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Old Apr 27, 2013, 06:01 PM
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motor (kv) question

Sorry for the dumb question, ....but here goes.
I have acquired a used motor from a friend. He doesnt remember what kv the motor was. He just remembers that he bought it from Grayson hobbies (I have tried for months and cannot contact) .
I DO know that the motor is a 35-30-08
How can I determine the kv? Thanks in advance!!!
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Last edited by Dale Young; Apr 27, 2013 at 06:25 PM.
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Old Apr 27, 2013, 07:47 PM
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Borrow a tach and mark the motor bell with tape or a sharpie to allow a reading to be taken. Measure the unloaded (no prop) RPM at full throttle. Kv is then measured RPM/Esc input voltage. For example, 10000 RPM / 10 volts = 1000Kv. This will be close enough for government work.
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Old Apr 27, 2013, 08:07 PM
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Can you post a pic? Maybe someone has seen it or one of us can find a match using google images.
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Old Apr 27, 2013, 08:55 PM
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Chattanooga, Tennessee, United States
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I can't place any Grayson motor of that size, but if it is about 75g 3530-8T, then it is probably about 1250-1300Kv...(an HXT 3530-10 I tested was ~1085Kv)... but wait a Turnigy 3530-14T came out at 1450Kv... so maybe yours is closer to 2000Kv???

Aha.. An 80g EMP 3530-08... which is an HXT motor anyway.... is said to be 1700Kv.

http://mayor-hobbies.net/RC/pages/info/emp_35-30.html
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Last edited by Dr Kiwi; Apr 27, 2013 at 09:16 PM.
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Old Apr 27, 2013, 08:56 PM
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Thanks for the replies guys!! At the moment, I'm on a business trip and I'm not close to it. But I'll try posting a pic when I am. Thats a good idea!!
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Old Apr 27, 2013, 08:58 PM
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Whitecrest, That sounds like a great idea, but will running it unloaded, hurt it?
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Old Apr 27, 2013, 09:59 PM
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No. To be extra safe, use 2S or 3S to limit the maximum RPM and only run for a few seconds; long enough to measure the RPM. It will draw very little current running unloaded.
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Old Apr 27, 2013, 10:39 PM
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Thanks!!
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Old Apr 27, 2013, 10:48 PM
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Dr. Kiwi. That particular motor seems to be alot smaller( or at least alot shorter) than the one I got. It is golden ended, with a silver can. It also had a sticker that said Grayson hobbies 35-30-08 on the can.
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Old Apr 28, 2013, 01:28 PM
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What is the diameter/length/weight of your motor?.. maybe you have one with a 35mm x 30mm stator (not 28x14 stator and 35x30 external dimensions that I was thinking of).
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Last edited by Dr Kiwi; Apr 28, 2013 at 01:35 PM.
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Old Apr 28, 2013, 05:25 PM
Jack
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Joined May 2008
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A 35 x 30 stator would produce a motor about 7mm more in O.D. or about a 42mm O.D. on the magnet housing. The overall length is harder to predict but from the back of the baseplate to the top of the dome (not to the top of a raised boss where the shaft emerges) would be 10-12mm or so more than the 30mm stator height. So it might have been called something like a 42xx. or something like that.

Getting a weight on the motor and a raw Kv would resolve all the mysteries as far as using it, then it just a case of trying some props that need an input power of about triple the weight.

If you can't get a weight or an RPM your toy chest really need some help!

But you can put a prop on it and see if it gets hot and blows hard. If it gets hot try a smaller prop, if it does not, try a larger one. When the base plate gets warm to the touch you are in the ball park for using it.

Jack
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Old Apr 28, 2013, 07:00 PM
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I'll be back home tuesday, and will get specs then. Thanks guys!!!
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