P2K GP30 speed?

NW Modeling List nw-modeling-list at nwhs.org
Mon Jun 8 12:46:16 EDT 2009

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

Gary Rolih



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 <mailto:nw-modeling-list at nwhs.org> Modeling List

To: NW <mailto:nw-modeling-list at nwhs.org> 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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