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Old Jul 30, 2014, 05:27 PM
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Joined Apr 2008
165 Posts
How to Size a Brushless Motor


I am looking for information on how to size a bush-less motors for a particular boat and the reason that I am asking in the fast electric side of the hobby I figure that if any one would know how to size both the motor and a battery it would be the fast electric crowd. The boat I am building is a Dumas Sub Chaser. it is 37.5" long and 4.75" wide and built with one prop. I am going to be installing three props as were the full size Chasers. Since is getting hard to find good small motors and that I have had such good luck with brush-less motors in my RC aircraft I am thinking that is the way to go also.

So after all that I guess the question I am asking is there a formula to determine that for a prop of such and such size, you need to use this size of a motor with this much wattage and this much KV? Is there a formula that will tell me this information?

I plan on running a separate BEC, but would I be better running three batteries or would I be better to run one larger battery?

Confused in Portland
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Old Jul 31, 2014, 01:34 PM
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Joined Apr 2014
25 Posts
Greetings once again,

Dose any one have a suggestion as to where I might find how to size a brush-less motor to a propeller or if there are some kind of "Rule of thumb" for this kind of thing? Some where I would have thought that there would have been some kind of formula where for this size prop you need this size motor with this number of amps and this size battery. So how do the guys running fast electrics figure this stuff out?

Still confused in Portland,
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Old Aug 02, 2014, 08:15 AM
Steps? What steps?
zozer's Avatar
United States, TX, Humble
Joined Jan 2010
218 Posts
Andre, this is a racing boat forum, most of us use motors which give far more speed than your scale boat can use. I suggest you visit one of the scale boat forums, I think you will get more help. Good luck with your project!

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