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Kv Question

Old 08-10-2005, 04:43 PM
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rfg06
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Default Kv Question

Alright, I need the lowdown on a motor's kilovolt rating. I understand that a Kv rating is the rpm a motor will spin at per volt. But what is the difference between a high kilovolt motor and a lower kilovolt motor ( Besides the rpm difference)???? I'll use the e-flite brushless park 370 brushless motor for example. There is a 4100Kv version and also a 5400Kv model. What is the difference between these motors? Thanks in advance
Old 08-10-2005, 07:57 PM
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michpittsman
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Default RE: Kv Question

There is also a 3600kv Eflite Park370 inrunner; I have one in my Ulti. Typically, the high-kv rated motors are designed more for 2S lipo power and the low-kv are for 3S power. The technical explanation eludes me. When the Eflite Ultimate first was released, 4100kv and the 2S pack were recommended; when I got mine, Horizon went to the 3600kv and the 3S pack as the way to go. Everybody pretty much stuffs a 3S pack in the plane now regardless of the kv rating....Jim
Old 08-11-2005, 12:16 AM
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jooNorway
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Default RE: Kv Question

This is the way I see it:

If you want a motor for a plane that flies fast (acro etc) then you use a high-pitched prop. Then I look for a motor with a higher kV-number.
On slowfliers and 3D-capable planes where the prop used have larger diameter and low pitch to have thrust at low speed then I want a low kV-number.

Two "identical" motors, same weight and same watt but different kV for example: The one with higher kV have "course" windings, allowing more current. Gets the most thrust at higher RPM. The one with lower kV have thinner windings, making a stronger magnetic field at lower current but would use higher voltage to get the strength.

If you want to use a gearbox you go for a high kV motor of course.

If you want a motor for a fan you go for a motor with a very high kV...

And so on.

Old 08-17-2005, 09:33 PM
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jdetray
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Default RE: Kv Question

In very general terms ...
High Kv yields high RPM and low torque, suitable for spinning a small prop on a fast plane or for use in a geared power system.
Low Kv yields low RPM and high torque, suitable for spinning a large prop on a slow flyer or 3D type plane.

The Kv rating does not relate to the battery voltage (2S or 3S) that should be used. Plenty of high Kv motors run superbly on 3S. The proper battery voltage for a power system depends on many things in addition to Kv.

- Jeff
Old 08-18-2005, 02:02 AM
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jooNorway
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Default RE: Kv Question

jdetray: Yes everything is in very general terms

But maybe the thing about "equal" motors, different kV and voltage I mentioned were too vague? Would like to use some examples, taking the AXI2826/xx motors: there are three different winded variantes of them, the 2826/8 take 8-12 cells, the 2826/10 would like 10-16 cells and the 2826/12 is for 10-18 cells. Just trying to indicate that low kV-rated motors as the 2826/12 often (and in general terms) like the higher voltages. As mentioned, due to more and thinner windings.

Which in fact means we try to say the same thing, but have different entries and ways to try to state it...
Old 08-18-2005, 05:47 AM
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Default RE: Kv Question


ORIGINAL: rfg06

Alright, I need the lowdown on a motor's kilovolt rating. I understand that a Kv rating is the rpm a motor will spin at per volt. But what is the difference between a high kilovolt motor and a lower kilovolt motor ( Besides the rpm difference)???? I'll use the e-flite brushless park 370 brushless motor for example. There is a 4100Kv version and also a 5400Kv model. What is the difference between these motors? Thanks in advance
Important note on these motors. Watch the amp drawl!
Per their spec sheet. 4100kv is 6 amps MAX. The 5400kv is 7 amps MAX.
Old 08-18-2005, 05:49 AM
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ron_van_sommeren
 
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Default RE: Kv Question

ORIGINAL: jdetray
High Kv yields high RPM and low torque, suitable for spinning a small prop on a fast plane or for use in a geared power system.
Low Kv yields low RPM and high torque, suitable for spinning a large prop on a slow flyer or 3D type plane.
Assuming the same motor/stator dimensions.

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