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What does KV rating mean on brushless motors?

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Old 04-06-2009, 06:53 PM
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skrez
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Default What does KV rating mean on brushless motors?

Hi Guys,
Can you tell me what KV rating means? If I have a 480 E-flight motor , one with 960 kv the with 1260. For what application would one be better suited then the other? Does the higher KV motors turn smaller props at higher rpm? Thanks in advance.
Frank
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Old 04-06-2009, 07:03 PM
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Default RE: What does KV rating mean on brushless motors?


Quote:
ORIGINAL: skrez

Hi Guys,
Can you tell me what KV rating means? If I have a 480 E-flight motor , one with 960 kv the with 1260. For what application would one be better suited then the other? Does the higher KV motors turn smaller props at higher rpm? Thanks in advance.
Frank
KV rating means 1000 revolutions per volt. So, a 960KV rating using 10 volts will turn a suitable prop 9600 rpm's. A 1260 KV would turn 12,600 rpm's.

Each motor has its own limit, expressed in watts, and usually comes with recommended prop and battery voltage ranges.

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Old 04-06-2009, 07:54 PM
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Default RE: What does KV rating mean on brushless motors?

No, no, no! The Kv relates to no-load rpm! Under ideal circumstances a motor of, say, 1000Kv @ 10v will try to spin (no-load) at 10,000rpm, but there are always losses so it won't quite make that. Put a prop on the motor and it will never reach anywhere close to 100% of Kv x V... with a tiny prop it might get in the 90%'s, but the "rule of thumb" loading would have a motor spinning a prop at around 70% of Kv x V.

In your sentence: "a 960KV rating using 10 volts will turn a suitable prop 9600 rpm"... if you had inserted "try to" between "will" and "turn"... then you would have been correct.

As far as "how do we use Kv" the initial poster has it correct: for the same power-in....high Kv motors are used to spin small props at higher rpm, low Kv motor can turn larger props at lower rpm. Higher Kv motors can also be geared down to turn big props.
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Old 04-06-2009, 08:13 PM
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Default RE: What does KV rating mean on brushless motors?

Thanks for explaining that in simple terms for me . I what to built a 6lbs. + twin Mosquito by BH Models and was trying to decide what would be the best motors. Some people have used the Turnigy 35-36B 1300kv motors with 9x6 props on 3s5000 lipo. I`'m thinking maybe that motor or the 35-36C 1100kv with 9x6 props, perhaps maybe get appox. 1 minute more of flight time? I`m thinking that the 1100 kv would use allittle less battery? Is this correct?
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Frank
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Old 04-06-2009, 09:33 PM
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Default RE: What does KV rating mean on brushless motors?

Yes, it should draw fewer amps and thus get you longer flight time... but with less power... will that be enough?
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Old 04-07-2009, 04:58 AM
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Default RE: What does KV rating mean on brushless motors?

Dr Kiwi,
People using the 1300kv had lots of power to spare since the motors are equilate to 25-30 glow engine in 6lbs. plane. Would the 1100 be alot less power ?
Frank
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Old 04-07-2009, 04:32 PM
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Default RE: What does KV rating mean on brushless motors?

A 3536-1100 may draw less than 20A on 3s with a 9x6... my "rule of thumb" would equate a .25-.30 glow with 500W-600W... there is no way a Turnigy 35-36 1100 can cope with, nor deliver, that much power. [I must say that I have not run a Turnigy 3536 -1100... but a GPS 3536-1100 is much the same motor, and my tests indicated it was good for only 25A-30A max before it got too hot]. To get 600W on 3s you obviously need 55A-60A.

An E-flite 480 is optimistically rated for 275W, so it is well below the 500-600W target for a 6lb plane.
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Old 04-07-2009, 05:08 PM
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Default RE: What does KV rating mean on brushless motors?

Thanks again for your reply Dr. but this is a twin motor airplane. I`m looking for the 600-700 range with two motors.
Frank
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Old 04-07-2009, 07:44 PM
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Default RE: What does KV rating mean on brushless motors?

Whoops... I missed the 6lb Mosquito!

In that case, you will need to push two 3536-1300 Turnigys fairly hard to get you into the 600-700W range - you may well need larger props or 3-bladers to draw 30-35A though, because I doubt that a 9x6, even on the 1300 will draw more than 25A.

I wonder about the Turnigy SK 3536-1400 - here are some figures from the HC Reviews which seem believable:

11.5V JM9x6 350W 11718rpm 1400g
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Old 04-08-2009, 04:59 AM
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Default RE: What does KV rating mean on brushless motors?

I`m wondering if two E-flite BL15 motors , 10-6 props,and 40 a esc. would do the trick? I would still like to stay w 3slipo if I can.
thanks,
Frank
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Old 04-08-2009, 08:51 PM
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Default RE: What does KV rating mean on brushless motors?

kv is simply the number of rpm the motor will spin at no load for every volt of input. It has no direct bearing on the power of the motor, or the amps drawn by it.

Higher kv number therefore means that the motor will spin faster for any given voltage input and therefore, if you consider two motors with the same power capability (amps x volts) but different kv numbers, the one with the higher number will deliver the power using a smaller prop because the prop will be spinning faster.
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Old 11-15-2011, 09:34 PM
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Default RE: What does KV rating mean on brushless motors?

I have been flying my parkzone P51d with a turnigy 3536 c for about a year now and it's still running strong. It is pulling 59 amps at full speed running an APC 9X6E. I'm using 2.2 amp 25C lipos and can run as many as 8 packs back to back with out the motor getting "hot" (I can hold the motor in my hand for 20-30 seconds but I've never used a temp gun on it). The motor is not rated for this but it handles the load flawlessly. Am I asking for trouble with this set up?
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