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-   -   Problem with brushless motor (http://www.rcuniverse.com/forum/speed-electric-109/11240040-problem-brushless-motor.html)

thunder.in.paradise 09-25-2012 12:36 AM

Problem with brushless motor
 
Hello

I got a problem with my custom cesa 1882 build.


The motor doesnt rev up to its maximum at full throttle, should i do some esc programing for the motor timing? or could it be a transmitter problem. I know i am using only a 4s lipo, but shouldn´t the motor rev up close to 45 000rpm on a 4s?
As it is now it feels more like 10-20 000 rpm. The boat wheight like nothing since it is a ABS hull.

All parts are newly bought from hobbyking.

Thanks for any help :)
<span style="text-align: right; font-size: larger; ">

My specs are:

</span> <span style="text-align: right; font-size: larger; ">

Hull: Cesa 1882 </span> <span style="text-align: right; font-size: larger; ">
92cm long
22,5cm wide
</span><span style="text-align: right; font-size: medium; ">0.7kg (only hull)
1.4kg with everything or 3 pounds </span>
<span style="text-align: right; font-size: medium; ">

</span>http://images.rcuniverse.com/forum/u...91/Zq97554.jpg (Boat on the picture is not mine but same type of hull)<span style="text-align: right; font-size: medium; ">





</span>http://www.hobbyking.com/hobbyking/s...alog/25091.jpg<span style="text-align: right; font-size: medium; ">
LinkMotor: 3660SL
</span><span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; border-bottom-width: 1px; border-bottom-style: dotted; border-bottom-color: rgb(0, 255, 0); cursor: pointer; ">Kv</span><span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">:</span><strong style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">3180rpm/v
[/b]<span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">Diameter:</span><strong style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">36mm
[/b]<span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">Length:</span><strong style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">60mm
[/b]<span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">Shaft diameter:</span><strong style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">5mm
[/b]<span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">Max voltage:</span><strong style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">18V [/b]<br style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; " /><span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">Max current:</span><strong style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">94A
[/b]<span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">Idle current:</span><strong style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">2.7A
[/b]<span style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">Weight:</span><strong style="font-family: Tahoma, Verdana, Arial; font-size: 11.199999809265137px; ">280g[/b]




http://www.hobbyking.com/hobbyking/s...arine-120A.jpg
ESC:
LinkTurnigy Marine 120A

<div style="color: rgb(51, 51, 51); font-family: Verdana, Arial, helvetica; "><span style="font-size: small; ">Constant Current:120A
Burst Current:240A
Resistance: .0007ohm
Battery:2-6S<span style="border-bottom-width: 1px; border-bottom-style: dotted; border-bottom-color: rgb(0, 255, 0); cursor: pointer; ">Lipoly</span>
BEC:3A/6v
Motor Type:Sensorless Brushless
Size:94 x33 x 18mm
Weight:91g</span></div><div style="color: rgb(51, 51, 51); font-family: Verdana, Arial, helvetica; "><span style="font-size: small; ">*Speed: 100,000+rpm(2 Pole)

Lipo: KyPom K6
4s 5800 35c<br type="_moz" /></span></div>
Prop: 50mm 3 blade Aluminium CNC (P1.4/3x3)<strong style="color: rgb(255, 255, 255); font-family: Verdana, Arial, Helvetica, sans-serif; font-size: small; ">50http://www.hobbyking.com/hobbyking/s...alog/25602.jpgm

m 3 Blade Aluminum CNC Boat Prop (P1.4/3x3)[/b]<br type="_moz" />

martno1fan 09-25-2012 03:02 AM

RE: Problem with brushless motor
 
Hi one thing i do see thats might bea problem is your prop,thats a big prop for a high kv motor on 4 s.I would have thought a 42 mm prop or arround there would work better.
Mart

thunder.in.paradise 09-25-2012 04:22 AM

RE: Problem with brushless motor
 
Yes i realized that after some reaserch and i bought a couple of new octura props.

But there is something else, the motor suddenly drops in output when in full throttle, its losing like half of its power. Could it
be the low voltage cutoff? the esc is cold as ice and the motor too is very cold.

The battery is the only thing that isn't completely new. But it is fully recharged and should work ok?


Thanks for the help<br type="_moz" />

ryan_t888 09-25-2012 01:08 PM

RE: Problem with brushless motor
 
Your motor kv is far too high for 4s LiPo. [link=http://www.radiocontrolinfo.com/ElectricBoat/motor.php]Kv Selection[/link]

diy-pro 09-25-2012 09:15 PM

RE: Problem with brushless motor
 
And along with the kv being too high that means not enough torque. The system is probably pulling a ton of amps at start but is no longer able to sufficiently keep it moving at such a pace because the batteries lost the burst of initial energy. Shoot for a 1600 to 2200 kv motor and youll notice better performance for that size hull

thunder.in.paradise 09-25-2012 10:10 PM

RE: Problem with brushless motor
 
But the 3660SL motor i use is capable of 18 volt doesn't that means it should work ok with a 4s (14,8volt) ?

and since the motor size is 540 (3660) the hull length should be ok?

http://www.rcuniverse.com/forum/js/f...ular_smile.gifnoob need answers

Thanks for the help



<br style="font-family: Verdana, Arial; font-size: 13.333333015441895px; " />

ryan_t888 09-26-2012 06:27 AM

RE: Problem with brushless motor
 
Often times motor manufactures will provide you with the maximum RPM that the motor can safely handle. This is generally due to mechanical restrictions of the motor. This voltage level does not tell you the proper setup. Simply put, at that voltage with no load, the motor is fine. This applies to motors in all RC's.

It does not mention what prop to use on which hull, hull length, voltage level, ect. Which makes me wonder how you ended up with a 50mm prop? That would be no where close to the correct size at that voltage and it could be very dangerous and costly picking a prop size from a hat.

Not only is the motor KV too high but the motor size is too small for a hull that large. 6s LiPo would typically be chosen for a hull that large. Then follow the methods described in the link above.

thunder.in.paradise 09-26-2012 07:07 AM

RE: Problem with brushless motor
 
I am helping my father with his boat project, so how he ended up with a 50mm prop i don't know.

But as for the hull size and motor, in your guide you describe a 36 size motor works well with 55cm to 86cm hull and since the cesa is only 6 cm longer and weight about 0.7kg, so we thought that it would be ok since it is so much lighter than glasfiber hulls.

I have gone trough your guide completely a couple of times and with some live experince i think we will manage somehow.:)

As for the hull, my father have a couple of different hulls and the cesa is the smallest one we could find in the garage.
He used to play with gas boats and most of them were really big.


We tested the boat today with a proper 4s lipo and a alu 2 blade 42mm prop

the boat were incredible fast and the motor is to strong for the hull, at half throttle from standing still the boat jump off the water.
At a straight line with no waves at all we could manage 2/3 throttle without any chrashes. I will check tomorrow with gps how fast it is.

We only run for 15min and i checked the temp afterwards and everything were really cool, you could touch everything without problem.



As for the first problem mentioned in the begining of the thread, that were simply a old broken 4s lipo situation and the over sized prop.


We want to buy a proper hull for the 3660Sl 3180kv motor so any suggestions is welcomed


And Ryan thanks for the advice so far :)
<br type="_moz" />

ryan_t888 09-26-2012 07:18 AM

RE: Problem with brushless motor
 
I would do the opposite. Find a better motor for the hull. That motor is best suited to 3s LiPo. If you want to use it, a 68cm hull and 3s would be a much better match. Same 42mm prop and all.

thunder.in.paradise 09-26-2012 07:29 AM

RE: Problem with brushless motor
 
Well my father is complaining about the cesa hull's quality and rigidity, he wants a fiberglass hull so a 68cm long mono hull will do :)





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