Inrunner BLDC Motor vs Outrunner BLDC Motor: Which is Better?

When deciding between an outrunner bldc motor and an inrunner bldc motor for your accessory, we’ll provide the answer you need to consider.
The simple conclusion:

For speed, choose an internal rotor motor.

For torque, choose an external rotor motor.

What is a BLDC motor?

A BLDC motor consists of a motor (stator and rotor), a controller, and a position sensor. It lacks traditional brushes and a mechanical commutator. Compared to brushless motors, it offers high efficiency, long life, and low noise. This has led to its increasing application, particularly in the medical, industrial automation, and automotive industries.

Of course, BLDC motors also have some disadvantages, such as the requirement for an electronic controller, a relatively complex internal structure, and higher costs.

– BLDC Motor Structure and Material Selection

Inrunner BLDC Motor vs Outrunner BLDC Motor

Inrunner BLDC Motor

Structure:
Rotor: The permanent magnet rotor is located at the center of the motor.
Stator: The stator coils are wrapped around the rotor.

Operation:

When energized, the stator coils generate a rotating magnetic field that attracts or repels the permanent magnet rotor, causing it to rotate. The motor shaft is directly connected to the rotor, so the rotor drives the shaft.

Applications:
Drones, wind turbines, power tools

Outrunner BLDC Motor

Structural Features:
External Rotor: The permanent magnet rotor is a cup-shaped structure wrapped around the exterior.
Internal Stator: The stator coil is located in the center of the motor and is stationary.

Operation:

Current is applied to the stator coil to generate a rotating magnetic field, which drives the external permanent magnet “housing” to rotate. The motor shaft is fixed to the center of the stator inside, and the rotating housing directly drives the load.

Applications:
Blowers, ceiling fans, cooling fans, propeller motors

* Comparison of different parameters

Feature	Inrunner	Outrunner	Core Reason
Structure & Size	Slender and compact; small rotor moment of inertia	Short and thick (flat); large rotor moment of inertia	Differences in rotor position and diameter
Speed & KV Value	High rotational speed; typically has a high KV value	Low rotational speed; typically has a low KV value	Small rotor diameter leads to low linear speed, requiring higher rotation
Torque	Relatively low torque	High torque; high torque density	Outrunner structure provides a larger force arm
Heat Dissipation	Stator is external, with large heat dissipation area and good performance	Stator is internal; heat accumulation occurs, making heat dissipation a challenge	Different positions of the core heat-generating components
Weight & Efficiency	Usually lighter; high efficiency in high-speed ranges	May be heavier (due to outer magnetic housing); high efficiency in low-speed, high-torque ranges	Differences in design and application objectives
Typical Applications	RC models (speed boats, racing aircraft), CNC spindles, blowers	Drones, multi-rotors, RC aircraft, gimbals, direct-drive hubs	Determined by speed and torque characteristics

How to Choose？

High speed required – Choose Inrunner Motor.
Examples: Racing drones, high-speed vacuum cleaners, power tools.

High torque required at low speed – Outrunner Motor.
Examples: Drones, aerial photography aircraft, gimbal stabilization, hub motors for electric scooters.

Space constraints
Long, narrow spaces: Inrunner Motor is more suitable.
Flat, compact spaces: Outrunner Motor is more suitable.

Heat dissipation conditions
Good air/water cooling: Inrunner Motor has a clear advantage.
Enclosed spaces: Exercise caution when selecting Outrunner Motor and consider additional cooling measures.

FAQs

Q1: Does the Outrunner motor’s slow speed mean it performs poorly?
A1: No. It directly outputs high torque at a low speed, eliminating the need for a speed reduction mechanism in many applications, resulting in greater simplicity and efficiency.

Q2: Can I use an Inrunner motor as an Outrunner?
A2: Absolutely not! The structures are completely different; the fixed and rotating components are reversed.

Q3: Why are Outrunners so commonly used in high-end drones?
A3: Because they require the highest thrust-to-weight ratio and torque for maneuverability, and the Outrunner’s characteristics are a perfect match.

Q4: Which is more durable?
A4: Durability depends largely on build quality, bearings, and the operating environment. In theory, both can be very durable.