understanding brushless motors

[toofast]

Hi,
I need help with the speed of brushless motors. I have other RCs but they all have brushed motors and I understand which one is faster then the other. But not with the brushless. In my boat right now, i`m running a single 540/2200 motor on 2-2 cell 5200 lipos. It goes ok, but I want it to go faster. I know adding more battery adds speed, but, i want to up the motor first. So the question is, how do you tell which brushless motor is faster then the other?
Thanks.

[Alexgar]

What kind of boat and motor?

[toofast]

32" catmaran, God-Speed, Leopard

[toofast]

Motor is a Leopard 4074 2200

[Fluid]

While there are a lot of variables, a general set of rules exist for choosing the Kv of a BL motor. The physical size of the motor can very depending on the boat, voltage and use, but for choosing the Kv of most BL motors:

Multiply the Kv by the nominal voltage (3.7 x number of cells in series). For your 4 cell pack: 4 x 3.7 = 14.8

Sport running - 20,000 - 30,000
Oval racing - 25,000 - 35,000
SAW racing - 35,000 - 45,000

These are general guidelines but will give you an idea of where to be when choosing the motor. Until you have gained experience you should ask at least three others what they think. Do not rely on what just one person tells you. Choose your "experts" carefully.

The motor you have now is already high for sport running on 4S. We need to know what your expectations are for the cat - speed and run time. You may be able to go faster with a just different prop.



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[toofast]

I`m running an oct 640 sharpened/balanced prop. Run time isn`t an issued. I got the boat for run. I`m looking for the boat to skip accross the water instead on riding on it if that makes sense.

[Alexgar]

i tried this prop on my apparition this weekend on 4-5s on a cc 22oo kv and was extremely immpressed

http://www.offshoreelectrics.com/pro...prod=ose-80710

[marko500]

i tried this prop on my apparition this weekend on 4-5s on a cc 22oo kv and was extremely immpressed

http://www.offshoreelectrics.com/pro...prod=ose-80710

What kind of speeds did you see with that setup?
Also what is the pitch on the prop?
Mark

[toofast]

Thanks for the suggestions and help. I`ll take all I can get.

[Alexgar]

1.4 pitch no gps but faster tha my bj26 that does 44mph

[steveo]

how fast is your boat currently running , what prop , hull are you using, you can crank out quite a few more mph with a different prop and setup, give us some more info

[toofast]

Guessing at the speed, I would say it would be in the 30s . The hull is a God-Speed catamaran. 32" long. It`s a low profile hull. I put in a Leopard 4074 2200 motor. Seaking 180 amp esc. Octura x442 (thought it was a 640) sharpened & balanced. 2-2cell 5200 lipos. I replaced the factory single rudder to dual rudders. The couple times I have ran the boat, neither the motor or speed control felt warm. Runs very cool. Batteries also.

[video200]

you shuld be seeing more speed then that. are you running those batteries in series or paralell ?

[toofast]

I made a "Y" for the batteries. One of the wire leads from the speed control goes to one battery and the other wire goes to the opposite pole on the other battery. Then a wire batterey to battery to opposite poles.

[video200]

how many C are the batteries ?