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nova801428
09-19-2005, 05:53 AM
I am new to brushless. I am buying a pocket combat wing from aller.com and I am going to put a Feigao brushless motor on it. but which one do I choose 4100KV 5300KV OR 5800KV, please help me I am new?

timocharis
09-19-2005, 07:08 AM
nova,

kV, KV, or Kv depending on the typist means rpm/volt. So if you have a 4100 kV motor and a 2-cell LiPo (which will generally deliver just a bit under 7 volts at load) the motor will turn about 28000 rpm max. This is one of three figures you can use to calculate the characteristics of a motor, but in more general terms you can get an fair idea using kV alone.

For example, at about 1000 kV you'll generally be talking about an outrunner than can turn a fairly large prop direct drive (say, 10x4.7 or so). Your examples for the Feigao indicate a motor that would generally be geared or use a very small prop.

Getting past theory and into your specific question, the 4100 is probably the right choice. You can run it 2s with a GWS 3030 prop direct drive, or 3s with a 3020. The 3s setup will be thrustier and a bit faster. You might like one or the other better.

You could also run one of the faster motors 2s with a 3020, but that's a load and the result might be fried wire.

Why the k in kV? I don't know!


Dave North

olmod
09-19-2005, 08:28 AM
The higher the KV the smaller the prop as a general rule of thumb
and the K represents rpm's to find the KV of a motor you need to run it at no load and tacho it using a piece of tape or similar on the drum or something attached to the shaft and running the motor flat out, then you divide the rpm you got by the voltage = KV :)

Dr Kiwi
09-19-2005, 10:46 PM
I am new to brushless. I am buying a pocket combat wing from aller.com and I am going to put a Feigao brushless motor on it. but which one do I choose 4100KV 5300KV OR 5800KV, please help me I am new?

Just to add: IMHO the 5300Kv is the best and most useful of those 12mm Feigaos. You could also look at the 12mm 5300Kv Medusa Afterburner http://www.medusaproducts.com/Motors/012.htm

Cheers, Phil

timocharis
09-20-2005, 05:44 AM
Phil,

What prop are you running dd with the 5300?

Dave

Azarr
09-20-2005, 11:39 PM
nova,

Why the k in kV? I don't know!


Dave North

FWIW, the correct term is Kv. "K" is the scientific notation for a constant with "v" standing for volts.

Dr Kiwi will probably chime in, but the guys at NEAT were running the GWS 3 x 2 with 2 Lipo's on the Medusa 5300 Kv motor.

Azarr
www.ecubedrc.com (http://www.ecubedrc.com)

Vamooska
09-21-2005, 01:18 AM
Yup...that is the setup for sure. Be sure to use at least Deans micro connectors too.
Azarr...nice meeting you at the NEAT.

Vammy

timocharis
09-21-2005, 01:28 AM
Azarr:

> FWIW, the correct term is Kv. "K" is the scientific notation for a constant
> with "v" standing for volts.

Wow, that's the last of the options I would have considered likely! Shows you what I know. Any idea why the lower-case "v" convention in this case when the IEEE (and others) officially designate a volt as Capital "V"?

I habitually type kV (with doubts) because that's the accepted standard for kiloVolt. As in eV for electron Volt. Etc. Dunno why that was decided, but I do have a copy of the LS-145 standards lying around (okay, it is government, but IEEE and all...)

I must admit I've not come across the convention for "K" as a sort of universal constant before (of the foo or bar sort). Oh sure, there's Boltzmann's constant, or degrees Kelvin, or the conservation of energy, et al, but they're all specific. Nor do I recall that from my dimly-remembered schooling. What discipline?

Well, let's take a quick glance.

Hmm. Here's a motor references (M.I.T.) implies that "K" has historically been used as a catch-all for "motor constant" (no, I didn't study motors in school) with various subscripts used to denote the particular flavor, such as KT or KV, with the trailing letters properly written below the baseline.

That would certainly support your point! It would be a special case of V not being lower case, but rather a subscript in the motor constant convention! (If I'm reading the reference right. Typical horrendous tech writeup).


Dave North

ForestCam
09-21-2005, 02:02 AM
While we're at it, why's the symbol for gold Au?:confused: :D

timocharis
09-21-2005, 02:28 AM
I think that's from the Latin aurum, for gold. Back when they made the periodic table, it was way cool to do everything in Latin. But for some reason, not all the elements were done this way ... no, I don't know the "reasoning" behind that, either!


Dave

ron_van_sommeren
09-21-2005, 07:25 PM
The higher the KV the smaller the prop as a general rule of thumb...Assuming both motors have the same dimensions/stator/magnets.

Blob_master
09-26-2005, 02:09 PM
So what does Kv mean in relation to power output? eg if you have a 1000kv motor, running on 11 volts, ie 11000 rpm with no load, what prop can it take and what thrust will it produce?

Matt Kirsch
09-26-2005, 06:39 PM
There's no way to tell with only that information. You could have a 1000Kv motor the diameter of your little finger, or you could have a 1000Kv motor the diameter of your head... Each would be able to spin a different size prop and put out a different amount of power on an 11V input. That's because the bigger motor has thicker wires that can handle more Amps, and larger, stronger permanent magnets.

Simply put, a higher Kv spins the prop faster. It takes more power to spin the prop faster, and a faster-spinning prop produces more thrust. Therefore, you can say that the higher-Kv motor is "more powerful," in some cases, but you have to keep in mind the limitations of the motor, ESC, and battery.

An example of where this breaks down is the case where you're maxing out a battery with a 1000Kv motor. If you pull the 1000Kv motor and drop in a 1200Kv motor of the same design, you'll probably ruin the battery because the 1200Kv motor needs to draw more Amps to turn the prop at a higher RPM.

Another example is if you have a 25A ESC, and you're drawing 24.5 Amps with that same 1000Kv motor. If you swap in a 1200Kv motor, the ESC will burn out because the higher Kv motor is drawing way more than 25 Amps.

Commander_Drake
10-28-2005, 05:39 PM
While we're at it, why's the symbol for gold Au?:confused: :D

A lot of the chemical symbols come from Latin names. For example Pb for lead which is plumbium in latin. Hence our term "plumber".

Sorry about the off-topicness.