Selecting the right brushless motor is a crucial decision when designing or upgrading a drone. The motor, which powers the propellers with mechanical energy converted from electrical energy, is the brains of your drone. Selecting the ideal brushless motor may have a big influence on your drone’s performance, efficiency, and overall flying experience.

Key Considerations for Choosing a Brushless Motor

Selecting the right brushless motor for your drone depends on several factors, each affecting the overall flight characteristics, such as speed, stability, and endurance. Let’s break down the most important considerations.

KV Rating: Understanding Motor Speed

The KV rating is one of the most critical specifications for any brushless motor. It refers to the motor’s RPM (rotations per minute) per volt applied. For instance, a motor receiving 1 volt will spin at 2300 RPM and have a KV rating of 2300 KV.

• High KV Motors: Motors with higher KV ratings (e.g., 2300 KV to 2700 KV) spin faster and are ideal for racing drones or FPV (First Person View) drones where speed and agility are prioritized. However, these motors tend to produce less torque, which can make them less efficient with larger propellers.
• Low KV Motors: Motors with lower KV ratings (e.g., 800 KV to 1400 KV) spin slower but produce more torque. They are more suitable for larger drones or aerial photography platforms that require stability and efficiency, especially when using larger propellers.

Motor Model	Diameter (mm)	Length (mm)	Shaft Diameter (mm)	Weight (g)	Power (W)	Voltage (V)
BLDC-2015	20	15	2	35	25	12
BLDC-2830	28	30	3	65	40	24
BLDC-3548	35	48	5	150	120	36
BLDC-4250	42	50	5	220	200	48
BLDC-5055	50	55	6	330	350	48
BLDC-6374	63	74	8	820	500	60
BLDC-80100	80	100	10	1250	1200	72

Motor Size and Weight

Brushless motors come in various sizes, typically represented by two numbers (e.g., 2205, 2306, 2812). The stator height in millimeters is represented by the second digit, and the stator diameter in millimeters by the first. A motor labeled “2205,” for example, has a stator that is 22 mm in diameter and 5 mm in height.

• Smaller Motors (e.g., 1806, 2204): These motors are lightweight and compact, making them ideal for smaller drones or micro quadcopters where weight is a primary concern. They are frequently utilized in high-speed maneuvering FPV racing drones.
• Larger Motors (e.g., 2212, 2814): Larger motors are heavier and provide more torque, which is essential for carrying heavier payloads, such as cameras or gimbals on aerial photography drones. These motors are also more efficient with larger propellers.

Thrust and Power Requirements

Thrust is the amount of force a motor generates to lift the drone into the air. It is a critical factor in determining how much weight your drone can carry and how quickly it can accelerate. Brushless motors typically have a thrust rating that indicates the maximum force they can generate when paired with specific propellers and voltage.

• Thrust-to-Weight Ratio: A 2:1 thrust-to-weight ratio is often a reasonable target. This means your drone’s motors should produce twice as much thrust as the total weight of the drone (including the frame, battery, and payload). For instance, you want the aggregate thrust of all motors to be 2 kg if your drone weighs 1 kg. This will ensure sufficient power for hovering, climbing, and maneuvering.
• Power Output: Measured in watts, it is calculated by multiplying voltage by current. To calculate the required motor power for your drone, you can use the following formula:

Power (W) = Voltage (V) x Current (A)

• Ensure that the motor you choose can handle the power requirements of your drone without overheating or drawing too much current from the battery.

Voltage and Battery Compatibility

The voltage supplied to the motor is another critical factor. Brushless motors are designed to work with specific voltage ranges, which are determined by the type of battery you’re using. Most drone batteries are LiPo (Lithium Polymer) and are available in various cell counts (e.g., 3S, 4S, 6S), where each cell supplies approximately 3.7 volts.

• 3S Batteries (11.1V): Typically used with smaller motors and drones that require less power. Higher KV motors are frequently used in conjunction with 3S batteries.
• 4S Batteries (14.8V) and 6S Batteries (22.2V): Used with more powerful motors for high-performance drones, such as racing or heavy-lift drones. Motors with lower KV ratings are typically paired with higher-voltage batteries to achieve the desired RPM without overheating.

Make sure your motor is compatible with your drone’s battery to avoid damaging the motor or other components.

Propeller Size and Motor Matching

The propeller is a crucial part of the motor setup, as it determines how effectively the motor can convert electrical energy into thrust. Propeller size and pitch must be matched to the motor’s KV rating and power output for optimal performance.

• Smaller Propellers (e.g., 4 to 5 inches): Smaller propellers are paired with high KV motors (e.g., 2300 KV or above) for high-speed flight, typically used in racing drones. They generate less thrust but allow for faster acceleration and higher maneuverability.
• Larger Propellers (e.g., 6 to 10 inches): Larger propellers are paired with low KV motors (e.g., 800 KV to 1400 KV) for stability and efficient flight, especially for carrying payloads. Greater power produced by larger propellers enables the drone to hover more effectively and carry greater loads.

Another factor is the propeller’s pitch, where a greater pitch results in more forward push at the expense of increased drag.

Matching the Motor to Other Drone Components

When selecting the right brushless motor, it’s essential to ensure compatibility with other critical drone components, such as the ESC, battery, and frame.

ESC (Electronic Speed Controller) Compatibility

The ESC is responsible for delivering the right amount of power to the motor. Each motor requires an ESC with an appropriate current rating. For example, if your motor draws a maximum of 20 amps under load, you should select an ESC rated for at least 25 amps to ensure safe and reliable operation.

In addition to the current rating, the ESC should also support the type of battery you’re using (3S, 4S, etc.) and be compatible with your drone’s flight controller.

To learn more about ESCs, you can read this article: Electronic Speed Controller (ESC) Troubleshooting

Battery Capacity and C-Rating

The amount of time your drone can fly is determined by the battery’s capacity, which is expressed in mAh (milliamp-hours). Larger motors generally consume more power, so they will require a higher-capacity battery to sustain longer flight times.

The C-rating of the battery is also important, as it indicates how quickly the battery can discharge power. Ensure that the battery can supply enough current to meet the motor’s demands without overheating.

Frame Size and Motor Mounting

The size of your drone’s frame will determine the maximum motor size and propeller diameter that can be used. Most drone frames have predefined motor mounting holes that are designed for specific motor sizes (e.g., 2204 or 2212). Make sure that the motor you choose is compatible with your frame’s mounting pattern and can accommodate the appropriate propeller size.

Typical Errors to Steer Clear of While Selecting a Brushless Motor

When selecting a brushless DC  motor for your drone, it’s easy to make mistakes that can lead to poor performance, overheating, or even damaging your drone. Here are some common mistakes to avoid:

• Selecting the Incorrect KV Rating: Higher KV motors aren’t necessarily the best choice. Choose a lower KV motor if you’re making a drone for aerial photography, as you’ll need stability and low RPM. On the other hand, if you’re building a racing drone, a high KV motor will give you the speed and responsiveness you need.
• Mismatching Motors and Propellers: Using propellers that are too large for your motor can cause excessive current draw, leading to overheating and reduced efficiency. Always check the manufacturer’s recommended propeller size for your motor.
• Ignoring Weight: Heavier motors may provide more torque, but they also add to the total weight of your drone, which can reduce flight time and maneuverability. Always balance motor power with the drone’s weight requirements.

Real-World Examples of Motor Selection

Racing Drone

• Motor Size: 2205 or 2306
• KV Rating: 2300-2700 KV
• Propeller Size: 5-inch
• Battery: 4S (14.8V)
• Use Case: High-speed, responsive motor for quick acceleration and sharp turns, ideal for racing and freestyle flying. A higher KV rating ensures fast RPM, while the 5-inch propeller provides the balance of speed and thrust for agility.

Aerial Photography Drone

• Motor Size: 2212 or 2812
• KV Rating: 900-1200 KV
• Propeller Size: 9-10 inch
• Battery: 4S or 6S (14.8V or 22.2V)
• Use Case: Stable motor with high torque for carrying a camera and providing smooth, steady flight. The low KV rating allows for slower, more stable flight, while larger propellers ensure enough thrust to lift the drone with a payload.

Long-Range Drone

• Motor Size: 2812 or 3510
• KV Rating: 700-1000 KV
• Propeller Size: 10-inch or larger
• Battery: 6S (22.2V)
• Use Case: Efficiency-focused motor for extended flight times and long-range missions. Low KV motor paired with larger propellers for high thrust and efficient power consumption.

In Conclusion

Choosing the right brushless DC motor for your drone requires balancing many factors. Not only should you consider the specific requirements of your drone (whether it is for racing, aerial photography, or remote missions), but you also need to consider choosing a high-quality brushless DC motor manufacturer to select a motor that will give you the best performance and efficiency to maximize your profits.