Choosing motors for your multi or quad copter can be daunting. With all the manufacturers and middle-men and retailers providing wordy descriptions and fanciful names to attract your attention; it can all be very confusing!
This article is not going to try and de-mystify the complex relationships between motor specifications, propellers speed controllers and power sources, I'm sorry if that disappoints.
Reality is there are many articles available that explain the impacts and dynamics of the variables around power-trains, and honestly unless you're a mathematician or physicist you probably won't understand the half of it; I know I don't.
Reality is that you don't really need to 'know' it all, rather just know some key things to look for and where to go to make good choices based on the more scientific algorithms and people that know how to work it all out.
So where do you start?
I'll qualify all of this with the fact that I am no expert BUT I have built many many multirotors, have flown many more and enjoy surfing the net and finding stuff out that makes life easier... So here is how I go about choosing motors.
1. Frame manufacturers and distributors.
Most of the time a quality frame builder will design the frame with a specific purpose in mind and most often a specific power plant in mind. Therefore, they will often recommend an ideal motor if not specifically by brand and model by size and Kv or RPM.
If it is the case that they are recommending something specific then it is highly likely if they don't sell it themselves they could provide you information about where to acquire.
A word of advice - Make sure the recommended combination of battery, ESC, motors and props are available, I have seen and experienced not being able to buy the recommended combinations from anywhere so if you can't find the recommendations for sale after a simple search I would be cautious about proceeding with the frame.
2. Understanding the basics.
Have you have ever wondered what all the numbers are on the side of a motor or for sale description? Well there are a couple of sites that I visited that made the basics so simple that it's not worth trying to re-create the wheel so for your reference here are a couple of links worth visiting to work it all out for yourself.
Brushless motors - how they work and what the numbers mean
Painless 360 Motor Basics
3. Use a tool that helps you choose the right motor, power, props and electronics.
Someone else has done the hard work and has been kind enough to make it available to us all. There is one very well known tool called eCalc and a not so well known one without a name. I find them both useful although I would recommend the "no-name" one. From personal experience the no name version tends to give you what you need as far as information and then leaves you to make your own choices. eCalc is also a great tool but I almost feel like I'm being pushed towards specific brands which is OK but the sceptic in me sees an ulterior motive that may skew results. On the other hand, its a good tool with a built in motor database and it's so cheap it might as well be free.
Both are worth a look and make up your own mind:
All in all, you can spend a lifetime surfing the net, thousands working it out trial and error and follicles as your trying to peace it together. The links and couple of tips should be enough to get you started in the right direction. As you become immersed you will find other likeminded people to help, copy from and hassle your way to a better performing drone. Remember too that there are many other components to consider not just the motors!