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Old 02-06-2013, 07:47 AM   #1
charles nitrotek
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Default What is KV

Hey Everyone:

I have started building foam airplanes for the last 2 months and getting help from my old boss, but since he laid me off. I lost my bosses help for the airplanes I am building. Okay, here is my questions

1. What is KV?
2. How do I determine the size of KV for the plane I am building?
3. Does KV determine the size of a Prop....

Thanks in advance.....

Charles
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Old 02-06-2013, 08:38 AM   #2
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Hi Charles. Welcome to WF!

KV is how many RPM per volt a motor will turn with no load (propeller, fan, whatever) on it. A big factor in prop choice. Beyond that, I'm pretty much lost myself, but here's some reading for you:

Everything you wanted to know about electric powered flight

When it comes to choosing power systems, I find motors that give info like the props it should use and how many amps it will pull with each prop, etc.

Enjoy the reading!
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Old 02-06-2013, 09:24 AM   #3
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Kv is only one of the parameters of a motor.

Generally you choose the amount of power you want first based on the weight of the plane and type of flying (trainer, aerobatics, 3D etc). When you've got the basic motor power then you need to think about the battery you're going to use and the motor's Kv.

But Kv does affect prop size. Simplifying a bit, lower Kv = larger prop turning slowly, higher Kv = smaller prop turning faster.

Steve
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Old 02-06-2013, 12:20 PM   #4
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So over-simlifying and generalising:
You figure out how many watts the plane needs based on it's weight and desired performance envelope. You decide the maxim size of prop you can use (based on ground clearace etc.) Then you go looking for a motor and battery combination that will give you your watts (plus a margin of error) while spinning your chosen prop.
Use the manufacturers data or programs like eCalc to figure it out.


Big props work best for most planes with the exception of high speed models where you might have to go for a smaller prop spinning at higher RPM.
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Old 02-06-2013, 09:59 PM   #5
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Charles.....

KV =

kilovolt - a unit of potential equal to a thousand volts
kV
potential unit - a measure of the potential energy of a unit charge at a given point in a circuit relative to a reference point (ground)

V, volt - a unit of potential equal to the potential difference between two points on a conductor carrying a current of 1 ampere when the power dissipated between the two points is 1 watt; equivalent to the potential difference across a resistance of 1 ohm when 1 ampere of current flows through it.

Hope that helps ya...........
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Old 02-07-2013, 12:36 AM   #6
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But, this KV isn't that KV...

Ask me why your DX5e is doomed... and how to fix it.
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Old 02-07-2013, 01:32 AM   #7
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Originally Posted by charles nitrotek View Post
Hey Everyone:

I have started building foam airplanes for the last 2 months and getting help from my old boss, but since he laid me off. I lost my bosses help for the airplanes I am building. Okay, here is my questions

1. What is KV?
2. How do I determine the size of KV for the plane I am building?
3. Does KV determine the size of a Prop....

Thanks in advance.....

Charles
KV is just an indication of how fast a given motor will turn over with a given battery voltage and reasonable propeller. In theory, a 600 KV motor will turn a reasonable propeller at 6000 RPM on a 10 Volt battery. (600 times 10 Volts.)

The main parameters of these brushless motors is KV, Amps at no load, winding resistance, and motor weight.

You could have a tiny one ounce motor with 400 KV that would turn perhaps a 6 inch propeller at 7000 RPM. That 6 inch propeller might blow some of the papers off of your desk. Or, one of my big 25 Ounce Hacker A60 motors that will turn a 19 inch propeller at 7200 RPM. That 19 inch propeller will clear everything off your desk, including any models that might be on it! Big difference!

Similar to an electric drill motor that turns over at 10,000 RPM, versus one of those Indy 500 race cars with 800 HP that also turns over at 10,000 RPM.

What helps in what you're trying to do is one of those computer programs. One good one is www.motocalc.com, free for 30 days, then $39. This program allows you to input model wingspan, wing area, model weight, motor mfg, battery and prop size, and let you know if it will fly, and how well it will fly. Also lets you know if the motor is being pushed to hard so as to burn up its windings. Or if you've got way to small of a propeller on the motor, making for real inefficient operation.

DennyV
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Old 02-07-2013, 03:10 AM   #8
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Originally Posted by CNY_Dave View Post
But, this KV isn't that KV...
<nitpick>Actually, kilovolt is spelled kV and "our" Kv is spelled Kv.</nitpick>

AMA #959089
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Old 02-07-2013, 02:59 PM   #9
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Originally Posted by NJSwede View Post
<nitpick>Actually, kilovolt is spelled kV and "our" Kv is spelled Kv.</nitpick>

"You are technically correct- the best kind of correct"
- Hermes

Ask me why your DX5e is doomed... and how to fix it.
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Old 02-07-2013, 04:36 PM   #10
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Originally Posted by bpj1980 View Post
... Anyways, buy for now and enjoy your flying, i look forward to reading advise, tips and any form of help i can ...
Very handy/instructive tools and calculators, wiring diagrams, demos:
The Script Asylum
-> RC calculations
-> electrical


E-flight 101 by RCG member Ken Myers, will at least save you a ruined LiPo (or worse!), a burnt motor and a fried ESC:
The Ampeer
-> Electric Power Basics

followed by
The Ampeer
-> Everything youw wanted to know about e-flight (Ed Anderson)
Table of Contents
  • Six Keys to Success for New Pilots
  • Important Note About Motor and Propeller Safety
  • The Mythical Best First Plane
  • The AMA Park Pilot Program
  • Things To Check On a Ready-To-Fly (RTF)
  • What You Need To Know About Receivers
  • What function goes on which stick?
  • Battery Basics
  • Amps Versus Volts Versus C
  • Lithium Battery Chargers
  • Balance chargers versus external balancers
  • Extending Flight Times While Maintaining Balance (proper CG)
  • Understanding the Electronic Speed Control (ESC)
  • he Low Voltage Cutoff Feature (LVC) Of Your ESC
  • The Role of the Battery Eliminator Circuit in Your ESC (BEC)
  • Sizing Power Systems for Electric Airplanes
  • Prop Versus Amps
  • Why Consider a Gearbox?
  • What Do the Kv Numbers On Motors Mean?
  • Who Needs a Wattmeter/Power Meter?



Bruce heeft nog veel meer nuttige filmpjes voor modelbouwers op zijn geweten, meer dan 100, niet alleen over accu's:

www.youtube.com/user/RCModelReviews/videos
Idem zijn site
www.rcmodelreviews.com


LiPo storage
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


All about LiPo's
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


LiPo charging, 4-button charger
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


4-button charger, loading & saving data
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


What't inside a 4-button charger
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


ombouwen PC voedingen
DIY: using a PC power supply
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


Switching charger to other batty type
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


Accucel 6 charger
YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.

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Old 02-07-2013, 06:35 PM   #11
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"<nitpick>Actually, kilovolt is spelled kV and "our" Kv is spelled Kv.</nitpick>"

LOL....kinda knew that....just threw it out there since the ? was KV....lol

Good stuff Ron Van!
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