Motors and ratings

Brushless Motor Ratings and Specifications

Kv Rating

• Kv refers to the RPM of the motor per volt "without a load".
• Example: A motor with a Kv rating of 3,500kV will spin 3,500 RPM for every volt applied.
• On a 2S LiPo battery, a 3,500kV motor will spin around 25,900 RPM.
• On a 3S LiPo battery, the same motor will spin around 38,850 RPM.

Motor Turn Rating

• The "turns" of a motor refers to the amount of wire windings around each of the motor’s rotor poles.
• Lower turns equal higher top end speed and lower torque/acceleration.
• Higher turns equal lower top end speed but higher torque/acceleration.

Current Rating / Amps

• Max current rating is the maximum amount of current a motor can handle safely, measured in Amps.
• Continuous current rating is the Amps a motor can handle safely over a long period of time.
• Factors affecting current draw: Kv rating, voltage of batteries, weight of Drone, and prop size.

Watts and Horse Power

• Watts are the power rating or the horsepower equivalent of a Brushless Motor.
• 746 Watts equals one Horse Power.
• Watts = Amps multiplied by battery voltage (Amps x Volts).
• Motor efficiency is around 80 – 90%, so some wattage is turned into heat.

Motor Heat Management

Problem

• Heat is the enemy of the setup and can damage components over time.
• Example: A motor producing 180W with 85% efficiency will generate 27W of heat.

Solution

• Use a heat sink and motor fan to reduce heat.
• Other options: change gearing or prop size, use a more efficient motor, reduce voltage or amps.

Motor and ESC Compatibility

Overview

• Motor and ESC must be compatible in terms of maximum input voltage.
• Exceeding the recommended voltage can damage the setup.

Parts

• Motors: U8 Pro KV135
• Recommended prop: G29x9
• Batteries: 6S LiPo

Steps

1. Ensure the motor and ESC are compatible with the battery voltage. 2. Calculate the top RPMs based on the motor Kv rating and battery voltage. 3. Choose a motor that balances speed and efficiency based on the specific goal.

Notes

• A balanced motor Kv rating provides the best of both worlds.
• Higher Kv motors produce more heat and handle less voltage.
• Lower Kv motors are more efficient and can handle more voltage.

Motor Heat and Efficiency

Summary

• Motor heat is a critical factor affecting performance and longevity.
• Efficient motors cost more but reduce heat generation.

Key Points

• Heat sink and fan are effective for managing motor heat.
• Motor efficiency is typically 80 – 90%, with the rest converted to heat.
• Heat management is crucial for maintaining motor performance and lifespan.