understanding brushless motors

[toofast]

30-40

[SweetAccord]

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.

[/COLOR]

In addition to this as Jay stated, you may also determine the speed of the KV of the motor in question by multiplying the kv of the motor by the voltage:

ie: 540/2200kv motor would be 2200x14.8=32,560 rpm at the shaft. More voltage with the same motor will increase the rpm as well ass less voltage will decrease the rpm.

So with Jay's Sport running - 20,000 - 30,000 and Oval racing - 25,000 - 35,000 that puts you above sport running and at conservative Oval racing. Good place to start.

[toofast]

Thanks for the good advice everyone. Sounds like I have the right stuff, I just have to get everything dialed in.

[dana]

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.

im running this exact motor/esc/prop setup in my mean machine with two 2s 40c lipos. im getting wayyyy over 30s. its alot faster than my totally stock ul-1 with 40/52/3 prop. whats the timing set at on your motor? should be 15 degrees

[SweetAccord]

Also important to know about brushless motors that is common sense:

The amount of Torque per ampere depends on the motor's Kv.
The higher the Kv, the lower the Torque per ampere.

High Kv = Low Torque per ampere
Low Kv = High Torque per ampere

For the same Torque:

High Kv - needs more Current
Low Kv - needs more Voltage

[Flying Scotsman]

You have some very good advise, but your setup is critical to performance...prop...strut...drivetrain etc.....welcome to the wacky world of FE boating

Douggie