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 Turns vs KV

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Guff

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PostSubject: Turns vs KV   Tue May 17, 2011 12:58 pm

I remember reading an article a while back about BL motors and it said that the term "turns" as used to describe brushed motors is no longer relevant to BL ones, and that KV accurately dictates how a motor should be judged.

It seems now that manufacturers are using "turns" more and more for motors.

How does the turn of a BL motor equate to the KV?
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Dominator
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PostSubject: Re: Turns vs KV   Tue May 17, 2011 4:40 pm

That's a good question. I hope someone can pop on here and tell us. I notice some companies use turns, others use KV, while some use both and yet the numbers between companies never seems consistent. scratch
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PostSubject: Re: Turns vs KV   Wed Aug 10, 2011 2:58 pm

that is a good question...Someone correct me if i'm wrong but I believe "turns" in a BL setup is used for sensored motors? While KV ratings are used for sensorless?
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Germanese
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PostSubject: Re: Turns vs KV   Thu Aug 11, 2011 12:19 pm

Turns - Is used for brushed motors determine the number of times the wire is wrapped around the armature.
If you decrease the turns, the motor becomes more efficient, can pull more current, has a higher RPM but with less torque.
And then the opposite if you increase the turns.

KV - Is used for brushless motors to get a little more accurate rpm data. it stand for RPM per Voltage applied.
So a 5000kv motor with a 2S lipo battery would equate like this: 7.4 x 5000kv = 37000 rpm roughly.
The same still applies, more RPM equals to less torque and vice versa.

Note: Both motors can gain back torque/rpm with different designs. Brushed would have Single, Double, Triple Winds to increase and decrease RPM/Torque. Brushless Motors use different Poles designs, Singe Double Triple Poles to increase and decrease RPM/Torque Further more.

KV vs Turns
Well they both have there place and time. What they seem to have done is turn the term Turns into a rough estimate for brushless now.
Like 8.5t can be anything between 5,300kv to 5,600 Kv. Depending on the manufacture a 17.5 could be anywere between 2,500 to 3,100 kv.
So you now tend to look at Turns as a rough ball park. And this has not been noticed even back then in the days 2 different motors with the same turn could have 2 different rpm. If you buy a LRP Brushed 7.5T motor it would also tell you 46,400rpm @ 7.4v another brand 7.5T could have 45,300rpm @ 7.4v.

The only difference nowadays is that the brushless can take more Voltage SAFELY compare the brushed. So the 3.2v-7.4v limitation on standard motors is not existing no more. Hence the KV rating so the buyer now has to calculate their own RPM via the KV and how much voltage they want to use.

The other reason of the emerging KV rating is also battery changes. we used to have 6cell 7.2v nimh which are now replaced by 2cell 7.4v lipo.
So what ever battery you would be using will also change the RPM rating of your motor. 7cell nimh has 8.4v, Lipos with 3cell are 11.1v

So there is no better or worse indication which one to use, its what you are looking for in Data.
For the best result of hunting down the correct motor.
You need to know what RPM you want, which in this matter you need to KV and your Voltage.
Than in turn will give you a rough RPM number you can go by. Most higher end Brushed motors always had a little sticker indication what RPM they have at 6.0 and 7.2v this will give you a rough base to go buy with the new motors if you seeking the similar RPMs with more efficiency Brushless technology.

Hummm damn my head hurts now, this is just a small basics of these damn motors, ask Snelliman for more info.
Correct me if I am wrong or miss interp. something.

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PostSubject: Re: Turns vs KV   Fri Aug 12, 2011 11:15 am

Holy crap dude! I understood what you said and at the same time I didn't understand anything. lol!
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PostSubject: Re: Turns vs KV   Fri Aug 12, 2011 3:41 pm

You didn't mention about the different winding patterns (delta wound v. wye), which also makes a huge difference. My understanding frmo talking to some manufacturers is that turns is still just that, the number of turns of wire. But, the patern, and whether it's a 4 pole motor, etc. make a huge difference. So, I have a 5 turn delta wound motor that's a 3700 kV motor, but I have a 9.5 turn wye wound motor that's a 4200 kv motor. That's a big difference, and why comparing kV is still the best way to go with BL motors IMO.
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PostSubject: Re: Turns vs KV   Fri Aug 12, 2011 10:25 pm

Yeah like i said before there are a lot more factors. I just barely scratched the surface of the technology of these motors.
I just gave the basic most common known information, There is the rotor size, rotor magnet type, Rotor type and the list goes on.
Lets say say a perfect motor can be very expensive, and headachy to obtain. There are many factors that define the power of the motor.

As cjt just added, type of winds can also be another factor.

All I have to say have fun finding the correct motor =D LMAO
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