A drone motor operates under changing loads during flight, from steady hovering to rapid climbing, sharp turns, and sudden acceleration. These changes affect motor speed, torque, and power losses, including copper loss and stator iron loss.

This article examines how stator iron loss contributes to motor efficiency and heating, using motor test results, thermal research, and electrical steel performance data.

Key Takeaways

Stator iron loss contributes to drone motor heating and efficiency, alongside copper and mechanical losses.
Higher absolute iron loss does not necessarily indicate lower efficiency, as demonstrated by recent drone motor research.
The thermal benefit of lower-loss NGOES depends on motor cooling conditions and the contribution of stator loss to total heating.

How Core Loss Fits into Drone Motor Efficiency

Motor efficiency measures the proportion of electrical input power converted into useful mechanical output at the shaft.

Motor Efficiency (%) = Mechanical Output Power / Electrical Input Power × 100

Mechanical output power depends on shaft torque and rotational speed. It should not be confused with complete propulsion system efficiency, which also involves the electronic speed controller (ESC), propeller, and other components.

Tyto Robotics explains in its guide to measuring brushless motor and propeller efficiency how voltage, current, torque, and RPM measurements are used to evaluate motor performance.

The difference between electrical input and mechanical output comes from several loss mechanisms.

Loss Type	Main Source	Effect on Motor Performance
Copper loss	Electrical resistance in motor windings	Generates heat as current flows through the windings
Stator iron loss	Changing magnetic flux in electrical steel	Consumes electrical energy and generates heat within the stator
Rotor electromagnetic loss	Losses in rotor magnetic and conductive components	Adds to electromagnetic losses, depending on motor design
Mechanical loss	Bearing friction and windage	Consumes mechanical power during rotation

For example, higher torque demand generally requires more winding current, increasing copper loss. Meanwhile, stator iron loss depends on magnetic excitation and material properties.

What Drone Motor Test Data Reveals About Efficiency and Losses

A 2026 study published in Actuators, Integrated Performance Prediction Method for Drone Propulsion BLDC Motor Considering Square Wave Current and Mechanical Losses, examined the performance of a 600 W-class outer-rotor BLDC motor for drone propulsion.

The following operating points were reported in the study:

Parameter	Operating Point 1	Operating Point 2
Rotational speed	2,571 rpm	5,460 rpm
Electrical input power	94.20 W	719.20 W
Mechanical output power	61.90 W	589.68 W
Motor efficiency	65.71%	81.99%
Stator iron loss (FEA)	2.38 W	11.62 W
Copper loss (calculated)	4.34 W	49.37 W
Estimated mechanical loss	25.12 W	66.05 W

Source: Park et al., Actuators, 2026. Input power, output power, and efficiency are experimental values; stator iron loss is obtained through FEA, copper loss is calculated, and mechanical loss is estimated through loss separation.

1793584002044-Drone Motor Efficiency and Iron Loss Comparison.webp

Comparison of drone motor efficiency and stator iron loss at 2,571 rpm and 5,460 rpm, based on published BLDC motor research.

At 5,460 rpm, calculated stator iron loss increased to 11.62 W, almost five times the value at 2,571 rpm. Nevertheless, measured motor efficiency rose from 65.71% to 81.99% because total losses accounted for a smaller share of input power.

Estimated mechanical loss exceeded stator iron loss at both operating points.

How Operating Conditions Change the Importance of Core Loss

Changes in motor speed and torque alter the relative contributions of copper, iron, and mechanical losses. At high-current operating points, winding losses can become particularly important.

A change in motor efficiency may affect electrical power demand at a particular shaft operating point. However, actual flight time also depends on propeller performance, aircraft weight, battery characteristics, and the broader propulsion system.

How Stator Core Loss Affects Motor Temperature

Stator iron loss originates from changing magnetic flux within the electrical steel. The dissipated energy becomes heat in the magnetic core.

That heat can move into surrounding components, including the stator structure, windings, and motor housing, before being transferred to the environment.

1793583992175-How Stator Core Loss Affects Motor Temperature.webp

Cutaway illustration of a drone BLDC motor showing heat generation from stator core loss and airflow cooling around the motor.

Heat Generation Is Not the Same as Temperature Rise

If a material change reduces stator iron loss by 5 W while other losses remain unchanged, the motor generates 5 W less heat. The resulting temperature reduction depends on thermal resistance, airflow, heat distribution, and operating duration.

During short periods of high power, heat is stored in motor components before temperatures reach a new equilibrium. During sustained operation, the balance between heat generation and dissipation becomes more important.

Heat produced in the electrical steel and heat produced in the windings may follow different thermal paths.

What UAV Motor Thermal Research Shows

A 2024 study published in Aerospace, Heat Transfer Models and Measurements of Brushless DC Motors for Small UASs, examined heat transfer in small outrunner BLDC motors.

The researchers conducted wind-tunnel experiments on four motor sizes under load and developed a heat-transfer correlation for these motor configurations.

A separate 2025 study published in IEEE Access, Thermal Analysis of Outer Rotor BLDC Motor for Drone Considering Airflow Ventilation Cooling, investigated how motor-generated airflow and ventilation affect the thermal behavior of a drone outer-rotor BLDC motor.

Neither study directly compared the thermal performance of different electrical steel grades.

When Lower-Loss NGOES Can Make a Difference

Non-oriented electrical steel is commonly used in laminated motor stators. Its core-loss and magnetic induction characteristics influence electromagnetic performance.

Evaluate the Potential Reduction in Total Motor Loss

Suppose a motor has an electrical input of 1,000 W and delivers 900 W of mechanical shaft power, giving it 90% efficiency.

If a material change reduces stator iron loss by 10 W, and mechanical output and all other losses remain unchanged, the electrical input would fall to 990 W.

The corresponding efficiency would become approximately 90.9%.

Parameter	Original Motor	Hypothetical Material Improvement
Mechanical output	900 W	900 W
Electrical input	1,000 W	990 W
Total motor loss	100 W	90 W
Motor efficiency	90.0%	90.9%

Illustrative calculation only. It assumes the same mechanical output and a 10 W reduction in stator iron loss without changes to other losses. It is not a measured HWHG product result.

Material Selection Still Depends on Magnetic Performance

Engineers may need to compare NGOES grades at appropriate frequencies and magnetic flux densities, particularly when the motor operates over a broad speed range.

Magnetic induction characteristics must also support the required electromagnetic design.

HWHG's Electrical Steel Core Loss vs Frequency explains how changing test conditions affects the interpretation of material core-loss data.

Thickness and downstream processing introduce further trade-offs, covered in the Electrical Steel Lamination Thickness guide.

How Manufacturers Can Verify Efficiency and Thermal Benefits

Evaluating a lower-loss electrical steel grade requires separating the material's contribution from changes caused by other motor components or test conditions.

1. Establish Comparable Operating Points

The motors should be evaluated at equivalent shaft speed and torque conditions, with consistent electrical supply and cooling arrangements wherever practical.

Measurements should cover operating points relevant to the intended application rather than only the maximum rated speed.

Input power and mechanical output can then be used to determine motor efficiency.

2. Estimate Individual Loss Components

Measured motor efficiency reveals total losses but does not directly identify how much loss occurs in the stator core.

Electromagnetic analysis can estimate stator iron loss using the motor geometry, magnetic material data, and relevant operating conditions.

Copper and mechanical losses must also be considered to develop a useful loss breakdown.

3. Measure Thermal Performance

Temperature testing should be conducted under controlled load, ambient, and airflow conditions.

Depending on the test setup, manufacturers may measure winding temperatures, stator temperatures, housing temperatures, or a combination of these.

Temperature measurements should be interpreted together with operating duration. A short test may reveal initial heating behavior without establishing steady-state temperature.

If two motors use different electrical steel grades, differences in cooling arrangements or other motor parameters can obscure the contribution of the material itself.

4. Check the Finished Stator

Cutting and punching can alter the magnetic behavior of electrical steel. As a result, the finished stator may not retain exactly the same loss characteristics measured on the original material.

Electrical Steel Support from HWHG

1790740647706-HWHG Electrical Steel Coils .webp

HWHG titanium coil and strip supplied with material certification and traceability records

HWHG manufactures and supplies non-oriented electrical steel coils, including thin-gauge options, for motor applications. Drone motor manufacturers can inquire about available grades, magnetic performance data, coil specifications, and coating requirements for their projects.

Conclusion

Lower-loss NGOES can reduce one source of heat generation in drone motors, but its practical benefit depends on the finished motor's operating and thermal conditions. Material comparisons should therefore focus on measurable changes in efficiency and temperature.

Drone Motor Efficiency: How Stator Core Loss Affects Heat and Performance

Outrunner vs Inrunner Drone Motors: Design, Torque, and Stator Differences

50,000 RPM EV Motors: What Ultra-High-Speed Designs Mean for Electrical Steel

Amorphous Metal vs NGOES for High-Speed EV Motors: Benefits, Limits, and Trade-Offs

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