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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 5inch props, it will work with 7inch props as well. It's not true. In this longish video, I will tell you how to choose motors for your drone: 5inch, 6inch, and 7inch. 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:
5inch props 600mm^3
6inch props 700mm^3
7inch props 900mm^3



How to choose KV:
KV = Pc / S

KV motor KV
Pc propeller coefficient
S number of LiPo cells

Pc for different prop sizes:
5inch props Pc = 9600
6inch props Pc = 7600
7inch props Pc = 6400

More about a moment of inertia and KV is here
KV is a lie    • Motor KV explained  KV is a lie and ...  
Moment of inertia    • Video