Discussion Motor formulas

 #1 fly_boy99 Oct 24, 2006 01:55 PM

Motor formulas

I thought it would be a good idea to have a sticky around motor formulas we constantly use here in the EMD&C section. If there is an error please PM me instead of posting here.

Please add new formulas as you see fit but please do not clutter this stickey with commentary. If you wish to do that start your own thread. Thank you.

=======
Efficiency

Motor Efficiency = Pout/Pin
Pout = (Vin - Iin * Rm) * (Iin - Io)
=======
Motor Kv

Kv = RPM / (Vin - Vloss)
Vloss = Iin * Rm
=======
Motor RPM

RPM = Kv * (V - Vloss)
Vloss = Iin * Rm
=======
Watts

Watts = V * Iin
Alternately P=I²R (P = I x I x Rm)
=======
Stalled Motor

Istall = Vin / Rm
=======
Torque constant

Torque constant: Kt=Kb x 1.345
Kb = Voltage constant (Volt/1000 RPM)
=======
Torque Loss

Torque = Kt * (Iin - Io)
=======
Termination

Wye = the number of winds you have performed
Delta = divide the number of turns by 1.73
=======
Watts per Horsepower

1 horsepower = 746 watts
=======

Acronyms
=======

Rm = Resistance value of the motor, derived from the guage of wire used

Pout = Power Out of the Motor expressed in Watts

Pin = Power In of the Motor expressed in Watts

Vin = Voltage Into the Motor

Iin = Current Into the Motor

Io = Noload Current of the Motor, derived from running a motor WOT without a prop at varying voltages. Io can be expressed with an associated Voltage and should be.

Kv = K value or voltage constant, the expressed value where the rpm can be surmised by a given voltage. For a 2000 Kv motor an input voltage of 10V would net 20000RPM.

Istall = The load current of a motor which is purposely stalled, hence not turning

Kt = Torque constant (oz-In/A)

Kb = Voltage constant (Volt/1000 RPM)

Note: Data has been gathered and utilized from various sources such as the aveox site as well as others.

 #2 Ron van Sommeren Oct 25, 2006 05:57 PM

Not exactly formulas:
Doubling the number of winds halves Kv (rpm/volt) and doubles Kt (torque/Ampere)
Doubling statorheight halves Kv, doubles Kt and (roughly) doubles maximum power.

 #3 tomekr Apr 13, 2007 01:28 PM

Max power (with akceptable efficiency) of the motor is about
Pin[W]=1600*Vmagnet[inch^3]
Pin[W]=0.1*Vmagnet[mm^3]
This formula is based on practice, and work well on neodym magnet. It is very usefull to calculate an appropriate max. supply voltage, rpm, proppeler etc. (based on the motor resistance and expecting efficiency or simply optimal motor current)

 #4 Fourdan May 12, 2007 05:17 PM

Kv ratio = 1.732 is a controversy
A lot of testers found a ratio between 1.78 and 1.9
Louis

 #5 marc780 Sep 20, 2007 04:05 PM

huh?

 #6 flyman77 Sep 29, 2007 08:12 AM

magnets and poles

How does one calculate how many magnets to use against the number of poles, and what decides the winding direction? Anyone please?
Thanks Brian

 #7 heliovaitsman Oct 26, 2007 12:47 PM

Squematic Circuit Z3007-26 HypÉrion

PLEASE SOMEBODY HAVE AN ELECTRIC CIRCUIT OF ELECTRIC MOTOR BRUSHLESS 12 POLES 14 MAGNETOS? THE MOTOR IS Z3007-26 HYPERION
the bindings betweem wires are delta or star?
TKS
Hélio Vaitsman

 #8 Spiritosl Oct 28, 2007 09:41 AM

Poles and magnets

Quote:
 Originally Posted by flyman77 How does one calculate how many magnets to use against the number of poles, and what decides the winding direction? Anyone please? Thanks Brian
Brian and others,
try this one! I found it on a German site three years ago

http://www.rclineforum.de/forum/thre...did=60302&sid=

Copy the program below (in dark red starting with <HTML> and ends with </HTML>) in Notes and save it as Poles and magnets.html and run it as a Java program.

<html>
<title>Schematic for electric motor windings</title>
<style type="text/css">
<!--
body { font-family: arial; font-size: 14px}
td { font-family: arial; font-size: 14px}
.result { background-color: #d0c0c0 }
-->
</style>

<script language="JavaScript">
<!--

function SymError()
{
return true;
}

window.onerror = SymError;

var SymRealWinOpen = window.open;

function SymWinOpen(url, name, attributes)
{
return (new Object());
}

window.open = SymWinOpen;

//-->
</script>

<script language="JavaScript">

// Lizenz:
// Verwendung und/oder Modifikation für eigene Homepage
// nur mit folgendem Verweis auf das Original:
// http://www.maltemedia.de/brushless/wicklungsschema/
// (C) 2004 overclocker_2001 alias oc2k1 & DrM (drmalte@maltemedia.de)
//
// Modifikation nur mit dem Einverständnis, daß die Modifikationen
// auch in das Original eingebaut werden dürfen.

function init()
{
document.Windungsrechner.Nuten.focus();
document.Windungsrechner.Nuten.value = "";
document.Windungsrechner.Pole.value = "";
document.Windungsrechner.Ergebnis.value = "";
}

function berechnen( form )
{
Nuten = eval( form.Nuten.value );
Pole = eval( form.Pole.value );

if( Nuten % 3 != 0 || Nuten < 3 ) {
document.Windungsrechner.Ergebnis.value = "Pole number must be divisable with 3!";
document.Windungsrechner.Nuten.focus();
document.Windungsrechner.Nuten.select();

return;
}

if( Pole % 2 != 0 || Pole < 2 ) {
document.Windungsrechner.Ergebnis.value = "Magnet number must be an even number!";
document.Windungsrechner.Pole.focus();
document.Windungsrechner.Pole.select();

return;
}

if( Pole == Nuten ) {
document.Windungsrechner.Ergebnis.value = "Pole number must be different from magnet number!";
document.Windungsrechner.Pole.focus();
document.Windungsrechner.Pole.select();

return;
}

Winkel = 180 * Pole / Nuten;
a = 0; b = 0; c = 0;
A = 0; B = 0; C = 0;
schema = ""
summe = 0;

for( i = 0; i < Nuten; i++ ){

if( summe >= 330 || summe < 30 ) {
schema += "A";
A++;
}

if( summe >= 30 && summe < 90 ) {
schema += "b";
b++;
}

if( summe >= 90 && summe < 150 ) {
schema += "C";
C++;
}

if( summe >= 150 && summe < 210 ) {
schema += "a";
a++;
}

if( summe >= 210 && summe < 270 ) {
schema += "B";
B++;
}

if( summe >= 270 && summe < 330 ) {
schema += "c";
c++;
}

summe = ( summe + Winkel ) % 360;
}

if( a == b && a == c && A == B && A == C ) {

while( schema.charAt(schema.length-1) == 'a' || schema.charAt(schema.length-1) == 'A' ) {
schema = schema.charAt(schema.length-1) + schema.slice( 0, -1 );
}

if( schema.charAt( 0 ) == "a" ) {
schema = schema.replace( /a/g, 'x' );
schema = schema.replace( /b/g, 'y' );
schema = schema.replace( /c/g, 'z' );
schema = schema.replace( /A/g, 'a' );
schema = schema.replace( /B/g, 'b' );
schema = schema.replace( /C/g, 'c' );
schema = schema.replace( /x/g, 'A' );
schema = schema.replace( /y/g, 'B' );
schema = schema.replace( /z/g, 'C' );
}

if( schema.search( /[bB]/ ) > schema.search( /[cC]/ ) ) {
schema = schema.replace( /b/g, 'x' );
schema = schema.replace( /c/g, 'y' );
schema = schema.replace( /x/g, 'c' );
schema = schema.replace( /y/g, 'b' );
schema = schema.replace( /B/g, 'x' );
schema = schema.replace( /C/g, 'y' );
schema = schema.replace( /x/g, 'C' );
schema = schema.replace( /y/g, 'B' );
}

document.Windungsrechner.Ergebnis.value = schema;

} else {
document.Windungsrechner.Ergebnis.value = "Invalid combination! ("+schema+")";
}
}

</script>

<body bgcolor=white onload="var SymTmpWinOpen = window.open; window.open = SymWinOpen; init(); window.open = SymTmpWinOpen;">
<form name="Windungsrechner">

<BR><BR>
<div align="center"><center>
<!-- <B>Scrift is still working, please be patient ;)</B><BR> -->
<B>Motor winding schema V1.0</B><BR><BR>
Dial in pole and magnet numbers and press = or press ENTER.
<BR><BR>
<tr>
<td>Poler:</td>
<td><input type="text" size="3" name="Nuten" maxlength="3"></td>
<td>Magneter:</td>
<td><input type="text" size="3" maxlength="3" name="Pole"></td>
<td><input type="submit" name="Berechnen" value="=" onclick="berechnen(this.form);return false;"></td>
<td><input type="text" size="64" name="Ergebnis" readonly class=result></td>
</tr>
</table>
<BR>
<!--
Number of poles must be a multiple of 3 and the number of magnet must be amuliple of 2.<BR>
Valid answers are given if there are equal numbers of A/a, B/b and C/c. 12P18M or 15P12M do not work.
-->
<BR><BR>
<BR> (C) 2004 overclocker_2001 alias oc2k1 & DrM (drmalte@maltemedia.de)</A>
<BR>Translated from German into English by Björn Hammarskjöld, Mora, Sweden, 2007
</center>
</div>
</form>
<p></p>
<noscript>
</noscript>

<a href="http://www.maltemedia.de/brushless/wicklungsschema/source.txt">Source</a>

</body>

<script language="JavaScript">
<!--

window.open = SymRealWinOpen;

//-->
</script>

</html>

 #9 Ron van Sommeren Oct 28, 2007 10:35 AM

Quote:
 Originally Posted by flyman77 How does one calculate how many magnets to use against the number of poles, and what decides the winding direction? Anyone please? Thanks Brian
Excellent motor building articles by Brian Mulder, a must read, will prevent you from asking a lot of questions you even did not know you were going to ask ;) ;)
http://www.southernsoaringclub.org.za/
-> Articles by SouthEasterners.
-> Electric Motors - part 1-5
-> Table in chapter 3

Or www.powercroco.de
-> konstruktion
-> kombinationstabelle

Do-it-yourself motor homepages, manuals/tutorials, checks and tests in this motor builders tips and tricks thread. The checks and tests may save you from frying your controller or motor. Thread is active, bookmark it for future reference and subscribe to it:

Vriendelijke groeten ;) Ron van Sommeren
diy brushless motor discussion group
int.electric fly-in & diy outrunner meet, Nijmegen, the Netherlands

 #10 jimweda Dec 18, 2007 07:46 PM

Motor knowledge...

Quote:
 Originally Posted by Ron van Sommeren Not exactly formulas: Doubling the number of winds halves Kv (rpm/volt) and doubles Kt (torque/Ampere) Doubling statorheight halves Kv, doubles Kt and (roughly) doubles maximum power.
I've seen a few posts that you have made on forums regarding motors and you seem to know your stuff. I've only been in the RC arena for about 4 months now but this is my background. I learned to fly planes on a Stryker F-27C, went to Hanger 9 F-22 Raptor (Nitro, which I do not like now, prefer electric) and from that point I've been flying FunJets (3 with Mega 16/15/3 (3000kv) & Align 430XL (3770kv), Kyosho F-16 EDF and Phase 3 F-16 EDF. Here's my question. I've been told by a couple people that I could actually make my own motors which is why I am here, researching. You seem to be one of the guys to talk to. This is what I am trying to attempt. I want to take the last 3 planes mentioned and make them scream and would like your advise on how to make motors that will make these birds scream. I know its not as simple as that, but I was hoping you could point me in the right direction towards winding my own motors to suit my needs. Currently for the Phase 3 F-16 the fastest flyers seem to be running Typhoon 2W & 2W-20/23's with Wemo mini fans or Alfa 5 blade fans. Others motors are Little Screamer Jet Screamers and a new Monster Jet Screamer that hasn't been released yet. I was talking to the R&D guy who is putting it into a WM400 fan unit and they're talking about doing about 160 - 170 mph with that set up. Can I make motors that will help me reach at least 120 mph or more by either prop or fan unit? I would sincerely appreciate any information you might pass my way. Thank you in advance and I look forward to hearing from you and others in the forum.

Jim

 #11 Ron van Sommeren Dec 19, 2007 05:51 AM

I cannot help you with motor size, winding numbers etc. for your plane, for that you need input from people who have experience with those planes.

Excellent motor building articles by Brian Mulder, a must read:
http://www.southernsoaringclub.org.za/
-> Articles by SouthEasterners.
-> Electric Motors - part 1-5

Do-it-yourself motor homepages, manuals/tutorials, checks and tests in this motor builders tips and tricks thread. The checks and tests may save you from frying your controller or motor. Thread is active, bookmark it for future reference and subscribe to it:

Vriendelijke groeten ;) Ron van Sommeren
brushless motor building tips & tricks
diy brushless motor discussion group

 #12 jimweda Dec 19, 2007 04:27 PM

Thanks Ron

Quote:
I appreciate your honesty, quick response and links to resources that may get me where I want to go. Thanks again.

Jim

 #13 barney 69 Aug 10, 2008 11:13 PM

Quote:
 Originally Posted by fly_boy99 ======= Watts Watts = V * Iin Alternately P=I²R (P = I x I x Rm) =======
I presume that Watts = U² / R ......... and if U is /2 , R must be /4 ( for "Watt" stay the same value )

Hi , if i want to "convert" my BLM ( wich is 2S configured ) in a 1S configuration , is it the good way if i give it ( my BLM ) the 1/4 of the original 2S config resistance ?

If it is made with 0.5 Ohms , does i give it 0.125 Ohms ( 2S => 1S ) ?

--------

Thanks to try to understand my translation ;)

 #14 Ron van Sommeren Aug 11, 2008 12:37 PM

Motors are not resistors, they behave differently. You have to halve the number of winds. That will gave you the same rpm. No you have room for thicker wire, that's nice because motorcurrent has doubled.

 #15 barney 69 Aug 12, 2008 03:10 AM

Ok , thanks ........ the wire will give me a very low resistance but i must not "think to much" about the resistance .

I must "think only" about KV ( halve the number of turns and give the stator the "maximum of copper" , maximum thickness to the wire ) , and "to say to me" that the maximum thicker wire does not want to say bad efficiency for the motor .

It is true ???

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