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One of the mistakes pilots makes when they build their first drone is they use too small motors. People think that if a motor works fine with 5-inch props, it will work with 7-inch props as well. It's not true. In this longish video, I will tell you how to choose motors for your drone: 5-inch, 6-inch, and 7-inch. We will talk about torque, power, a moment of inertia, what happens when you put a too big propeller on a motor. And finally, some numbers that will help you pick correct motor for propeller size. Both in terms of motor size/stator volume and motor KV.
Errata: I forgot to multiply by Pi i stator volume calculations! All values are around 3.14 times to small, but at least I forgot about it everywhere! Pc in video for 6 and 7 inches are swapped, they are fine in the description.
Stator volume of different motor sizes (all values are divided by Pi, it slipped me and now it's too late to edit. Just do not multiply by Pi :) )
2204 - 484mm^3
2205 - 605mm^3
2207 - 847mm^3
2208 - 968mm^3
2306 - 793mm^3
2406 - 864mm^3
2506 - 937mm^3
2507 - 1093mm^3
2508 - 1250mm^3
Desired stator volume for propeller sizes:
5-inch props - 600mm^3
6-inch props - 700mm^3
7-inch props - 900mm^3
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How to choose KV:
KV = Pc / S
KV - motor KV
Pc - propeller coefficient
S - number of LiPo cells
Pc for different prop sizes:
5-inch props - Pc = 9600
6-inch props - Pc = 7600
7-inch props - Pc = 6400
More about a moment of inertia and KV is here
KV is a lie • Motor KV explained - K...
Moment of inertia • Video