How-To

How-To choose Motors and ESCs.

When it comes time to choose your motors and ESCs it’s all about the specs.

First you need to know what size propellers your frame allows and what size you’re going to use.
(Take a look at our How to pick your Propeller article for more guidance on propeller selection.)
Each propeller size requires a different rpm to generate thrust efficiently.
This is where the KV of your motor comes into play. KV does not mean kilovolt like many assume, it’s actually the number of rotations per volt without any load (propeller).

Then you’ve got to make sure that you’ve got enough torque to spin the propeller, this is where your stator size comes into play.
The stator is typically listed as four digits. The first two digits are the diameter of the stator and the last two digits are the height in millimeters.

The mathematics involved to determine the exact KV and stator size you should use is a lot more complex than most pilots care to worry about.

We’re going to take a simpler approach using our experience to suggest a stator size and KV range for you to explore.

Prop Size Recc. Stator Size Recc. KV Rating
3″ 1105 to 1306 3100+ KV
4″ 1306 to 1806 2500-3100KV
5″ 1806 to 2206 2300-2500KV
6″ 2204 to 2208 ~2000KV
7″ 2206 to 2208 2000KV or less

Once you get to 8″ or larger propellers there are many more stator size options but generally speaking the longer the propeller the slower it needs to be spun to generate thrust efficiently.

Now that you’ve got a basic understanding of the motor specs, speed requirements and propeller selection,  you can use the thrust charts of the motors within your range to find rough current draw estimates.

Ideally you should select an ESC that has a higher current rating than your maximum current draw with the propellers you’re using.

Some ESCs will allow you to over-draw the ESC for short periods of time but for reliability sake this is not recommended.

 

For Example, I like to fly freestyle and I want to build a QAV210, this allows for 5″ props. Because I’m flying freestyle I want a high torque motor for lots of low end punch. Thus I will be looking at the RX2206 2350KV motors for my build.

Given the thrust data for this motor I will use a 30A ESC to be safe because I want to be able to use the most aggressive 5″ propellers I can find.

Now that you have you Propellers, Motor and ESC selected you can accurately select a battery for your build.

For information about selecting batteries, click here.