How KV Value Affects the Thrust and Efficiency of Underwater Thrusters

1. What is KV Value?

The KV value (RPM / Volt) represents the number of revolutions per minute (RPM) the motor will theoretically increase for each volt of electrical input under no load.

For example:

• 300KV motor:
  12V × 300 ≈ 3600 RPM

• 1000KV motor:
  12V × 1000 ≈ 12000 RPM

Note:
KV value is not power and does not directly equal thrust. It simply reflects the motor's speed characteristics.

2. The Relationship Between KV Value and Thrust

✅ Key Conclusion:
In underwater thruster applications, low KV motors are typically better for generating greater effective thrust.

In real-world applications, we find that most ROVs (Remotely Operated Vehicles) and underwater robots do not require extremely high RPMs. Instead, they need to continuously produce stable thrust at low RPMs. For this reason, our underwater thrusters are designed with low KV, brushless motors to perform well under high loads and long operational durations, rather than using typical hobby motors.

3. Why is Low KV More Suitable for Underwater Thrusters?

A common question from customers is, “Why does my high KV motor draw a lot of current but produce little thrust?” The reason is usually a mismatch between the KV value, propeller, and water resistance.

To avoid such issues, our underwater thrusters undergo comprehensive pre-shipment testing to match KV, voltage, and propeller size, so customers don’t have to deal with trial and error. For example, motors like the A4650 and A5080 are finely tuned to address this, saving customers considerable time.

4. How KV Value Affects Efficiency and Battery Life

Low KV = Higher System Efficiency
For systems that need to run for extended periods (such as underwater inspection or research ROVs), efficiency and heat management are more important than peak thrust. In these applications, we usually recommend a low KV motor with higher system voltage (such as 24V or 48V). This is a proven solution used in many engineering-grade underwater propulsion systems.

5. KV Value, Voltage, and ESC System Matching

It’s essential to consider the ESC (Electronic Speed Controller) current capacity and control method when choosing the KV value. In underwater systems, even with the right KV motor, an undersized ESC can lead to overcurrent or overheating issues.

In our complete thruster systems, the motor, ESC, and propeller are matched and tested as an integrated unit, rather than selling "bare parameters" separately.

6. Practical Application and Motor Selection Recommendations

✅ ROV / Underwater Drones
For these applications, we recommend low KV motors (100–400KV), as they pair best with larger diameter propellers for stable, controllable thrust.

If your project involves ROVs, scientific equipment, or underwater robots, focus on thrusters specifically designed for these uses rather than generic high-speed motors. For example, our A5060 motor is ideal for these applications, providing precise and stable thrust.

7. Conclusion

The KV value itself does not directly determine thrust. What truly determines performance is the matching of the entire underwater propulsion system. In underwater applications, a low KV motor paired with the right propeller and ESC often strikes the best balance between thrust, efficiency, and reliability.

If you're selecting a thruster, motor, or ESC for your underwater project, focus on application scenarios and system compatibility, rather than just comparing parameters.

For more detailed information, visit our motor product page:
Underwater Thruster Motors to explore technical details and recommended configurations.