Motor KV Guide – 6S Hype?

Guest Article
This post is from my guest author Felix Niessen (interview with Felix) from FETtec and will shed light on the current trend of increasing motor KV numbers in connection with the „6S Hype“.

The current motors KV trends (rounds per minute per volt) go to ever higher values. People think you „cant loose something“ if you never go full throttle.

That is not correct!

Of course you have a bit more power with a high KV motors at full throttle, but it is less efficient at lower throttle levels. Therefore, you should consider how much full throttle you really need, because the lower the average throttle is, the higher the current losses in the ESC and the motor cables are.

Losses occur in electrical conductors by the amount of the current (ampere), not the voltage (volts). The transported power (Watt) results from both values ​​(Volt × Ampere).

  •   2 volts × 10 amps = 20 watts
  • 10 volst ×   2 amps = 20 watts

You can reduces losses by replacing current (A) with voltage (V).

For example:

Setup 1 and Setup 2 are examples of 4S setups. Setup 1 with an efficient KV value and Setup 2 with a very high KV value.
In this example, the same power (rpm) is on the motor, the throttle has been adjusted to the motor KV value.

Setup 3 and Setup 4 are examples of 6S setups in a similar ratio to Setup 1 and Setup 2, with the same performance and rpm achieved.

Obviously in both examples the current (ampere) is higher at the higher KV value, at the same power. The ESC is used as the transformer and makes voltage (V) to current (A) in the required ratio. How strong this transformation is, depends on the desired rpm (the throttle signal), because motors with higher KV value run at higher rpm with a lower throttle signal (lower voltage (V)).

Due to the higher currents (A) in the mid-throttle range at high KV values, the losses of ESC and motor cables are higher, which results in heat on the ESC and the motor cables.

The average throttle decreases with a higher KV value, since the pilot can not necessarily fly the track faster with a higher KV value.

Of course, nowadays, no one would consider using 2S or 3S LiPo batterys on their 5“ racers.
It is more likely to use 6S to have lower currents and so less losses.
But if you choose the motor KV so that you mostly fly half throttle on 4S, the efficiency is almost like with 2S.

Choose the motor KV considering only the full throttle you really need. Your setup will be more efficent the lower you can go. These losses do also result in a higher consumption. By choosing a more efficent setup you might be able to use a lighter battery.
You should consider whether you really need a motor with higher KV value to be faster in full throttle passages, or whether you prefer to be more efficient and lighter on the track.

How do you see the current trend for high KV values and 6S? What setup do you fly? Write it in the comments!

Credits: Free Vectors via

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