A Comprehensive Analysis of 7-Inch, 10-Inch, and 15-Inch Platforms

1. Introduction: The Paradigm Shift in FPV Propulsion

The trajectory of First Person View (FPV) drone technology has undergone a radical divergence over the last half-decade. What began as a discipline dominated by the standardized 5-inch freestyle quadcopter has splintered into specialized heavy-lift and long-range verticals. As operators demand the ability to carry cinema-grade payloads (such as the RED Komodo or Sony FX6) or traverse mountain ranges with multi-kilometer signal penetration, the propulsion requirements have scaled non-linearly. The physics governing a 30,000 RPM 5-inch propeller do not translate directly to a 6,000 RPM 15-inch propeller. This scaling introduces complex challenges regarding torque density, thermal management, magnetic saturation, and structural rigidity.

This report serves as a definitive technical resource for selecting Brushless Direct Current (BLDC) motors for large-frame multirotors, specifically focusing on the 7-inch, 10-inch, and 15-inch classes. It moves beyond superficial specification sheets to analyze the engineering philosophies of four dominant manufacturers—T-Motor, GEPRC, Emax, and MAD Components. By synthesizing empirical test data, material science (e.g., stator lamination thickness, magnet grades), and aerodynamic principles, this analysis establishes a robust methodology for propulsion system integration.

The transition from “miniquad” motors to “heavy-lift” actuators requires a fundamental understanding of the “Cube-Square Law” as it applies to drone performance. As the linear dimensions of the drone double, the area (disk loading) increases fourfold, and the volume (mass) increases eightfold. Consequently, the motor selection process is not merely about finding a “bigger” motor; it requires a complete architectural rethink regarding voltage sag, back-electromotive force (Back-EMF), and the mechanical impedance of the stator.

2. Fundamental Physics of Large-Scale BLDC Propulsion

To accurately select a motor for extended frames, one must first deconstruct the electromechanical environment in which these motors operate. The interplay between stator volume, KV rating, and propeller moment of inertia forms the “Iron Triangle” of propulsion efficiency.

2.1 Stator Volume Thermodynamics and Torque Density

The stator—the stationary component of the motor containing the copper windings and iron core—is the engine’s combustion chamber. Its volume determines two critical performance metrics: the maximum magnetic flux capacity (torque potential) and the thermal mass (heat dissipation capacity).

Stator volume V is calculated as a cylinder, ignoring the localized geometry of the stator teeth:

Where $r$ is the stator radius and $h$ is the stator height.

For a standard 5-inch freestyle drone, a stator volume of approximately 500-600 mm³ (typical of a 2207 or 2306 motor) provides sufficient torque to change the propeller’s RPM almost instantaneously. However, as the propeller diameter increases, the rotational inertia ( $I$ ) of the propeller scales with the square of the radius. To maintain control authority—specifically the ability to stop a spinning prop to arrest a flip or roll—the motor’s torque must scale aggressively.

Research indicates distinct volume thresholds for large-frame platforms:

7-Inch Class: Requires a stator volume between 900 mm³ and 1,100 mm³. This is typically satisfied by 2806.5 or 2807 stator sizes. Utilizing a smaller motor, such as a 2306, on a 7-inch prop results in magnetic saturation, where the iron core cannot carry any more magnetic flux, leading to heat spikes and a loss of control known as “washout.”
10-Inch Class: The volume requirement jumps to 2,000 mm³ to 2,500 mm³. This necessitates 3110 or 3115 class motors. The aerodynamic drag of a 10-inch blade is substantial, and insufficient stator volume results in sluggish response and dangerous oscillation during descent (prop wash).
15-Inch Class: These platforms, often categorized as X-Class or Industrial Heavy Lift, operate in volumes exceeding 5,000 mm³. Motors such as the 4214, 5215, or the T-Motor U-series (e.g., U8) are required to generate the Newton-meters of torque necessary to spin massive carbon fiber airfoils.

2.2 The KV Rating, Voltage, and Tip Speed Limits

The KV rating (RPM per Volt) represents the motor’s velocity constant. It is strictly tied to the Back-EMF generated by the spinning rotor. For large-frame drones, the selection of KV is constrained by the aerodynamic speed limit of the propeller tips.

Aerodynamic efficiency plummets and noise increases exponentially as propeller tips approach Mach 0.7. For a 5-inch prop, this allows for 30,000+ RPM. However, for a 15-inch prop, the rotational speed must be kept below roughly 6,000-7,000 RPM to remain efficient. This physical constraint dictates that as stator size increases, KV must decrease.

7-Inch: 1300KV – 1700KV.
10-Inch: 900KV – 1100KV.
15-Inch: 350KV – 500KV.

This reduction in KV is typically paired with an increase in system voltage (from 6S to 8S or 12S) to maintain total power output (Watts) while minimizing current (Amps). High voltage systems are inherently more efficient for heavy-lift applications because resistive losses are driven by current, not voltage.

2.3 Bearing Load and Shaft Integrity

As propeller size increases, gyroscopic precession forces exert immense side-loads on the motor bearings and shaft. A 15-inch propeller acts as a giant gyroscope; tilting the drone requires fighting this angular momentum. This stress concentrates on the motor shaft and bearings.

Shaft Composition: Premium motors (T-Motor, BrotherHobby) often utilize hollow titanium shafts to balance weight savings with high tensile strength. Budget options (Emax) typically use hardened steel, which is heavier but less prone to snapping under shear loads.
Bearing Size: While a 5-inch motor might use a 9x4x4mm bearing, 10-inch and 15-inch motors must step up to larger diameters (e.g., 11mm or 13mm bearings) or utilize angular contact bearings (common in MAD Components) to withstand axial thrust loads without pitting the races.

3. Comparative Brand Architecture and Engineering Philosophies

Before analyzing specific size classes, it is vital to characterize the engineering DNA of the four primary manufacturers. Each brand targets a specific segment of the price-performance-durability matrix, and understanding these biases is crucial for informed selection.

3.1 T-Motor: The Industrial Benchmark

T-Motor is widely recognized as the vanguard of high-performance and industrial UAV propulsion. Their product lines are bifurcated into the “F-Series” (FPV) and “U-Series” (UAV/Industrial).

Engineering Focus: T-Motor prioritizes efficiency and vibration reduction. They frequently employ curved N52H arc magnets which minimize the air gap between the stator and rotor, thereby increasing magnetic flux linkage.
Material Science: In their high-end U-series (e.g., U8 II), T-Motor utilizes silver windings instead of copper. Silver has lower electrical resistance than copper, improving efficiency by up to 15% and reducing operating temperatures.
Reliability: The U-series motors often carry IP (Ingress Protection) ratings (e.g., IP55), featuring centrifugal cooling fans and weather-sealed bearings, making them the default choice for commercial operations where equipment failure is not an option.
Market Position: Premium pricing for professional and high-budget enthusiast applications.

3.2 Emax: The Value-Durability Nexus

Emax occupies the high-value segment, focusing on robustness and accessibility. Their “ECO” series disrupted the market by offering competent performance at a fraction of the cost of premium brands.

Engineering Focus: Emax motors, particularly the ECO II series, are designed for durability. They often feature thicker bells and steel shafts that can survive the high-impact crashes common in freestyle flying.
Trade-offs: To achieve their price point, Emax may use slightly lower grade magnets (e.g., N52SH or N48SH) or standard copper windings compared to the exotic materials found in T-Motor’s flagship lines. They are generally heavier than their competitors, which increases disk loading but adds structural resilience.
Market Position: The preferred choice for budget-conscious builds, educational fleets, and freestyle pilots who anticipate frequent hardware replacement.

3.3 GEPRC: The Integrated Modernist

GEPRC has transitioned from a frame manufacturer to a comprehensive ecosystem provider. Their motors (SpeedX2, EM series) are designed to integrate seamlessly with their popular long-range and cinematic frames.

Engineering Focus: GEPRC emphasizes weight reduction and cooling. Their “unibell” designs are often heavily machined to remove excess material, maximizing airflow over the stator windings.
Aesthetics and Design: Their motors often feature 7075-T6 aviation aluminum and unique anodizing finishes. They prioritize “smoothness” and linear throttle response, which is critical for the cinematic footage their “CineLog” and “Crocodile” drones are known for.
Market Position: Mid-to-high tier, targeting the dedicated long-range and cinematic FPV pilot who values a cohesive build aesthetic and weight optimization.

3.4 MAD Components: The Heavy-Lift Specialist

MAD Components distinguishes itself by focusing heavily on the “X-Class” and industrial sectors, often competing directly with T-Motor’s industrial lines but with a more aggressive focus on torque and extreme conditions.

Engineering Focus: MAD divides its line into “BSC” (Basic), “IPE” (Industry Pro Edition), and “X-Class” racing series. The IPE series is notable for its robust waterproofing and dustproofing (IP35/IP55), achieved through specialized bearing seals and coating technologies.
Technological Distinctiveness: MAD motors often feature “centrifugal fan” designs integrated into the rotor cap to actively force air through the windings during hover—a critical feature for heavy-lift drones that may remain stationary for long periods.
Market Position: A strong contender for X8 Cinelifters and heavy industrial rigs, offering a slightly more cost-effective alternative to T-Motor’s U-series while maintaining industrial specs.

4. The 7-Inch Class: Long-Range and Mountain Surfing

The 7-inch drone is the workhorse of long-range FPV. It must balance the agility required to pull out of a dive down a mountain face with the efficiency to cruise for 15-20 minutes.

4.1 Stator Geometry: The 2806.5 vs. 2807 Debate

The 7-inch market has standardized around two stator sizes: 2806.5 and 2807. While visually similar, their performance characteristics diverge noticeably.

2806.5 (Wide & Flat): This geometry maximizes the surface area of the stator relative to its volume, improving heat dissipation. The wider diameter provides a longer torque arm, increasing mechanical leverage. This size is favored for “cruisers” where smooth efficiency is paramount.
2807 (Tall & Voluminous): The increased stator height provides greater copper volume, leading to higher magnetic flux and raw torque. This size is preferred for “heavy” 7-inch builds (e.g., carrying a full GoPro Hero 11 rather than a stripped “Naked” GoPro) or for pilots who fly aggressively.

4.2 Detailed Brand Comparisons for 7-Inch

The following analysis integrates specific test data and user experiences.

T-Motor F90 (2806.5 – 1300KV)

The F90 is the reference standard for 7-inch propulsion.

Performance: In testing, the F90 (1300KV) demonstrates exceptional efficiency at cruise throttle (30-40%), making it ideal for maximizing flight times on 6S Li-Ion packs.
Dynamics: It is characterized by a very smooth, linear throttle curve. However, some pilots report that on extremely heavy builds (>1.2kg), it may lack the immediate “snap” of a 2807 when recovering from rapid descents.
Recommendation: Best for lightweight long-range builds focused on endurance.

Emax ECO II 2807 (1300KV)

The ECO II 2807 is a powerhouse that trades weight for torque.

Performance: The larger 2807 stator volume delivers noticeably higher torque than the 2806.5 class. This makes the drone feel more “locked in” in turbulent wind conditions.
Drawbacks: It is heavier than the F90 and GEPRC SpeedX2 equivalents. This added weight at the end of the arms increases the drone’s moment of inertia, potentially requiring higher P-term gains in the PID controller to stabilize.
Recommendation: Best for heavy freestyle 7-inch builds or budget-conscious pilots requiring robust durability.

GEPRC SpeedX2 2806.5 (1350KV)

Performance: The SpeedX2 splits the difference, offering a slightly higher KV (1350 vs 1300) for a higher top speed. Its unibell design is specifically optimized for cooling, addressing the heat soak issues common in long-range flights.
Recommendation: Ideal for cinematic pilots using GEPRC frames (like the Crocodile 7) who value a balance of speed and smooth video capture.

MAD Components BSC2807 (1500KV)

Performance: MAD enters with a higher KV option (1500KV). While 1300KV is standard for 6S, the 1500KV option is aggressive, suited for pilots who want higher top speeds or are flying at high altitudes where the air is thinner and props need to spin faster to generate equivalent lift.
Recommendation: High-altitude mountain surfing or aggressive 7-inch freestyle.

4.3 7-Inch Selection Matrix

Model	Stator Size	KV (6S)	Weight Class	Primary Characteristic	Optimal Use Case
T-Motor F90	2806.5	1300	Light	High Efficiency	Long-Range Endurance
Emax ECO II	2807	1300	Heavy	High Torque / Value	Heavy Freestyle / Budget
GEPRC SpeedX2	2806.5	1350	Medium	Cooling / Linear	Cinematic Video
MAD BSC2807	2807	1500	Medium	High RPM Power	High Altitude / Aggressive

5. The 10-Inch Class: Cinelifters and Heavy Payload

The 10-inch class has seen a resurgence driven by the “Cinelifter” movement—drones designed to carry cinema cameras with the agility of an FPV quad. The physics here are unforgiving; a 10-inch prop has massive surface area, and managing its drag requires substantial stator volume.

5.1 The “Washout” Phenomenon and Stator Sizing

A critical failure mode in 10-inch drones is “washout,” where the drone tumbles out of a sharp turn because the motors lack the torque to overcome the propeller’s inertia and aerodynamic drag. To prevent this, the industry has moved away from 28xx motors for 10-inch props, standardizing instead on the 31xx class (3110, 3115).

5.2 Voltage Architecture: The Move to 8S

While 6S (25.2V) is common, the 10-inch class is increasingly adopting 8S (33.6V) architectures. By increasing voltage, pilots can drop the KV (to ~900KV) and achieve the same RPM with lower current draw ( $P=VI$ ). This reduces heat in the ESCs and windings, which is critical when lifting 3kg+ payloads.

5.3 Detailed Brand Comparisons for 10-Inch

BrotherHobby Tornado T5 / Avenger 3115 (900KV)

BrotherHobby is a dominant force in the Cinelifter market.

Performance: The 3115 stator provides immense torque authority. The 900KV winding is perfectly tuned for 10-inch props on 6S-8S.
Reliability: These motors use high-grade Japanese NMB bearings, which are essential for supporting the large radial loads of 10-inch props. They are the “safe bet” for professional film sets.

Emax ECO II 3115 (900KV)

Emax has democratized heavy-lift propulsion with the ECO II 3115.

Value Proposition: Offering a 3115 stator at a budget price point allows for accessible heavy-lift projects.
Tech Specs: Features N52SH magnets (High Temperature rated) and a reinforced axle. While potentially less refined in balancing than the BrotherHobby, the raw torque output is comparable, making it an excellent choice for non-commercial heavy lifters.

GEPRC EM3115 and EM3110

GEPRC offers granularity in this class with two distinct sizes.

EM3110 (900KV): A lighter option (87.5g). This is suitable for “light” 10-inch builds (e.g., long-range cruising with a GoPro rather than a cinema camera). It saves weight but sacrifices peak torque.
EM3115 (900KV): The heavy hitter (115g), designed to compete directly with BrotherHobby. It supports up to 1620W of power, designed for the rigorous demands of carrying a RED Komodo.

MAD Components BSC3115 / X8 Applications

MAD explicitly markets their 3115 motors for X8 Coaxial configurations.

Coaxial Optimization: In an X8 setup (motors mounted top and bottom), the bottom motor operates in the “dirty” turbulent air of the top prop. MAD’s high-torque design helps maintain RPM stability in this turbulence, smoothing out the flight characteristics—a critical trait for cinema applications.

5.4 10-Inch Selection Matrix

Payload Tier	Recommended Motor	Stator Size	Battery Voltage	Rationale
Light (<1.5kg)	GEPRC EM3110	3110	6S	Weight savings extend flight time for LR cruising.
Cinema (>2.0kg)	BrotherHobby 3115	3115	6S/8S	Proven reliability; industry standard for Cinelifters.
Cinema (Budget)	Emax ECO II 3115	3115	6S	High torque at a lower price point; good for entry-level lifters.
Heavy X8 Coaxial	MAD BSC3115	3115	8S	Optimized for turbulent airflow in coaxial setups.

6. The 15-Inch Class: Industrial Lift vs. X-Class Racing

The 15-inch category represents a bifurcation in drone utility. Motors here are split into two distinct lineages: high-speed “X-Class” racing motors and high-efficiency “Industrial” motors.

6.1 X-Class Racing: Speed and Agility

These machines are essentially scaled-up racing drones. They require motors that can change RPM rapidly to execute rolls and loops.

BrotherHobby Tornado T10 (5215): The 5215 stator is a massive puck of torque.
- KV Ratings: 330KV – 500KV. Running these on 12S creates a terrifyingly powerful machine.
- Construction: Heavy-duty 7075 aluminum bells and hollow shafts are mandatory to survive the G-forces of freestyle maneuvers with 15-inch arms.
MAD Components XC Series (XC5500):
- Thrust: The “Crimson” series can generate over 6 kg of thrust per motor. A quadcopter with four of these produces 24kg of thrust, allowing a 5kg drone to accelerate with 5G of force. This is pure performance engineering.

6.2 Industrial Heavy Lift: Efficiency and Reliability

These drones fly autonomously for mapping, delivery, or agriculture. Agility is secondary to reliability and efficiency (g/W).

T-Motor U8 II KV85 / KV100: The U-Series is the gold standard for this application.
- Silver Windings: The U8 II utilizes silver windings to reduce internal resistance. This allows for efficiency ratings that can exceed 10-12 g/W at hover, significantly extending flight times compared to copper-wound hobby motors.
- Environmental Protection: Rated IP55, these motors are sealed against dust and water jets, allowing operation in light rain or dusty agricultural environments—a feature absent in the X-Class racing motors.
- Cooling: The “U” design incorporates centrifugal fans that actively pull air through the stator core, keeping temperatures low even during static hovering.
MAD Components M10 IPE:
- Industrial Pro Edition: MAD’s answer to the U8. It offers IP35 protection and is designed for heavy-lift endurance.
- Paramotor Roots: Derived from electric paramotor technology, the M10 IPE is built for sustained high-load output without thermal throttling.
GEPRC EM4218 (350KV):
- The Hybrid: GEPRC offers the EM4218 as a bridge. It is an industrial-capable motor (13-15 inch props) but priced closer to the hobbyist market. It lacks the IP ratings of the T-Motor U-series but offers massive power (1800W) for heavy-lift camera rigs.

6.3 15-Inch Selection Matrix

Application	Motor Model	Stator / Spec	KV (12S)	Key Feature
X-Class Racing	BrotherHobby T10	5215	500KV	Extreme Torque for Freestyle
X-Class Racing	MAD XC5500	5500	505KV	Max Thrust (6kg+)
Industrial / Ag	T-Motor U8 II	8729	85-100KV	IP55, Silver Windings, Efficiency
Heavy Cinema	GEPRC EM4218	4218	350KV	High Power Budget Heavy Lift

7. How to Choose the Best Motor: A Methodology

Selecting the correct motor is a calculated process, not a brand preference. Follow this step-by-step methodology to determine the optimal stator and KV for your specific build.

Step 1: Define Total All-Up Weight (AUW) and Target TWR

You must estimate the total weight of the drone, including the battery and payload.

Hover Thrust: The motors must generate thrust equal to the AUW at ~30-40% throttle to hover efficiently.
Thrust-to-Weight Ratio (TWR):
- Aerial Photography / Mapping: Target 2:1 to 3:1. (e.g., 5kg drone needs 10-15kg max thrust).
- Long Range FPV: Target 4:1.
- Freestyle / X-Class: Target 6:1 to 8:1.

Step 2: Determine Propeller Size Constraints

Frame Limit: What is the maximum prop size your frame supports?
Physics Check:
- 7-Inch: Standard for 1-2km range + mild freestyle.
- 10-Inch: Required for payloads >1.5kg (Cinema cameras).
- 15-Inch: Required for payloads >3kg or flight times >30 mins.

Step 3: Select Voltage (S-Count)

Higher voltage allows for lower current (Amps) for the same power (Watts).

7-Inch: 6S (25.2V) is the modern standard. 4S is obsolete for performance builds.
10-Inch: 6S is minimum; 8S (33.6V) is recommended for heavy cinelifters to keep ESC temps down.
15-Inch: 12S (50.4V) is mandatory for X-Class and heavy industrial lift to prevent melting connectors.

Step 4: Match Stator Volume to Prop Size

Refer to the “Iron Triangle” rules established in Section 2:

7″ Prop: ~1,000 mm³ Volume (2806.5 / 2807).
10″ Prop: ~2,200 mm³ Volume (3110 / 3115).
15″ Prop: >5,000 mm³ Volume (4214 / 5215 / U8).

Step 5: Verify ESC Compatibility

The motor’s “Max Continuous Current” must not exceed the ESC’s rating.

Safety Margin: Always apply a 20% safety margin.
- Example: A BrotherHobby 3115 motor pulls 55A burst. You need an ESC rated for at least $55A \times 1.2 = 66A$ . Therefore, choose a 60A-65A ESC (typically 4-in-1 for 7/10 inch, individual ESCs for 15 inch).

8. Conclusion

The landscape of large-frame FPV propulsion is defined by a trade-off between efficiency and authority.

For the 7-inch long-range pilot, the T-Motor F90 (2806.5) remains the efficiency king, while the Emax ECO II 2807 offers a high-torque, durable alternative for aggressive flying.
For the 10-inch Cinelifter, the BrotherHobby 3115 and GEPRC EM3115 provide the critical torque density required to stabilize heavy cinema cameras, with 8S voltage becoming the preferred architecture to manage thermal loads.
For 15-inch Industrial applications, the T-Motor U8 II stands alone with its silver windings and IP55 rating for mission-critical reliability, while the MAD XC series and BrotherHobby T10 unlock the adrenaline-fueled world of X-Class giant drone racing.

Success in these large classes is not achieved by simply buying the most expensive motor; it is achieved by respecting the physics of disk loading and stator saturation. Match the stator volume to the propeller inertia, align the KV with the voltage for optimal tip speeds, and the result will be a platform that performs with the precision of a scalpel, regardless of its size.