Every so often, we run into a situation that confuses even experienced motor designers.
Two drone motors look nearly identical on paper. Same stator size. Similar winding configuration. Comparable KV rating. Yet once they hit the test stand, one consistently produces more thrust and feels noticeably more responsive when throttle is applied.
The difference isn’t always obvious.
We’ve seen customers spend days checking ESC settings, winding data, bearings, rotor balance, and even propeller combinations before eventually finding the real cause.
More than once, that cause turned out to be the magnets.
In one case, two motors that shared almost the same mechanical design were using different neodymium magnet grades. One rotor contained N48SH magnets, while the other used N38H. The difference in remanence was roughly 0.1 Tesla, and their high-temperature magnetic stability wasn’t even in the same category.
On paper, those numbers don’t seem dramatic.
Once installed inside a drone motor spinning at high speed, they become surprisingly noticeable.
Magnets don’t move. They don’t carry electrical current. They sit quietly inside the rotor bell doing what appears to be a passive job. Yet the magnetic field they generate is one of the main factors determining how much torque a motor can produce and how quickly it reacts when throttle input changes.
Understanding What Magnet Grades Actually Mean
Magnet grades often look confusing at first glance.
Names such as N38H, N42SH, N48UH, or N50EH contain two separate pieces of information.
The number refers to maximum energy product, measured in MGOe. Higher numbers generally indicate stronger magnetic performance. An N48 magnet can typically generate a significantly stronger magnetic field than an N38 magnet of the same size, often in the range of 15% to 20% stronger depending on the exact specification.
The letters indicate temperature resistance.
Standard N-grade magnets usually operate safely up to around 80°C. H-grade increases that limit to approximately 120°C. SH extends it to roughly 150°C. UH reaches around 180°C, while EH and AH grades move even higher.
One misconception we encounter fairly often is the idea that the highest number is automatically the best choice.
In reality, motor design rarely works that way.
Higher magnetic energy doesn’t always translate into better overall performance, and higher temperature grades often involve trade-offs in other magnetic properties. Selecting a magnet is usually a balancing act between field strength, thermal stability, mechanical reliability, and cost.
At Kzron, we manufacture a full range of sintered neodymium magnets from N35 through N52, covering temperature grades from standard N to EH. Common UAV motor configurations include arc magnets, block magnets, and ring magnets, with radial magnetization, multi-pole magnetization, and custom magnetization patterns available depending on the application.
Why Magnet Strength Changes Thrust Output
At its core, motor torque comes from the interaction between magnetic fields and electrical current.
Stronger magnetic fields allow the motor to generate greater torque using the same amount of current.
Comparing N38 and N48 provides a useful example. N48 magnets typically offer remanence values around 1.42 to 1.45 Tesla. N38 magnets usually fall between 1.24 and 1.27 Tesla.
That difference may only be around 0.18 Tesla, but inside a motor it can translate into a torque increase of roughly 12% to 15% under similar operating conditions.
On a thrust stand, that might be the difference between producing 500 grams of thrust and producing 570 grams.
There is an important limitation, though.
The stator core must be capable of handling the additional magnetic flux. Once the silicon steel reaches magnetic saturation, stronger magnets stop delivering meaningful gains. Instead, additional losses appear as heat.
This is why upgrading magnets without considering the stator often produces disappointing results.
We once worked with a customer interested in switching directly to N52 magnets to increase thrust. The existing stator design still relied on relatively ordinary silicon steel laminations. After reviewing the design, we suggested improving the stator material first. Otherwise, much of the additional magnetic capability would simply be wasted.
Because Kzron manufactures both magnets and stator cores, we frequently help customers evaluate the magnetic circuit as a complete system rather than focusing on a single component.
Why Magnet Choice Also Affects Throttle Response
Pilots often describe some motors as feeling more connected to the throttle.
Others feel softer, slower, or slightly delayed.
Part of that sensation comes directly from magnetic performance.
A stronger magnetic field creates a steeper torque response to current changes. When throttle input increases, torque rises more quickly. The result is a motor that feels more immediate and responsive.
This becomes particularly noticeable in FPV racing applications where rapid throttle transitions happen constantly.
There is another factor that receives less attention: intrinsic coercivity, often expressed as Hcj.
Coercivity measures a magnet’s resistance to demagnetization.
During aggressive acceleration, winding currents can become very large. Those currents generate magnetic fields that partially oppose the rotor magnets. If coercivity is insufficient, the magnet’s field can weaken temporarily or, in extreme cases, suffer gradual degradation over time.
The effect isn’t always dramatic.
Sometimes it simply feels like the motor lacks consistency during hard throttle punches. Pilots may describe it as feeling slightly soft or less predictable.
This is one reason many high-performance FPV motors use SH or UH grade magnets. The goal isn’t only surviving high operating temperatures. It’s also maintaining stable magnetic performance during repeated high-current events.
For many FPV motor projects, Kzron typically recommends N48SH or N50UH as a practical balance between magnetic strength and resistance to demagnetization.
What Happens When the Wrong Magnet Grade Is Used
We’ve seen several recurring issues during customer troubleshooting projects.
One of the most common is gradual thrust loss caused by thermal demagnetization.
An agricultural drone manufacturer once reported that newly installed motors performed well at the beginning of the season but gradually lost lifting capability after months of operation. Hover throttle increased. Payload performance dropped.
Inspection revealed localized demagnetization on the rotor magnets. Remanence measurements showed roughly an 8% reduction.
The motors were using N48H magnets rated for around 120°C operation. During summer field work, internal motor temperatures regularly exceeded 130°C.
The result was fairly predictable.
After upgrading to N42UH magnets with a temperature rating around 180°C, the problem essentially disappeared under the same operating conditions.
Another issue involves inconsistent acceleration performance between motors from the same production batch.
In one FPV application, some motors felt noticeably stronger than others despite using identical electronics and windings. Investigation showed uneven magnetic field strength across several rotor assemblies. Some magnets had inconsistent magnetization. Others were not positioned accurately within the rotor bell.
The problem wasn’t the motor design itself.
It was manufacturing consistency.
This is one reason Kzron pays close attention not only to magnet production but also to rotor housing machining accuracy. Strong magnets only deliver their intended performance when installed correctly.
Mechanical durability matters too.
At high rotational speeds, magnets experience significant centrifugal loading. Improper magnet selection, excessive thickness, inadequate retention methods, or brittle material combinations can eventually lead to cracking.
Once a magnet fractures inside the rotor, the outcome is rarely good.
For higher-speed motor designs, we often recommend combining suitable magnet grades with improved retention features, adhesive systems, or carbon fiber reinforcement depending on the operating environment.
Temperature Changes Everything
One mistake we occasionally see is evaluating magnets only at room temperature.
Drone motors don’t operate at room temperature.
A motor hovering lightly and a motor climbing aggressively at full throttle may experience very different thermal conditions within only a few seconds.
As temperature rises, magnetic performance naturally decreases.
Some of this loss is reversible. Once the magnet cools, performance returns to normal.
The real concern is irreversible demagnetization.
Once operating temperatures exceed the magnet’s thermal capability, part of the magnetic structure changes permanently. Cooling the motor afterward does not restore the lost performance.
For this reason, magnet selection should always begin with the highest expected operating temperature, not the average temperature.
A reasonable safety margin is usually at least 20°C to 30°C above the anticipated maximum motor temperature.
At Kzron, every magnet batch undergoes testing for key parameters including Br, Hcj, and maximum energy product to ensure actual performance matches the specified grade.
Magnet Installation Accuracy Matters More Than Many Realize
Even the best magnet won’t perform properly if it’s installed incorrectly.
Inside a rotor bell, magnet positioning directly influences magnetic circuit efficiency.
Angular placement affects how effectively magnetic fields interact with stator windings. Axial positioning changes the effective magnetic overlap area. Concentricity influences air-gap consistency, vibration levels, and acoustic behavior.
These requirements ultimately depend on machining accuracy.
The magnet slots inside a Motor Housing must be manufactured precisely. Position, depth, spacing, and angle all matter.
Kzron supplies both magnets and matching Motor Housing components, allowing dimensions to be controlled as a complete assembly. Magnet slot tolerances are typically maintained within ±0.02 mm, while angular positioning remains within ±0.5°.
That level of control helps ensure the magnetic system performs as intended once assembled.
A recent example involved a 3115 drone motor platform. The original design used N38SH magnets. The customer wanted approximately 10% more thrust without redesigning the entire motor.
After reviewing the available rotor space, we recommended upgrading to N48UH magnets, improving magnet slot precision, and increasing magnet thickness from 2.5 mm to 3.0 mm where space allowed.
Testing showed maximum thrust increasing from 5.8 kg to 6.5 kg, roughly a 12% improvement. Full-torque response time dropped from 35 milliseconds to 28 milliseconds.
Material cost increased slightly.
Performance gains were significant enough that the customer adopted the design for their next-generation UAV platform.
At the end of the day, magnets remain one of the most influential components inside a drone motor. A few characters in a magnet grade—N38SH, N48UH, N50EH—may look like simple part numbers, but those specifications directly influence thrust, efficiency, response speed, thermal stability, and long-term reliability.
And in many cases, the difference between an average motor and an exceptional one starts with the magnetic field hidden inside the rotor.
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