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A Comprehensive Guide to Brushless Motor KV Ratings for Drones: How to Select the Right One to Balance Payload Capacity and Speed

When selecting drone motors, the KV value is paramount. However, discussing KV values without considering voltage levels (3S to 24S) amounts to mere theoretical speculation. The KV value (speed constant) defines the motor's fundamental characteristics, while voltage directly amplifies its rotational speed and thrust. Only by combining these factors can one precisely match different payload and speed requirements – from 3S RC aircraft to 24S large-scale logistics drones. Grasping this logic eliminates 90% of the trial-and-error involved in motor selection.

1. First, clarify: the core of selection lies in the combination of KV rating and voltage.

1. The Essential Definition of KV Values

The unit for the KV value is rpm/V(Revolutions per minute / Volts per minute), commonly understood as:No-load speed of the motor per minute at 1 volt input。

Core formula:Actual no-load speed = KV value × battery voltage

2. The Core Impact of Voltage Levels

Voltage and KV values are complementary partners:
  • High voltage (12S–24S): Compatible with medium-to-low voltage motors, utilising voltage to compensate for rotational speed while retaining high torque (suitable for heavy loads);
  • Low voltage (3S–6S): Requires pairing with medium-to-high KV motors to achieve the required rotational speed (suitable for light loads and compact units).
  • For the same KV value, higher voltage yields greater maximum rotational speed and thrust (though this must be matched with motor power and thermal management capabilities).

II. The Core Principle of KV Values: The ‘Inverse Balance’ Between Speed and Torque

The KV value is determined by the number of turns in the motor winding, directly influencing core performance, and this relationship is irreversible:

  • Low-KV motors: Featuring numerous winding turns, these motors deliver high torque and strong load-bearing capacity, making them suitable for high-voltage applications.
  • High-KV motors: Featuring fewer winding turns, these motors deliver rapid rotational speeds and responsive performance, making them well-suited for low-voltage applications.

III. Precise Matching of KV Value with Load Capacity and Speed

  • High KV: 3S–6S, suitable for mini aerial photography drones
  • Low KV: 12–24S, suitable for large agricultural drones and heavy-duty logistics drones

IV. Practical Steps for Selecting KV Values Under Voltage Conditions

  1. Define core requirementsDetermine whether the drone is designed for ‘speed priority’ (e.g., racing drones) or ‘payload priority’ (e.g., cargo drones), and establish the payload capacity range.
  2. Select voltage levelSelect the number of battery cells based on the machine's size and load capacity;
  3. Match KV values: Referring to the above description, narrow the KV range based on ‘voltage + load’;
  4. Verification of thrust redundancyEnsure the motor's single-axis thrust is ≥1.5 times the single-axis load. For example, a 60kg quadcopter distributed across four axes results in a single-axis load of 15kg; the motor's single-axis thrust must be ≥30kg.
  5. Verify motor parametersConfirm that the motor power and maximum current are compatible with the battery/ESC to prevent motor overheating at high voltages.

Summary

The KV value serves as the motor's “characteristic label”, while voltage acts as its “performance amplifier”. The core principle of selection lies in balancing rotational speed and torque through voltage adjustment: opt for “low voltage + high KV” for light-load, high-speed applications, and “high voltage + low KV” for heavy-load, stable operation.

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