P2K GP30 speed?

[NW Modeling List]

Hi Gary; 



Your note seems to indicate that you are assuming the motor is perfect.  There are also variations motor to motor such as: 



    • the variability of the steel in the laminations 
    • the number of laminations - being off ±1 is not uncommon on low end end motors due to thickness variation of the lamination material. 
    • 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. 
    • geometric variability in the magnets. 



For low end motors like in our model locomotives, three sigma limits of ±10% within a particular model of motor should be expected. 



I worked on spindle motors and voice coil motors in hard disk drives. 



Nigel 

http://www.linkedin.com/in/nigelmisso 


----- Original Message ----- 
From: "NW Modeling List" <nw-modeling-list at nwhs.org> 
To: "NW Modeling List" <nw-modeling-list at nwhs.org> 
Sent: Monday, June 8, 2009 9:46:16 AM GMT -08:00 US/Canada Pacific 
Subject: RE: P2K GP30 speed? 



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. 



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?). 



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. 



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. 



Gary Rolih 

Cincinnati  








From: nw-modeling-list-bounces at nwhs.org [mailto:nw-modeling-list-bounces at nwhs.org] On Behalf Of NW Modeling List 
Sent: Sunday, June 07, 2009 6:10 PM 
To: NW Modeling List 
Subject: Re: P2K GP30 speed? 




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. 





Dick Dunford 


Blacksburg VA 




----- Original Message ----- 


From: NW Modeling List 


To: NW Modeling 


Sent: Friday, June 05, 2009 7:55 PM 


Subject: P2K GP30 speed? 




Hi Listers, 



            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? 



Thanks in advance, 

John Hecker 



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