<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: Arial; font-size: 12pt; color: #000000'><P>Hi Gary;</P>
<P> </P>
<P>Your note seems to indicate that you are assuming the motor is perfect. There are also variations motor to motor such as:</P>
<P> </P>
<UL>
<LI>the variability of the steel in the laminations </LI>
<LI>the number of laminations - being off ±1 is not uncommon on low end end motors due to thickness variation of the lamination material.</LI>
<LI>variability in the magnet material - high energy NdFeB magnets are typically ±5%; cheaper ferrite magnets can be "tuned" resulting in tighter tolerances, but less efficient motors.</LI>
<LI>geometric variability in the magnets.</LI></UL>
<P>For low end motors like in our model locomotives, three sigma limits of ±10% within a particular model of motor should be expected.</P>
<P> </P>
<P>I worked on spindle motors and voice coil motors in hard disk drives.</P>
<P> </P>
<P>Nigel</P>
<P><A href="http://www.linkedin.com/in/nigelmisso">http://www.linkedin.com/in/nigelmisso</A></P>
<P><BR>----- Original Message -----<BR>From: "NW Modeling List" <nw-modeling-list@nwhs.org><BR>To: "NW Modeling List" <nw-modeling-list@nwhs.org><BR>Sent: Monday, June 8, 2009 9:46:16 AM GMT -08:00 US/Canada Pacific<BR>Subject: RE: P2K GP30 speed?<BR><BR></P>
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<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Remember that a DC motor has a straight line output curve on a horsepower diagram. For a given RPM there is a fixed torque output at a certain voltage. ( Horsepower equals torque times rpm.) Basically at zero RPM you have very high torque and at max rpm you have virtually no torque. To change this curve- really the slope of the straight line, the internal windings have to be changed. Gearing is a way to match the motor output to the load, in other words, change the torque output at the gearbox output. Thus, the slower locomotive with the higher gear ratio should be able to pull more cars assuming that the wheel adhesion does not come into play. Speed control via gearing change is not really the right way to look at the issue. Output torque is.</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">For two models of the same production batch to run differently, there are some ‘quality’ issues within one of the models that increases its frictional losses as compared to the other model. It could be alignment of shafts, binding somewhere in the mechanism, brush to commutator issues, friction or binding within the trucks or wheel sets (is the wheel spacing correct?). </SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">The point of all of this is that when one observes a change between two models one needs to compare the gear ratios and also see if the motor was changed to determine what might be done to correct the issue.</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Digital controls pulse the voltage to the motor (Pulse width modulation) via the semiconductors to bring the dissimilar models into similar speeds, which makes the motor not run on the straight line curve, but to one side of the curve.</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Gary Rolih</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Cincinnati </SPAN></FONT></P>
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<P class=MsoNormal><B><FONT face=Tahoma size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Tahoma">From:</SPAN></FONT></B><FONT face=Tahoma size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma"> nw-modeling-list-bounces@nwhs.org [mailto:nw-modeling-list-bounces@nwhs.org] <B><SPAN style="FONT-WEIGHT: bold">On Behalf Of </SPAN></B>NW Modeling List<BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Sunday, June 07, 2009 6:10 PM<BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> NW Modeling List<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> Re: P2K GP30 speed?</SPAN></FONT></P></DIV>
<P class=MsoNormal><FONT face="Times New Roman" size=3><SPAN style="FONT-SIZE: 12pt"></SPAN></FONT> </P>
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<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">It has been my experience that in many cases two identical locomotives from the same run often operate at different speeds. Not using DCC, my solution has always been to put the faster locomotive behind the slower. That way the faster one is slowed down by doing most of the pulling of the train.</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Dick Dunford</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Blacksburg</SPAN></FONT><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> VA</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">----- Original Message ----- </SPAN></FONT></P></DIV>
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<P class=MsoNormal style="BACKGROUND: #e4e4e4"><B><FONT face=Arial size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Arial">From:</SPAN></FONT></B><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> <A title=nw-modeling-list@nwhs.org href="mailto:nw-modeling-list@nwhs.org" target=_blank>NW Modeling List</A> </SPAN></FONT></P></DIV>
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<P class=MsoNormal><B><FONT face=Arial size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Arial">To:</SPAN></FONT></B><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> <A title=nw-modeling-list@nwhs.org href="mailto:nw-modeling-list@nwhs.org" target=_blank>NW Modeling</A> </SPAN></FONT></P></DIV>
<DIV>
<P class=MsoNormal><B><FONT face=Arial size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Arial">Sent:</SPAN></FONT></B><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> Friday, June 05, 2009 7:55 PM</SPAN></FONT></P></DIV>
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<P class=MsoNormal><B><FONT face=Arial size=2><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Arial">Subject:</SPAN></FONT></B><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> P2K GP30 speed?</SPAN></FONT></P></DIV>
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<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Hi Listers,</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"> I was able to run some new engines on a friend’s layout this afternoon. For the first time I ran my new Athearn N&W SD45’s. They ran great! I tried a new N&W P2K GP30 and the 45’s just dragged it along. It appears to run about half speed of the Athearn's. I didn’t have any of my older Athearn's or PPW or Atlas to compare it to. So my question is that the P2K’s will only run with other P2K’s?</SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial"></SPAN></FONT> </P>
<P class=MsoNormal><FONT face=Arial size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Thanks in advance,</SPAN></FONT></P>
<P class=MsoNormal><B><I><FONT face=Arial size=3><SPAN style="FONT-WEIGHT: bold; FONT-SIZE: 12pt; FONT-STYLE: italic; FONT-FAMILY: Arial">John Hecker</SPAN></FONT></I></B><FONT face=Arial><SPAN style="FONT-FAMILY: Arial"> </SPAN></FONT></P>
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