# Motor definition

Hi,
I am struggling since few days with motor size
For ea, SSS56104 serie:
360kV is rated 95A and 108V
And
790kV is rated 180A and 58V

As we are all mostly using 12s setup the extra 50V from the 360kv are useless
So why people are using 360kv with a reducer instead of 790kv with a higher gear ratio?
At 50V we can have more power with the 790kV solution

Same goes for the 6384… It is rated 120kV and 120A (no gears more power )… So it seems to be a better solution than the 360kv even if it is not true

Because most of the gears are not rated 37’000 rpm at the input, they are rated 10000 max rpm at the input so with 500kv and 5:1 you are still factor 2.4 too high. It’s a compromise.
Why do you not consider a direct drive? 65152 120KV or 63100 Outrunner run wet, no hassle with gears and shorter pod.

I used 6384 in 4 Boards, he is very good for this money.
Greetings Frank

Ok so if I am correct, as the gear limits the maximum rpm, you have to limit the voltage
So, if the max rpm are 10000tr/min
Max V on 360kv ->28V-> Max P= 28V x 95A =2600W
Max V on 790kv ->12V-> Max P= 12V x 180A =2300W

Strangely the 63100 (Max 80a) seems less powerfull than a 6384 (MAx 120A) probably incorrect datas

Do you have a link for it? I have see some on Aliexpress but I am not so confident

no, you just don’t want to go too high so 790@50V ist probably too much for most gears.
I run a gear rated for 10000 rpm with 420KV sss56104 @12s. 420*50 = 21000 (idle).
It will just not last as many hours as rated but who foils 20000h

For eFoils, best prop speed is between 3000 and 6000 max RPM, that’s how I chose gear/motor combination. To get an idea, have a look at the data sheet of that Chinese gear: More Economic Gearbox options - #4 by sat_be - Propulsion System (Motor, Gears) - FOIL.zone

It still seems to be OK after 15 Sessions.

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Yes that why I mentionned “using” 790@12V to not overload the gears and then reduce the power by this limitation…
It is more clear now. Thanks
It is funny because with jet it is the opposite (with a certain limit)

Most of the time the motor specs given can just be thrown away, they come from a guess, an incorrect calculation or marketing lie, never from a dynamo test in your specific use case.
The max rating has also very little to do what a motor can take during use at is it is thermal limited. In this regard for submerged motors we are on the right side of things off course
A drenched outrunner can hardly be overdriven as the coil cooling is so effective, it’s only when you have gone overboard with the waterproofing or coils short that it burns

What you also need to consider in the motor choice is current losses for a given torque where T=(9.55/kv)*I
Say you require 2Nm, then 105A for 500kV and 165A for 790kV is needed.
Losses are the same in the motor but not in esc so it will have to cool 2.5x more watts from the higher kV motor. Many builds have issues with ESC cooling so this is best avoided.

(Then off course you could think about comparing different gearings but since the gears are rpm limited and less rpm capable for higher gear ratios it normally doesn’t work as an option.)

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what about Flipsky 6384 190KV 4000W BLDC? All builds on forum based on 120kv version.
There is only one build on forum with twin-motor 190kv configuration.

I’m interesting if with motor will suitable for teenager build (less than 60kg rider) as direct drive?

6384, 120kv drives very good for light drivers.
We used him with 6s, 30km/h and 150A ESC flycolor without cooling.
Its a nice cheap set up with 190mm prop

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and what max/flight current you have?
If cell has 30A as normal load, and 150A is a pick for motor (for example), when you should have at least 5p configuration if you willing not overload your battery? - 5p*30A=150A pick
Is my calculation right?

Flycurrent 32A
I uses 14x 6s 4000mAh =56Ah
90min for fun

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6384 on aliexpress are cheaper and have a lower kv…

That is a ton of lipo! I was planning on 12s 12Ah
Flycolor esc are really cheap… I will use it on a paddle so I probably need 12s to have a good speed… Hoping 30km/h

Is it possible to use that motor with heavier builds ?
Surfer~75kg + Battery ~ 7kg (12s12p)… ?