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Posted by CygnusX1 | Jan 23, 2015 @ 09:41 AM | 3,717 Views
What I have learned in the hobby so far>

Power(Watts) = Volts x Amps

746 Watts = 1 Horsepower - for reference.

So when designing, you need to pick a motor that has enough WATTS to move your vehicle, and has approximately the right Kv (RPM) rating for your application, at the Voltage you intend to use.

What do you need?
1) Find out how much power you need. ex. 1000watts for a 22" boat.
2) Decide how many nominal volts you will use. ex. 4S or 14.8V
3) How many rev's do you need. ex. 30,000 rpm final speed for a boat prop

With Watts and Volts, you can calculate you current draw. ex. 1000W/14.8V = 68 AMPs
With Volts and RPMs you figure out what Kv you need. ex 30,000RPM/14.8V = 2030KV

Picking a motor and ESC.
4) Find a motor that has a close Kv to your need. ex. 2030Kv
5) Then see if it's rated for 1000watts, or near 68 AMPS at 4S.
6) Make sure it physically fits into your project.
7) Pick an ESC at least 20% higher than the max AMPs and Volts (4S) of your motor choice.

You will probably NOT find the exact match, but you can be conservative and get something with close specs. Never select something that can't at least handle your 4S volts, and your calculated AMPs, plus 20%.

There is more to it than this if you want to delve deeper into efficiency, but for practical purposes, and for the layman, this will get you a good setup. Next you will need to select props or gearing if it's a car or if you need to change your final drive RPM's. That's another topic.

Leopard Motors does it Correctly! KUDOS to Leopard...all other motor companies, take note. ;-)
This is how motors should be rated. Look at their charts (Engineer's Dream), and pick me a motor from the data above.

I would pick this motor: LBP4042/3Y
I would pick a 100-120AMP ESC that can handle 4S or more.