About motors

[pascallee]

Hello Everyone,
Another newbie here. I have tried to find answers in the forum but with no success. I have got some unanswered questions that may seem silly for you experts, about motors.
What is the difference between for example the FSD 380S 2636 and a Feigao 380 9xl 2612 apart from build quality? Both have nearly the same RPM/V and I know that the longer motor will pump more Amps and would require a bigger ESC and have more torque but how will that help when running the boat?
I am asking this as I have ordered the Red Evo which has a FSD 380 2636S and would like to know what benefit will I get if I replace it by a Feigao 380 9xl 2,612 and also what does the difference in number of turns do to the performance?
Thanks for helping.
Pascal

[Flying Scotsman]

The number of turns reflect to the rpm that the motor is capable of producing, the lower the number of turns the higher the rpm and amperage draw.

Douggie

[v-spec]

The motor in the Red Evo should run fine. I've run the F380-2858 in a couple small boats and it ran perfectly fine. I don't think it's worth it to upgrade to the same KV Feigao. If it were me I would move up to a 540 sized motor in that boat if you plan on swapping motors.

[pascallee]

Thanks for you answers. As per v-spec's advice I'll run the stock motor but my question was more about the difference length of motors keeping the same KV. What are the benefit in increased length(more torque) or bigger motor like 540 with same KV. I just wanted to know more why you boaters prefer longer and larger motors with more torque. Doesn't same KV = same speed with same size prop or does a higher torque motor runs faster under load?

[v-spec]

It's all about the torque. The longer motors let us spin more aggressive props for more speed while still keeping the RPM's temps and amps in check. And your right about the engine load.

[pascallee]

Got it now. To make it simple, we look for higher torque to use bigger prop which equals to higher speed and also a bigger motor would run cooler than a smaller one if we keep the same prop. Now I understand the reasoning.

[video200]

Doesn't same KV = same speed with same size prop or does a higher torque motor runs faster under load?

id say that with a longer motor you get more torque and you can run the same prop with less load on the motor witch again wil increase the actual rpm on the prop for the same amp spendt.

[Old Sloppy]

a small motor will asorb a small amount of heat and will spin a small prop.

a mid sized motor will asorb a mid amount of heat and will spin a mid sized prop.

a large motor will asorb a large amount of heat and will spin a large prop.

a large motor generaly will be more sturdy too.


Harry

[hammertime]

if you used a motor like a 380 and tried to spin a big prop like the sv prop it wont have the power/torque to spin it and an efficient rpm. This causes high amp draw, a lot of heat, and failure to equipment. Bigger motors will allow you to sin a bigger prop efficiently. The more load you put on your motor i.e. to big of a prop or too many volts to the motor the more likely your electronics will fail. Thats why you see a lot of guys wth bigger boats using low kv motors with more volts to them. Lower kv motors will have more tourque. You can apply more voltage to these motors to obtaine the rpm you wish to have and have more tourque from the motor to spin a bigger prop. You have to be extremely careful and find a happy medium between your voltage, prop, and load/amp draw. The higher your voltage and rpm the smaller the prop. Always start with a small prop and work your way up.

KV doesnt always mean more speed.

[hammertime]

video200 is also correct.. when i say KV doesnt always mean more speed what i am saying is a 380 motor spinning 30,000 rpm unloaded doesnt mean a 540 spinning 20,000 would be slower. It has to do with your size of the hull, weight, and prop size. If you put a sv prop on both the motors mentioned the 380 loaded could possibly only spin half of the 30,000 unloaded. This causes huge amounts of heat and current. A 540 with the same prop will be able to still spin closer to its unloaded rpm. This is efficient and will leave you with lower temps and current. Your electronics like that a lot more!! and so do your batts.

[pascallee]

Ok thanks guys, that's really clear for me now.
One more thing, does lower KV means smaller ESC?(as the amp draw is smaller)

For example lets take a Neu 1515 1Y 2200KV, the theoretical continuous power draw from the chart is 1250w and the peak draw is 2500w. We all know that Power=Current x Voltage. So if the boat is running 4s to yield 32460kv, the theoretical continuous Amp draw will be 1250w/14.8v = 84.46A and the surge Amp draw will be 168.92A, What Amp ESC would you advice and with what formula do you select it, should I take consider the continuous or the surge Amp draw when choosing an ESC?

And for this time lets say we replace the above motor with a Neu 1515 2Y 1100KV and run the boat with a 8s pack, with the same formula(Power=Current x Voltage), I will get a continuous Amp draw of 42.23A and a surge Amp draw of 84.46A. Can I use this time, a smaller ESC with half the Amp rating of the above one?

Pascal

[hammertime]

i go to school for robotics automation and control systems. I know a lot about this stuff.

First guideline. Everyone wants to save a few bucks.. understandable... but it is always better to do it right the first time. I ALWAYS buy a bigger esc than i need. It leaves room for error.

I always take consideration for surge current. Problem is there is no defined continuous load or resistance. The current running through your electrical system is all based upon
#1 weight...because the more your boat weighs the harder it is for the motor to run at an efficient rpm. The motor has to work harder to move your boat out.
#2 Prop size. The bigger the prop the harder the motor has to work to run efficiently. In order for a motor to run efficiently it has to reach an rpm close to its unloaded rpm. You also dont want to completely unload it because it pulls power away from your system. Watts=HP

ExI=P
I squaredxR=P
E squared/R=P
E squared/P=R
E/I=R
P/I squared=R
P/E=I
E/R=I
square root of P/R=I
square root of PxR=E
P/I=E
IxR=E

This is how you find anything in a system that is constant. A boat is never constant. Variables change throught your entire run. Prop in water hits a wave comes out of the water and back in. =constant current, sudden drop in current, then spike in current.

Dont push your rpm too high with a big prop out of a high kv motor. I ran an 8xl on 16.8 volts on a 100A esc and a smaller prop. 50+mph and everything was cool. I would go no lower than a 100Aesc. The bigger the better.

I know i am babling on but its hard to explain. I could go on forever.

2200kv on 3s would be better to start out with. get at least a 100A esc. Run a small prop until you reach a desired speed or temp. If its still running cool go to 4s start with a smmmaaaalll prop and work you way up until your reach a desired speed and temp. Limit your time on the runs and check temps every minute or so. Dont run it half throttle either. Creates more resistance= more A=more heat. Energy is disipated in heat

[Flying Scotsman]

Ok thanks guys, that's really clear for me now.
One more thing, does lower KV means smaller ESC?(as the amp draw is smaller)

For example lets take a Neu 1515 1Y 2200KV, the theoretical continuous power draw from the chart is 1250w and the peak draw is 2500w. We all know that Power=Current x Voltage. So if the boat is running 4s to yield 32460kv, the theoretical continuous Amp draw will be 1250w/14.8v = 84.46A and the surge Amp draw will be 168.92A, What Amp ESC would you advice and with what formula do you select it, should I take consider the continuous or the surge Amp draw when choosing an ESC?

And for this time lets say we replace the above motor with a Neu 1515 2Y 1100KV and run the boat with a 8s pack, with the same formula(Power=Current x Voltage), I will get a continuous Amp draw of 42.23A and a surge Amp draw of 84.46A. Can I use this time, a smaller ESC with half the Amp rating of the above one?

Pascal

Interesting, you asked a very basic question about what the number of turns refer to in a motor to and now you are an electronic professor.

Douggie

[pascallee]

Interesting, you asked a very basic question about what the number of turns refer to in a motor to and now you are an electronic professor.

Douggie

Professor, no, just some basic physics from my school days.