A brushless outrunner motor’s size has a significant impact on its torque, power output, speed, and efficiency, among other performance metrics. Choosing the right motor size for a specific application is essential for maximizing the motor’s potential and optimizing the performance of your system.

How Motor Sizes Are Defined

Outrunner brushless DC motors are typically categorized by two primary dimensions: the diameter and length of the stator. These are often indicated by a numerical code on the motor itself. A standard labeling format would be something like “2212” or “3536,” where:

• First Two Digits (e.g., 22, 35): Indicate the stator’s diameter in millimeters.
• Last Two Digits (e.g., 12, 36): Indicate in millimeters the stator’s length.

This simple classification allows users to easily identify the motor’s size and its intended performance characteristics. Larger numbers generally mean more torque and power but also a larger physical size and weight.

Key Factors Affected by Motor Size:

• Torque: Larger motors generally provide more torque due to the larger diameter, allowing for better leverage in the magnetic field interaction. This is beneficial for applications requiring heavy lifting or high load-carrying capacity.
• Speed: Smaller motors tend to have higher speeds (measured in RPM), but they produce less torque. These motors are suited for high-speed applications where torque is less critical.
• Power Output: A motor’s size directly affects its power output capacity. Larger motors can handle higher voltages and currents, resulting in greater power output, whereas smaller motors are typically limited in power capabilities.
• Heat Dissipation: Larger motors are better at dissipating heat due to their increased surface area, which allows for more efficient cooling during extended or high-power operation.

Motor Model	Diameter (mm)	Length (mm)	Shaft Diameter (mm)	Weight (g)	KV Rating(KV)	Application
BLDC-1806	18	06	2	35	2000-3000	Small drones, quadcopters, microplanes
BLDC-2830	28	30	3	65	1000-2200	Medium to large drones, electric planes, gliders
BLDC-3536	35	36	5	150	600-1200	Large electric planes, high-performance drones, electric bikes
BLDC-4250	42	50	5	220	600-1200	Big electric aircraft, ultra-efficient drones, and electric bicycles
BLDC-5055	50	55	6	330	200-500	Electric bikes, large industrial applications, heavy-lift drones
BLDC-6374	63	74	8	820	500	60
BLDC-80100	80	100	10	1250	1200	72

Common Brushless Outrunner Motor Sizes and Their Applications

Different sizes of brushless outrunner motors are designed for specific types of applications. We’ll examine some of the most popular motor sizes and their usual applications below.

1806 Brushless Outrunner Motor

• Size: 18 mm diameter, 6 mm length
• KV Rating: 2000-2300 KV
• Applications: Small drones, quadcopters, microplanes
• Characteristics: These motors are compact, lightweight, and designed for small-scale applications where weight and size are critical factors. They are frequently utilized in micro aerial vehicles (MAVs) and racing drones, where maneuverability is more crucial than power.

2204 / 2205 Brushless Outrunner Motors

• Size: 22 mm diameter, 4 mm or 5 mm length
• KV Rating: 2300-2500 KV
• Applications: FPV drones, RC planes
• Characteristics: Popular in FPV (First-Person View) drones and small RC planes, these motors offer a great balance between weight, size, and power output. The 2204 and 2205 motors are known for their responsiveness and high RPM, which are ideal for fast-paced flying.

2212 /2620 Brushless Outrunner Motor

• Size: 22 mm diameter, 12 mm length
• KV Rating: 900-1200 KV
• Applications: Medium-sized drones, camera gimbals, RC helicopters
• Characteristics: This size motor is often used in camera-carrying drones, like the DJI Phantom series because it provides a perfect balance between power and efficiency. These motors are capable of producing enough thrust for stable flight and are highly efficient, ensuring longer flight times.

2830 / 2826 Brushless Outrunner Motors

• Size: 28 mm diameter, 26 mm or 30 mm length
• KV Rating: 1000-2200KV
• Applications: Medium to large drones, electric planes, gliders
• Characteristics: These motors offer higher torque and are suitable for heavier drones and electric planes. With increased power output, they are often used in large quadcopters or even hexacopters that need to lift heavier payloads like cameras or sensors.

3536 / 4250 Brushless Outrunner Motors

• Size: 35/42 mm diameter, 36 mm or 50 mm length
• KV Rating: 600-1200 KV
• Applications: Large electric planes, high-performance drones, electric bikes
• Characteristics: Known for producing high torque and power, 3536 and 4250 motors are used in larger, more demanding applications. These motors are ideal for large electric planes or drones that require the ability to carry heavy payloads or fly for extended periods. In electric bikes, these motors provide strong, reliable propulsion.

5055 / 5065 Brushless Outrunner Motors

• Size: 50 mm diameter, 55 mm or 65 mm length
• KV Rating: 200-500 KV
• Applications: Electric bikes, large industrial applications, heavy-lift drones
• Characteristics: These larger motors are designed for applications requiring substantial amounts of torque. They are commonly used in electric bikes for propulsion, where the low KV rating provides high torque for climbing steep terrain. In drones, these motors are used for heavy-lift applications, such as carrying large cameras or equipment.

Choosing the Right Brushless Outrunner Motor Size

Selecting the appropriate motor size for your project requires understanding the specific needs of your application and balancing performance with practical considerations.

Step 1: Determine the Application’s Needs

Consider the type of application you are creating. Does your drone need to carry a camera? Is your electric bike designed for hilly terrain? Start by figuring out what your motor’s main objectives are in terms of torque, speed, and weight capacity.

Step 2: Determine Required Torque and Speed

Torque and speed are inversely related in brushless motors. If your project requires high torque (e.g., lifting a heavy load or driving a vehicle), you’ll need a larger motor with a lower KV rating. Conversely, for high-speed applications like racing drones, opt for smaller motors with higher KV ratings.

Step 3: Calculate Power Requirements

Understanding how much power your motor needs is crucial to avoid under-powering or overloading your system. Take into account the power supply’s voltage and the current your motor will require while it is under load. This will assist you in selecting the appropriate battery or power source for your project.

Step 4: Factor in Weight and Space Constraints

Compact and lightweight, smaller motors are perfect for applications where weight is an issue, such as remote control aircraft or drones. However, larger motors may be necessary if your project requires high torque or heavy lifting. Ensure that your motor fits within the available space and weight limits of your project.

Step 5: Ensure Proper Cooling

Consider the motor’s cooling capabilities, especially for high-power applications or extended use. Larger motors generally have better heat dissipation, but you may still need additional cooling systems (e.g., fans or heat sinks) in demanding environments.

In Conclusion

The versatility of brushless outrunner motors ensures that there is an appropriate motor size for nearly any requirement, providing high performance and long-lasting durability in both small and large applications.