Why are two 2204 2300kv motors from different brands not the same?

We all know that kv defines how fast a motor spins in relation to the voltage, or RPM = kv * v. If so, why are two 2204 2300kv motors from different brands not the same? Why is a cobra 2204 2300kv diferent from an Emax 2204 2300kv and Sunnysky 2204 2300kv?

The reason lais in the RPM formula:

RPM = Kv * V

If we try comparing two 2204 2300kv motors using this RPM formula we will find that they are identical, since they are both marked as 2300kv. But, this formula does not describe the “whole story”. V refers to a voltage slightly different than your battery’s voltage.

This is what V really is:

V = Vbatt – Vloss

RPM = Kv * (Vbatt – Vloss)

Vbatt is your battery voltage (either 12.6v on 3s or 16.8v on 4s). Vloss is voltage “lost” because of “something” (we’ll get there).

This “something” wastes part of the energy sent to the motor and results in a slower RPM than the one we “anticipated” before this post 🙂

This wastful “something” is internal resistance – the motor’s internal resistance to be exact, or Rm.

Vloss = Rm * I

RPM = Kv * [Vbatt – (Rm*I)] 

If so, what is Rm?
This variable is listed by most manufacturers. Either by stating an internal resistance or a no load amperage.

These are a factor of how the coils are made. What are they made of, how thick the wire is, heat dissipation and more.

Using the no load amperage we can calculate the internal resistance of a motor:

Rm = Vbatt / Istall

In Summery,

The internal resistance of a motor has a negative effect on the motor speed. This effect is the reason why motor speeds vary from one brand to the other.


10 thoughts on “Why are two 2204 2300kv motors from different brands not the same?”

  1. Greetings! Very helpful advice in this particular article!
    It’s the little changes that will make the biggest changes.

    Thanks a lot for sharing!

  2. Wow! After all I got a web site from where
    I know how to genuinely get helpful information concerning my
    FPV miniquads

  3. This website was… how do you say it? Relevant!!

    Finally I have found something which helped me. Thanks a
    lot!

  4. Way cool! Some very valid points! I appreciate you writing this write-up and also the rest of the site is also really good.

Leave a Reply to quest bars Cancel reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.