However, the advantage of a wider motor is better cooling thanks to the larger surface area on the top and bottom. Temperature is crucial to a motor’s performance. As the motor heats up, its ability to generate magnetic flux decreases which impacts efficiency and the ability to produce torque.

It might be oversimplified, but the width and height of a motor stator are basically a balance between responsiveness and cooling, the decision comes down to the type of flying you do. For example, for a relatively slow cinewhoop carrying a heavy camera, because the motors are constantly working hard, you might want to consider motors with a wider stator for better cooling. For fast and snappy racing/freestyle drones where responsiveness is crucial, taller stators are preferred.

A wider stator also allows for a larger bearing to be fitted. Larger bearings are better for efficiency, smoothness and longevity.

Bigger stator is not always better. For example, 2207 motors are more than capable of handing typical 5″ propellers, by using the much heavier 2506 motors of the same KV is most likely not going to provide any benefits since they’d have the same thrust, or even worse responsiveness. If you want to get more performance it’s perhaps better to go higher KV since it doesn’t add any weight. The 2506 motor would probably work better for 6″ props than 2207 though as the bigger prop requires higher torque.

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Motor Torque

A high torque motor allows for more rapid change of RPM and faster response time, you will get less prop wash oscillation and it will give you that instant and snappy response.

The torque of a motor are determined by many factors, for example:

• Stator size (volume)
• Materials: the type of magnets, quality of the copper windings
• Motor construction: such as air gap, number of poles and so on

But since motors in the FPV industry are manufactured in pretty similar specifications and design in recent years, stator size is the easiest way to quantify the torque of a motor.

Stator size can be calculated the same as the volume of a cylinder:

volume = pi * radius^2 * height

For example, for a 2207 motor, the stator volume would be

pi x (22/2)^2 x 7 = 2660.93

The bigger the stator volume, the more torque a motor can generate.

Now let’s take a look at a 2306 motor, the volume would be 2492.85, which means a 2207 motor has more torque than a 2306.

So when choosing a motor, what you want to do is to compare their motor stator volume, as well as the motor weight. A lighter motor with the same volume would be preferred, assuming other factors are equal.

So why don’t we just pick the biggest motor available? The answer is weight. Motors with bigger stator volume are also heavier, so it really depends on the application.

For example, for a light weight drone, it doesn’t need that much throttle to stay in the air, this gives them more left-over torque. Paired with lighter pitch propellers, the motors can spin them with less torque. So the motor torque requirement is low in this case, and you can probably get away with lighter/smaller motors which also keeps all up weight down.

The only time you don’t want a motor that is too powerful (too much torque) is that you prioritize “smoothness” over responsiveness. That’s because high torque motors are capable of changing RPM so fast, they can actually feel jerky and less smooth sometimes. It also creates more voltage spikes and electrical noise to the power system, that could affect gyro performance and overall flight performance if noise filtering isn’t optimal in your drone, contributing to oscillations.

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KV

“KV” is how many revolutions per minute (rpm) that a motor turns when 1V (one volt) is applied with no load (e.g. propeller) attached to that motor. Here is a more academic explanation of KV. For example, when powering a 2300KV motor with a 3S LiPo battery (12.6V), it will spin at around 28980 RPM without propellers mounted (2300 x 12.6). Typically KV is just a rough estimation specified by the motor manufacturer.

Once a propeller is mounted on the motor, the RPM will decrease drastically due to air resistance. Higher KV motors would attempt to spin the propeller faster, produce more thrust and power (while drawing more current). That’s why we tend to see larger props paired with low KV motors, while smaller and lighter props are better suited for high KV motors.

The KV of a motor can be determined by the number of copper wire windings in the stator. Generally, the higher number of turns of winding decreases the KV of the motor, while lower number of turns increases the KV. The magnetic strength of the magnets can also affect the KV value, stronger magnets will increase KV.

By pairing a high KV motor with an excessively large propeller, the motor will attempt to spin fast like it would with a smaller prop, but this will require more torque. As it tries to produce the required torque it will draw more current and subsequently generate too much heat. This will eventually lead to overheating and it can burn out the motor – when the motor overheats, the coating on the coil will start melting and causing electrical shorts inside the motor.

That’s why a higher KV motor is likely to run hotter than a lower KV one of the same motor size.

KV actually has an effect on the current and voltage limits of the motor too. As explained, higher KV motors have shorter windings and thus lower resistance. It lowers maximum voltage rating and increases the current draw for the motor and propeller combo. Anyway, when you buy a motor, it should specify what voltage you are allowed to use, and what the maximum current it can take on the product page.

There is a “Motor Output” limit in Betaflight that allows you to reduce the motor signal and use higher voltage batteries, e.g. you could fly 4S motors on 6S battery.  This might be a work around but it’s more likely to blow your ESC with high KV motors. The way the MOSFET in ESC works is by switching on and off, so the output voltage is always either the battery voltage or 0V. By limiting the motor output you are just setting a limit to how long you keep the MOSFET switched on, but you are still exposing the same higher voltage to the motor, and it’s more likely to cause issue than a lower KV motor that is rated properly to that higher voltage. It’s recommended to get the right KV motors for the battery voltage you plan to use.

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KV vs. Torque Constant

While motor KV does not have a direct effect on torque, it does to torque constant. The torque constant of a motor defines how much current it costs to create torque. KV doesn’t affect how much torque can actually be created. There are factors like magnet strength, air-gap, coil resistance that have a much more significant impact on torque production.

Higher KV motors have higher torque constant, which means they require more current to generate the same amount of torque compared to a lower KV motor. In order to generate the same amount of torque, the higher KV motor would require more current, results in extra losses in the ESC, battery and wires. Even worse, there would be more heat building up in the motor due to the higher current, making it harder to generate magnetic flux. Overall the higher KV motor is less efficient if you were to fly at the same speed as the lower KV motor.

Therefore it’s wise not to go crazy on KV, try to keep it moderate. It’s especially important if you are building a long range drone that prioritizes on efficiency and flight time.

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Mounting Holes

Common mounting patterns (hole distance) for 22xx, 23xx, 24xx motors are 16x19mm and 16x16mm. Modern 5″ racing 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 3mm arms, I use 5mm screws; for 4mm  arms, I use 6mm screws.

 

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Poles and Magnets

You might have seen specification such as “12N14P” printed on the box of a motor. The number before the letter N means the number of electromagnets in the stator, i.e. poles, and the number before P means the number of permanent magnets in the bell.

Different sizes motors have different number of poles, 22XX and 23XX motors generally have 12 poles and 14 magnets.

The number of poles determines the spacing between the poles if you have fewer poles, you can fill in more iron content in the stator, so you get more power out of the motor. But with a higher number of poles, the magnetic field is spreading out more evenly, and therefore you have a smoother running motor because you have a more fine controlled over the rotation of the bell.

• More poles = Smoother
• Fewer poles = More powerful

The pole configuration has to be a multiple of 3 because it’s a 3-phase motor and there are 3 wires into the motor, therefore the pole numbers have to be 9, 12, 15, 18 etc. That’s why the pole number is not easily changed, and thus it’s not an essential piece of information when picking motors especially for mini quad.

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Motor Windings

The number of copper windings or ‘turns’ on a stator pole determines the maximum current a motor will draw, while the thickness of the wire determines how much current the motor can handle before overheating.

Fewer turns = less resistance = higher KV. The downside is a reduced electromagnetic field on the stator and thus lower torque.

The opposite happens when we have more turns in the coil. The increase of copper produces a larger magnetic field on the stator pole and generates more torque. But due to the longer wires and higher resistance, the KV of the motor decreases.

To tackle these issues when increasing the power of mini quad motors, manufacturers choose to increase the number of windings while using thicker copper wires.

This will effectively reduce the resistance in the winding, and improve the power without sacrificing efficiency and torque. The motor would also be able to handle high current without burning out with larger wire gauge.

However thicker wires and more windings means a heavier motor, and the winding takes up more physical space so it requires a larger stator. That’s why we are seeing more bigger and heavier motors, and that’s also why bigger motors are generally more powerful.

Multi-Stranded vs. Single Stranded Windings

Single stranded windings are thicker, therefore manage heat better and better suited for those who run higher voltages like 5S or 6S. But you cannot pack as many wires around the stator because the gaps are larger between the thicker wires.

Multi stranded windings use 3 smaller wires to replace the 1 thicker wire in single stranded windings. Due to the thinner wires, they don’t carry as much heat and they will break easier physically.

But generally multi-stranded windings provide better performance than single stranded windings because you can pack the wires more tightly around the stator thanks to the smaller gaps between wires, and this will give you stronger magnetic field and a more powerful and efficient motor.

Note that the neatness of winding is also important, not only aesthetically, but also electrically. If the winding is messy and has a lot of wire crossings, the wires doesn’t cross the stator perpendicularly and the resulted magnetic field will be less efficient.

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Bearing

Motor bearing isn’t talked about a lot because there isn’t much info available, but I thought I should give you a basic introduction anyway.

The size of the bearing is not the outer diameter or the inner diameter, but the difference between the outer and inner diameter. The wider it is the larger the marbles/balls it can fit inside it. Larger balls can take more abuse to break, hold up better to a crash. But smaller balls are more stable and smoother at high speed/RPM.

There are motors marketed as using “Ceramic Bearings” – they use ceramic balls instead of steel balls, and they are indeed smoother, but easier to break.

The diameter of the hole in the bearing (inner diameter) also determines how big a shaft you can use.

9mm x 4mm is the good balance for durability and smoothness.

Popular bearings used in FPV drone motors are Japanese NSK, NMB, EZO etc. While the EZO bearings are hyped up to be the best, it’s difficult to measure how much better it really is to others. Not to mention you don’t know if the manufacturer is using the genuine thing, or just cheap clones.

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How to Decide on Drone Motor Size?

You can find out the component sizes to use in this order: Frame Size => Prop Size => Motor Size

By knowing the frame size, we can estimate what motor size we should use. Frame size limits props size, and each prop size requires a different motor RPM to generate thrust efficiently, this is where motor KV comes in.

You also have to make sure that the motors produce enough torque to spin your choice of propeller, this is where your stator size comes into play. Generally bigger stator size and higher KV means more current draw.

This table below is a general guideline, it’s not a hard-set rule, you might also see people using slightly higher or lower KV motors than this table suggests. Anyway it’s a good starting point.

It assumes you are powering the quad with 4S LiPo batteries, and frame size is referring to the wheelbase (aka diagonal motor to motor distance).

For a more detail table for different prop size and Lipo voltages, check here.

Frame Size	Prop Size	Motor Size	KV
150mm or smaller	3″ or smaller	1105 -1306 or smaller	3000KV and higher
180mm	4″	1806, 2204	2600KV – 3000KV
210mm	5″	2205-2208, 2305-2306	2300KV-2600KV
250mm	6″	2206-2208, 2306	2000KV-2300KV
350mm	7″	2506-2508	1200KV-1600KV
450mm	8″, 9″, 10″ or larger	26XX and larger	1200KV and lower

Voltage and Current Draw

It’s important to understand that voltage has a large impact on your motor and propeller choice. Your motor will try to spin faster with a higher voltage, thus draw a higher current. Ensure you are aware of how much thrust your motors produce and how much current they will draw.

When you know the current draw of the the motor and prop combination, you are now ready to choose ESC for your drone.

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Basic Measurements of Motor Performance

Once you have decided on motor size, you probably still have many options available to choose from. To pick the best motor for your application, you can consider the following factors:

• Thrust
• Efficiency and Current Draw
• Weight

The decision here really depends on your application, flying style, and how you want your aircraft to perform.

Thrust

Thrust is probably the first thing people look at when choosing a motor.

Higher thrust gives you faster acceleration, but you also need to be aware of current draw and efficiency. Don’t abuse your batteries with an amperage-hungry motor/prop combo.

If your quad draws a lot of current at high throttle, the maximum discharge rate of your battery has to be able to keep up. The battery must also have a large enough capacity to ensure acceptable flight time.

While thrust is an important aspect in selecting a motor, it’s not the only thing to consider.

Motor Weight

The weight of a motor often gets overlooked, which can be a very important factor for acrobatics and racing drones.

Since the motors are mounted at the four corners of the frame, they have a strong influence on the responsiveness of your quad. Heavier motors increase the angular moment of inertia of your quad, the motors must work harder and requires more torque (not just thrust) in order to change attitude.

In practice, when your quad is doing flips and rolls, it takes time to pick up angular acceleration, move to the desired position and stop. Heavier motors will take longer to pick up that angular speed, and also longer to slow down. That’s why it feels less responsive. If your flying involves more fast changing in direction (e.g. freestyle and racing), motor weight matters more than just cruising in straight line (cinematic cruisers).

Efficiency and Current Draw

Motor efficiency is typically calculated by dividing thrust by power at 100% throttle, measured in grams per watt (g/w). The higher this number is, the more efficient the motor.

It’s important to look at efficiency through the whole throttle range, not just the top end. Some motors might be efficient at lower throttle, but could lose efficiency by drawing increasingly higher current as they approach their limits.

Another good way to look at efficiency is to use “grams per amp” (thrust/current).

Generally, the more thrust generated, the larger the current drawn to produce that thrust, so motors with high thrust and low current are preferred. Inefficient motors either generate too little thrust or draw too much current.

Every motor responds differently to different propellers, carefully choosing your propeller is the key to balance thrust and efficiency.

Efficiency and current draw affect your choice of battery. An efficient motor with large current draw might abuse your battery and cause voltage sags.

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Advanced Motors Performance Factors

Many quadcopter motor properties are not mentioned by the manufacturers and can only be found through more technical testing.

• Torque
• Response Time
• Temperature
• Vibration and balance

Motor Torque

Torque is the force that turns the propeller, it determines how fast a motor can increase and decrease RPM. In other words, how easy it is for the motor to move the mass of the rotor, prop, and most importantly, the air.

Torque greatly affects the performance of your quad, specifically, how precise and responsive it feels in flight. A motor with high torque gives more snappy response, because of the faster change of RPM. You might even experience less prop wash with more torque.

High torque also means you can run heavier props (at the cost of drawing more current). If a low torque motor is driving a propeller that is too heavy for it (aka over-prop), the motor will be unable to produce enough force to spin it at the desired RPM, resulting in poor efficiency and overheating.

One drawback of high torque motors though, is oscillation. Motors with high torque are able to change RPM so rapidly that it can actually amplify error (in PID loop), causing oscillation that can be hard to eliminate even with PID tuning, especially on the yaw axis.

Torque is directly affected by stator size, bigger stator size = more torque. Other factors that can increase torque are:

• Stronger magnets
• Minimizing the air gap between permanent magnets and stator, such as using arc magnets
• Thinner stator laminations

Another benefit of high torque is higher tolerance to propeller weight (thus runs better with a wider range of props). But you should benefit from using lighter props as RPM changes quicker.

Response Time

Motor Response Time is also dependent on torque, high torque motors often have faster response time. One easy way to measure response time is to see how long it takes for a motor to reach maximum RPM from 0.

Response time will be affected largely by the weight and pitch of your propeller choice. Remember that atmospheric conditions can have an effect too. At low altitude, for example, the air is thicker, this means that there is a greater number of air molecules that the propeller must physically move, to produce thrust. At high altitude, your props will spin faster and react quicker to changes in throttle, but the overall thrust will be reduced, because there are fewer air molecules for the prop to interact with.

Temperature

Temperature affects brushless motors because the magnets used in our motors have a weaker magnetic field when operating at high temperature, they also demagnetize faster at the motor gets too hot which affects lifespan.

Over-propping your motors and using full throttle excessively, will cause your motors to run hot. This will degrade the performance of the motor and the magnets over time, therefore motor designs which aid cooling often equates to a longer lifespan. That is of course, provided you don’t destroy it in a crash beforehand!

Vibration

Vibration caused by the motors can have a number of unpleasant side effects to the performance of your quad.

If a motor has poor balance or build quality, you might experience vibration that can affect your PID controller. As the frequency of the vibration changes at different throttle levels, this can make your quad very difficult to tune.

A motor suffering from vibration will also produce a greater amount of electrical noise than one which is running smoothly. This electrical noise can affect your Gyro sensor, making flight performance even worse, and it will also degrade your FPV video quality if you are powering your FPV system from the same battery as the motors and ESC’s.

Many have successfully soft mounted motors, and the flight controller to reduce vibration, with some really positive results.

Remember that damaged, bent and unbalanced propellers can also cause problematic vibrations.

Features in FPV Drone Motors

There are so many variables that affect the performance of a motor, it can get very controversial and complicated. For example, motors with the same stator size and KV, you can have very different thrust, current draw and response time even using the same prop. Differences in the design and material both have a great impact on performance.

Here I will explain a few different motor design features that contributes to better performance, which can also change the characteristics of the motor.

Motor Shaft

To mount a propeller, you put the hole in the centre through the motor shaft. Most brushless motors for 3″, 4″, 5″ and 6″ propellers have M5 shafts (5mm diameter).

The construction of motor shaft is changing over time. It used to be a solid aluminium rod, later manufacturers start using hollow shaft with titanium. Similar weight but much stiffer and harder to bend. However drilling the hole in the middle of the titanium shaft increases the cost of manufacturing significantly.

And more recently they’ve come up with a new motor shaft design, by inserting a steel rod in the hollow shaft for the extra strength.

Magnet Type

Magnets used in brushless motors are graded according to their magnetic field strength, such as N50, N52, N54 etc. The higher the number, the stronger the magnetic field. For example, N52SH will be better than N50SH.

A stronger magnetic field is theoretically capable of generating power more efficiently, providing more torque and a faster motor response time.

When you turn a motor by hand, you can feel the notches, the stronger you can feel them is actually a bad thing because it tells you how strong the magnetic force is, and how weak it is in between magnets, which tells you the magnetic field is not even. Weaker notches usually means a smoother motor.

Magnets will lose magnetic strength when they reach certain temperature, therefore N52H is used to prevent this problem. The letter at the end has to do with operating temperature. It’s said that N52SH can withstand even higher temperature, but there is no data at the moment to indicate how much better N52SH is compared to N52H and N52.

It’s possible that magnets get loose in crashes or due to vibration. You can glue it back in the bell using Loctit 438.

Arc Magnets

Using arc magnets (aka curved magnets), is a technique to bring the magnets closer to the stator; allows for a smaller and more consistent air gap (We will explain what air gap is later).

In fact, the way a permanent magnetic field works means that with a curved magnet, the strongest magnetic point of each pole is no longer on the surface of the magnet, as it is with standard (non arc) magnets.

The ‘epicentre’ of the field of the pole on the outside of the curve, will be below the surface of the magnet, and the epicentre of the pole on the inner curve will actually be above the surface. In this manner, the magnetic fields of the permanent and electromagnets are actually brought even closer together, over and above the physical reduction of the air gap.

Apart from the shape, some manufacturers test mini quad motors with different thicknesses of magnet, often finding that a slightly thinner magnet (therefore a weaker magnetic field) can actually provide better results.

Air Gap

“Air gap” in a motor refers to the distance between the permanent magnets and the stator. Magnetic force degrades non-linearly with distance, so reducing the gap between the two significantly boosts the power of the motor.

A smaller air gap not only makes the motor more powerful, it also improves torque and response. The downside of tighter airgap is the increase in current draw and decrease in efficiency. Also there is concern regarding durability, if the motor bell takes any sort of impact and it gets out of alignment and shifted at all, the magnet can run into the stator and end up getting shattered.

Stator Laminations

A lamination is the thickness of the individual sheets of metal stacked up in the motor stator, thinner lamination allows you to stack more layers of stator plates for the same height of the motor stator.

In a nutshell, the thinner stator lamination, the better. Laminations help to reduce a phenomenon known as Eddy Current, which generate heat in a changing magnetic environment. Thinner laminiations means less power is wasted on generating the eddy currents (leads to undesired magnetic field) and making motors more powerful and efficient.

C-Clip / Shaft Screw

To hold the motor bell to the base, motor manufacturers use one of these methods on the bottom of the motor to lock the shaft in place: C-clip, E-clip or a screw. Each of these ways has their pros and cons, and it’s hard to say which one is the best.

Generally speaking, screws are better for user maintenance as it’s easier to remove a screw than a C-clip or E-clip. But screws suffer from risk of over-tightening and locking the shaft (making the motor harder to spin).

There are reports about C-clips popping off during flight, which resulting the motor bell flying off and causing a crash. However, be aware that screws are also not immune to this problem.

Aluminium Alloy

The metal used for the motor bell and motor base determines the durability of the motor. There are two common types of aluminium alloy used in FPV motors: 7075 and 6082. The number designates the different series of aluminium alloy grades and chemical composition.

In a nutshell, 6082 has more ductility and is more formable while 7075 is more rigid and hold up better against crashes. 6082 is used back in the days before 2016/2017, but 7075 is the most common in modern motors and is thought to be stronger against impact.

Unibell

Unibell (unibody top bell) is a preferred moto bell design, which is in one piece of metal instead of separate pieces of metal glued together. The main benefit of unibell is better durability, but it costs more to manufacture. Non-unibell could split into pieces in a hard crash and it’s irreparable and the damaged motor or bell needs replacing in most cases.

Bottom Design

In motor base design, there is the more traditional “closed bottom” approach, and the more recent “naked bottom” style. There are pros and cons to both of these designs.

The “closed bottom” design means a stronger base, however the “naked bottom” tend to be lighter by removing the excess material, the weight saving is around 2g.

Closed base motors are less likely to get dirt trapped inside the bell, against the argument that, naked bottom are easier to clean the dirt out.

With naked bottom, you can see clearly how far the screws are going in, and you have less chance of shorting the motor winding if the screws are too long. (This happens often to beginners with closed bottom motors.)

However, the closed bottom provides better strain relief to the wires in case of crashing and stretching.

Flux Ring Design

A flux ring is the round steel ring inside the bell that contains the magnets. The bell is usually made of aluminium, 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 the torque.

PoPo Technology

The “Pop on Pop off” system is basically a motor shaft with spring loaded bearing for installing and removing props quickly. For a more detail overview and product list check out this article.

Other Features

• Soldering tabs
• 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 integrating ESC inside the motor. Personally I think solder tabs on the motor can come in handy, it allows you to use a lighter gauge wire to save weight on less amp hungry applications. They should also be easily repairable if the wires get pulled off, which can often spell the end of a motor of typical design.

CW and CCW Drone Motors

You will rarely see brushless motors labelled as CW (clockwise) and CCW (counter clockwise).

This does not indicate the direction the motor spins. Brushless motors can spin either direction. This label differentiates the direction that the motor bolt is threaded. This is done so that as the motor spins, the torque from the propeller pushes  the motor nut to tighten rather than loosen. This keeps your props from loosening and coming off while you fly. This means you will need two of each for your 4 motor layout in standard Betaflight rotation.

• Front Left: CW
• Front Right: CCW
• Back Left: CCW
• Back Right: CW

To tell if you have the correct threaded motor on, simply hold the prop nut on the shaft, then start turning the motor with your hand in the direction it should spin. If the nut tightens then you have the correct one :)

Personally I prefer to have the same threads on all my motors, so I don’t confuse myself with the different prop nuts. If you have to replace a prop nut at the hardware store, it can be a real headache trying to find a CCW threaded nuts  (or more commonly in the hardware jargon, a ‘left hand thread nut’). Prop nuts these days are lock nuts (have rubber inside), they stay on relatively well when tightened down and doesn’t get loose easily.

Balancing FPV Drone Motors

When you receive your motors, the first thing to do is balance them. Although it’s not always necessary, it’s a good practice. I personally only do this on large motors though such as 2212 or bigger.

I find balancing unnecessary for many brand name mini quad motors because the quality is generally good enough. However with cheaper options that are becoming available don’t be surprised to find less attention paid to quality control.

Edit History

• Oct 2013 – Article created
• Nov 2016 – Updated with new facts
• May 2017 – Added “Motor Features”
• Jan 2018 – Corrected some grammar mistakes
• Mar 2018 – Added info about “windings”, “poles”, “bearing” and “Torque”
• Oct 2018 – Added info about mounting pattern, PoPo technology
• Oct 2019 – Updated connection to ESC
• Apr 2022 – Added info about Unibell