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<B><FONT SIZE=4><P>Electric Motors <BR>
</B></FONT>Engineering Notes</P>
<P>Electric motors are selected on the basis of type, output power and armature resistance.<BR>
The three common types of micro propulsion motors are:</P>
<P>Ferrite can (Mabuchi M20 and N20)<BR>
Coreless pager (Didel and SuperSlicks)<BR>
Brushless (Mighty Midget and Gold Line)</P>
<P>A ferrite can motor, which uses carbon brushes, hard ferrite ceramic magnets and a laminated steel armature core is generally the least expensive choice, and can use ordinary electronic speed controllers (ESCs). </P>
<P>A coreless motor is lighter and more efficient, employs metal brushes, rare earth magnets and a high inductance armature, and needs an ESC with a high switching frequency (&gt;60kHz).</P>
<P>If the cost of the controller and motor is not a concern, or you don�t want to use a gear drive (assuming a suitable size motor is available for your application) brushless is the way to go.</P>
<P>The required power output of a motor depends on airplane gross weight, wing loading and type of flying.</P>
<TABLE BORDER CELLSPACING=1 BORDERCOLOR="#c0c0c0" CELLPADDING=2 WIDTH=223>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=32>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">motor</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=32>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">output </P>
<P ALIGN="CENTER">power (W)</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=32>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">thrust </P>
<P ALIGN="CENTER">(g)</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=32>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">number</P>
<P ALIGN="CENTER">of cells</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">MK06-4.5</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.62</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">15</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">M20-3.6</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.74</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">17</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">MK07-3.3</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.79</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">20</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">SupSl-3.3</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.79</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">20</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">N20-2.4</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.08</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">22</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">SupSl-2.3</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.11</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">25</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">M20-1.5</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.54</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">28</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">N20-1.2</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2.37</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">35</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">10-3-32Y</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2.93</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">40</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">N20-3.7</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.24</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">51</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">10-7-16</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">4.18</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">61</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13-4-15Y</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">8.12</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">104</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13-6-11Y</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">10.7</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">118</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13-4-15Y</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13.8</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">139</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3</FONT></TD>
</TR>
<TR><TD WIDTH="35%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13-6-11Y</FONT></TD>
<TD WIDTH="25%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">21.0</FONT></TD>
<TD WIDTH="19%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">179</FONT></TD>
<TD WIDTH="21%" VALIGN="MIDDLE" HEIGHT=17>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3</FONT></TD>
</TR>
</TABLE>

<P>Maximum thrust (in grams) is roughly equal to:<br>
M20 and N20: (100 x output power)<SUP>2/3</SUP><BR>
6 or 7mm pager: (106 x output power)<SUP>2/3</sup><BR>
Brushless: (119 x output power)<SUP>2/3</sup></P>
<P>For sedate flying and low wing loading, thrust equal to 1/3 to 1/2 of airplane gross takeoff weight works well. An approximate rule is to use one cell for systems that develop less than 40g of thrust, 2 cells for 40g to 120g, and 3 cells for anything over 120g.</P>
<B><P>Choosing the right prop &amp; gear ratio<br>
</B>The prop and gear ratio should be set so that at full throttle, the motor operates at maximum output power. If the motor can�t run at full power for at least 15 seconds (takeoff and climb out regime) without overheating or excessive wear, switch to a motor with a higher armature resistance, or (if you don�t mind sacrificing some power/weight) set the full throttle operating point closer to maximum efficiency by increasing the gear ratio or reducing the prop diameter.<br>
<P>The operating point of a motor may be determined either by measuring speed or current.</P>
<TABLE BORDER CELLSPACING=1 BORDERCOLOR="#c0c0c0" CELLPADDING=2 WIDTH=299>
<TR><TD WIDTH="22%" VALIGN="BOTTOM" ROWSPAN=2 BGCOLOR="#ffffff" HEIGHT=27>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">motor</FONT></TD>
<TD WIDTH="30%" VALIGN="MIDDLE" COLSPAN=2 BGCOLOR="#ffffff" HEIGHT=27>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">max power speed</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" ROWSPAN=2 BGCOLOR="#ffffff" HEIGHT=27>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">max power</P>
<P ALIGN="CENTER">current (A)</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 ROWSPAN=2 BGCOLOR="#ffffff" HEIGHT=27>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">voltage</P>
</FONT><FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">(V)</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=27>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">torque</FONT></TD>
</TR>
<TR><TD WIDTH="16%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=24>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">(rpm)</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=24>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">(rev/s)</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=24>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">(mN-m)</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">MK06-4.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">23519</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">392</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.41</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.253</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">M20-3.6</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">11437</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">191</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.51</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.614</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">MK07-3.3</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">14268</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">238</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.49</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.527</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">SupSl-3.3</FONT><FONT FACE="GreekC" SIZE=1>W</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">14268</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">238</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.49</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.527</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">N20-2.4</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">12298</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">205</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.77</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.839</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=1><P ALIGN="CENTER">SupSl-2.3</FONT><FONT FACE="GreekC" SIZE=1>W</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">17617</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">294</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.69</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.602</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">M20-1.5</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">23409</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">390</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.01</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.630</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">N20-1.2</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">16167</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">269</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.56</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.5</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.40</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">10-3-32Y</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">8643</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">144</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.03</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">7.0</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.23</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">N20-3.7</FONT><FONT FACE="GreekC" SIZE=2>W</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">18349</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">306</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.00</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">7.0</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.69</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">10-7-16</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">7747</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">129</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.43</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">7.0</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">5.16</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13-4-15Y</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">6848</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">114</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">0.60</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">7.0</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">11.3</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13-6-11Y</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">6966</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">116</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.42</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">7.0</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">14.6</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13-4-15Y</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">10009</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">167</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">3.23</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">10</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13.2</FONT></TD>
</TR>
<TR><TD WIDTH="22%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">13-6-11Y</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">9785</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">163</FONT></TD>
<TD WIDTH="14%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">4.67</FONT></TD>
<TD WIDTH="18%" VALIGN="MIDDLE" COLSPAN=2 HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">10</FONT></TD>
<TD WIDTH="16%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">20.5</FONT></TD>
</TR>
</TABLE>

<B><P>To calculate the gear ratio<br></B>
Gear ratio = (prop const. x motor speed<SUP>2</SUP> / motor torque)<SUP>1/3</P>
</SUP><FONT SIZE=2><P>[torque] = mN-m <BR>
[speed] = rev/s</P></FONT>
<TABLE BORDER CELLSPACING=1 BORDERCOLOR="#c0c0c0" CELLPADDING=2 WIDTH=140>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" BGCOLOR="#ffffff" HEIGHT=34>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">prop</FONT></TD>
<TD WIDTH="52%" VALIGN="TOP" BGCOLOR="#ffffff" HEIGHT=34>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">prop const.</P>
<P ALIGN="CENTER">(g-m<SUP>2</SUP>/rev<SUP>2</SUP>)</FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">U-80</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">6.40 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-5</SUP></FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">4025</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.22 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-4</SUP></FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">5030</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2.84 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-4</SUP></FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">5043</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">4.80 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-4</SUP></FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">6030</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">5.40 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-4</SUP></FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">6050</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">1.45 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-3</SUP></FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">WT20x10</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">2.91 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-3</SUP></FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">WT23x12</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">5.37 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-3</SUP></FONT></TD>
</TR>
<TR><TD WIDTH="48%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">WT25x12</FONT></TD>
<TD WIDTH="52%" VALIGN="MIDDLE" HEIGHT=16>
<FONT FACE="Arial" SIZE=2><P ALIGN="CENTER">8.90 </FONT><FONT FACE="Arial" SIZE=1>x10<SUP>-3</SUP></FONT></TD>
</TR>
</TABLE>

<P>Example gear ratio calculation: <br>
<B>N20-3.7<FONT FACE="GreekC">W</FONT> motor @ 7V<br></B>
Torque @ max power = 1.69mN-m<BR>
Max power speed = 306 rev/s</P>
<B><P>GWS 6050 prop constant<br>
</B>= .00145 g-m<SUP>2</SUP>/rev<SUP>2</P>
</SUP><P>Gear ratio = (.00145 x 306<SUP>2 </SUP>/1.69)<SUP>1/3 </SUP>= 4.3:1<br>
-----------------------------<br>
If torque @ max power is not given, <BR>
it can be calculated using this equation:<BR>
(power = <i>pi</i> x motor speed x torque/500)<BR>
Torque = 500 x power / <i>pi</i> x speed</P>
<P>Example motor torque calculation:<br>
<B>13-4-15Y motor @ 7V<br></B>
Max power = 8.12W<BR>
Speed @ max power = 114 rev/s<br>
Torque = 500 x 8.12W / 3.142 x 114 rev/s = 11.3 mN-m &nbsp;</P>
<B><P>To select a direct drive prop<br>
</B>The prop constant of a direct drive prop = motor torque / motor speed<SUP>2</P>
</SUP><P>Example direct drive prop calculation:<br>
<B>13-4-15Y motor @ 7V<br>
</B>Torque @ max power = 11.3 mN-m<BR>
Speed @ max power = 114 rev/s<br>
Prop constant = 11.3 / 114<SUP>2 </SUP>= 8.70 x 10<SUP>-4</SUP> g-m<SUP>2</SUP>/rev<SUP>2</SUP><br>
---------------------<br>
<b>Example prop constant calculation:</b><br>
The torque required to turn a prop is proportional to the square of prop speed:<br>
(torque = prop constant x speed<sup>2</sup>)<br>
Prop constant = torque/speed<sup>2</sup>

<p><b>GWS 6050 prop example</b><br>
7.31mN-m @ 71 rev/s<br>
Prop const. = 7.31/71<sup>2</sup> = .00145 mN-m-s<sup>2</sup>/rev<sup>2</sup><br>
 = .00145 g-m<sup>2</sup>/rev<sup>2</sup><br>
-----------------------------------------<br>
<b>Alternate Units</b> (power = speed x torque)<br>
[torque] = N-m<br> 
[speed] = rad/s</p>
<p>Example:<br><b>N20-3.7<FONT FACE="GreekC">W</FONT> motor</b> @ 7V<br>
max power speed = 1922 rad/s<br>
<b>GWS 6050 prop</b><br>
0.00731 N-m @ 446 rad/s<br>
prop constant= .00731/446<sup>2</sup> = 3.67 x 10<sup>-8</sup> N-m-s<sup>2</sup><br>
= 3.67 x 10<sup>-8</sup> kg-m<sup>2</sup></p>
<p>Gear ratio = 4.3:1<br> 
(3.67 x 10<sup>-8</sup> x 1922<sup>2</sup> /.00169)<sup>1/3</sup><br>
------------------------------------------<br>
<b>Common Pitfalls</b><br>
The efficiency and power output of a 2-cell motor<br>
operating on one cell will be low compared to motor weight.</p>
<p>The thrust produced by a 1-cell motor operating on two cells<br>
without overheating will be low.</p>
<p>If a motor draws more than the maximum power current,<br>
thrust will decrease while input power will increase.</p>
<p>The power output of a motor will decrease if it runs<br> 
faster than the maximum power speed.</p>
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@ Telegram