FPV Drone Motors: A Comprehensive Guide to Selection

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Welcome to the world of FPV drone motors! This extensive guide will provide a detailed exploration of motor construction, design features, and the elements that impact motor performance and efficiency. Gaining an in-depth understanding of these design choices empowers you to make the perfect motor selection for your upcoming drone project.

Differentiating Between Brushless and Brushed Motors:

In the realm of remote-controlled devices, two main motor types coexist: brushless and brushed. For FPV drones, the choice is clear — brushless motors take the lead due to their superior blend of durability and power. While brushed motors find their place in toy drones for their cost-effectiveness, this guide focuses exclusively on brushless motors, the primary choice for most FPV drone enthusiasts.

Estimating Drone Weight and Frame Size:

A critical initial step is estimating the total weight of your FPV drone, accounting for all components, from the frame and flight controller to ESCs, motors, propellers, receivers, video transmitters, antennas, LiPo batteries, cameras such as GoPros, and more. Although pinpoint accuracy isn’t obligatory, providing a close estimate is imperative. It’s often better to err on the side of overestimation to ensure your drone has ample power for takeoff rather than struggling due to underpowering.

Simultaneously, establishing the frame size is vital because it dictates the maximum allowable propeller size for your drone.

Determining Thrust Requirements:

To calculate the minimum thrust your motor and propeller combination should deliver, you need to know the estimated total weight of your drone. A rule of thumb suggests that the combined maximum thrust from all motors should be at least double the total weight of your quadcopter. Inadequate thrust can result in sluggish control response and difficulties during takeoff.

For example, if your drone weighs 1 kg, the combined thrust generated by all motors at 100% throttle should be at least 2 kg, with each motor producing 500g of thrust in the case of a quadcopter. Having more thrust available than needed is advantageous.

Racing drones necessitate significantly higher thrust-to-weight ratios, sometimes reaching 10:1 or even 14:1. In contrast, acro and freestyle flying typically require a minimum 5:1 thrust-to-weight ratio. A higher ratio offers greater agility and acceleration but can be challenging to control, especially for beginners.

Even in the realm of slower and more stable aerial photography drones, aiming for a thrust-to-weight ratio exceeding 3:1 or even 4:1 is recommended. This not only improves control but also allows for extra payload capacity.

Connecting a Brushless Motor:

To operate a brushless motor, you need an Electronic Speed Controller (ESC). Unlike brushed motors, which have only two wires, brushless motors feature three wires that can be connected to the ESC in any order. Reversing the rotation direction is as simple as swapping any two of the three wires.

Demystifying Motor Size: Brushless RC motors are typically labeled with a four-digit number format AABB:

“AA” signifies the stator width (or stator diameter). “BB” represents the stator height, both measured in millimeters.

The stator is the stationary part of the motor, housing wire coils. These coils are coated with enamel to prevent short-circuits as they are wound into multiple loops. When an electrical current flows through the stator coils, a magnetic field is generated, interacting with the permanent magnets on the rotor to drive motor rotation.

Exploring the Motor’s Key Components:

Motor Stator: The motor stator constitutes the stationary part of the motor and consists of multiple metal coils. These coils are coated with enamel to prevent short-circuits as they are wound into multiple loops. The flow of electrical current through the stator coils generates a magnetic field that interacts with the permanent magnets on the rotor, resulting in rotational motion.

Magnets:

Permanent magnets are responsible for creating a fixed magnetic field within FPV motors. These magnets are affixed to the interior of the motor bell using epoxy.

Motor Bell:

The motor bell serves as a protective casing for the motor’s magnets and windings. Typically constructed from lightweight metals such as aluminum, certain motor bells feature designs resembling miniature fans. These designs facilitate additional airflow over the motor windings, aiding in cooling during operation.

Motor Shaft:

The motor shaft, connected to the motor bell, is the functional component of the motor responsible for transmitting the torque generated by the motor to the propeller.

Enhancing Motor Size:

Increasing either the stator’s width or height results in a larger stator volume, larger permanent magnets, and expanded electromagnetic stator coils. Consequently, this enhances the motor’s overall torque, enabling it to rotate heavier propellers at faster rates and produce greater thrust. However, there is a trade-off as a larger stator also means increased weight and reduced responsiveness.

Understanding the Role of KV:

KV is an abbreviation representing the number of revolutions per minute (RPM) a motor completes when subjected to 1 volt (1V) without any load, such as a propeller. For example, a 2300KV motor powered by a 3S LiPo battery (12.6V) will spin at approximately 28,980 RPM without a propeller (2300 x 12.6). Typically, motor manufacturers provide a rough estimation of the KV rating.

When a propeller is attached to the motor, the RPM decreases significantly due to air resistance. Higher KV motors will strive to spin the propeller faster