N Scale Locos Pulling Power

Xrayvizhen Feb 8, 2021

  1. Mo-Pac

    Mo-Pac TrainBoard Member

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    I will like to hear more about the physics involved with the 1:1 locomotives that you started to discuss. As for as 1:160 it is very hard to make sense of the physics involved in it.


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  2. Doug Gosha

    Doug Gosha TrainBoard Member

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    Don't you guys ever want to just watch trains run without getting all "scientific"?

    :D

    Doug
     
  3. ggnlars

    ggnlars TrainBoard Member

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    Sure, but the OP was about N scale locos pulling power. The answer will involve some level of discussion of the laws of physics that apply to running our trains. The simple answer is add more weight, but in a lot of cases the nanufacturer has do that. However the model does not do as well as other lighter models. To understand the why and what can be done now requires more understanding of the problem.
     
    Last edited: Apr 8, 2021
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  4. Moose2013

    Moose2013 TrainBoard Member

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    Yes! Always! :)

    And Moose is not going to attempt to explain the science behind 1:1 traction capability analysis...

    @Mo-Pac

    Moose’s professional engineering experience is primarily concerned with the design and structural analysis of aircraft structure and some mechanical systems. Railroad engineering, including wheel/rail mechanics and analysis, is not Moose’s forte by any means. The mechanics and analysis of said railroad systems are relatively complex, and they are dissimilar to the bearing/wing structure contact systems with which Moose has experience, so unfortunately for you and everyone else here (including Moose), the grand railroad wheel/rail evaluation 101 course that you, eh-hem, hoped for, will not be offered... Sorry!

    Please understand that another member here appeared to be asserting that the underlying mechanics and thus the analysis of locomotive pulling capability was comparable between 1:160 models and 1:1 real world machines. There are significant differences between their respective materials, designs, manufacturing requirements & constraints, loads, suspensions, etc., and the micro-structure of associated materials, lubricants and contaminants do not change with scale, therefore they are not comparable. An experienced engineer would recognize their differences and approach the analysis of each as applicable to those underlying attributes that make them different.

    When Moose first found this thread -- true to the heart of an engineer -- Moose wondered what the mechanics of 1:1 wheel/rail contact might be and how it might be evaluated. Moose searched for industry papers on the subject as Moose’s normal go-to reference materials (Roark, Bruhn, aircraft company design manuals and publications) would likely be of little use (and were not handy!). Moose found an FRA publication on the subject of wheel/rail friction, which seemed a good start! Honestly, reviewing this document – and not getting paid to do so – was enough effort expended on this subject for this poor moose’s brain. Moose concluded it wasn’t worth exploring further since Moose had modeling to do!

    Moose attached copy of this paper for your perusal.
     

    Attached Files:

    Last edited: Apr 8, 2021
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  5. DCESharkman

    DCESharkman TrainBoard Member

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    As a Physicist, Engineer and Mathematician, there are more variables than wheel-rail friction. There is wind shear being the prevailing winds in the locale, plus the air friction of the whole train and many more. Only the air friction of the whole train applies here. There is also the fiction of the wheels, all the wheels to be considered as well. This is not to mention the changes in rail temperature versus the wheel temperature. We could also get int to wheel bearing lubrication levels and types, wheels out of round etc.

    But all this is just jabberwocky!

    Trying to make the actual comparisons is just silly. All or in most cases our cars have no internal mass to compare to prototype the loads.

    A 60 ton railcar is 750 scale pounds in N-Scale. I have no idea how many locomotives it would take to pull that and are we sure the track can hold that weight? What would be the scale weight of 100 cars?

    The whole of the locomotive pulling power is not in the weight of the frame as much as it is in the torque of the motor. The problem with using Atlas as an example is the it was not the weight removal that lessened the pulling power, it was the reduced torque of the scale speed motors. It is the Torque that starts the movement and if that is less than it used to be, it is more likely the motor is the predominant cause. I am not say that a little of the loss was not due to reduced frame weight, it is a very minor contributor.

    So there is no real science that can be modeled correctly, so we should not be trying to compare the two. That is unless you are pulling scale weight cars!
     
  6. ggnlars

    ggnlars TrainBoard Member

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    As the paper says “Vehicle/track interaction is governed by four main factors: metallurgy, contact mechanics, suspension characteristics, and friction”. This is the same for a locomotive of any size. The individual part duty cycle & life requirements are different, which requires different geometry solutions.
    The fundamental physics of power transmission from wheel to track is the same.
     
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  7. ggnlars

    ggnlars TrainBoard Member

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    Weight scales with volume not linearly.
    My experience would indicate that car would weigh around 6 ounces in N scale size. The actual cars weigh around 0.6 ounces, but they are not fully loaded. See: http://www.llxlocomotives.com/?p=2718
     
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  8. Moose2013

    Moose2013 TrainBoard Member

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    :eek:

    And following your thoughtful post, hopefully everyone is back to running trains... :)

    Side note: IMHO (in Moose's humble opinion), the conclusion at which @mtntrainman arrived is the most practical answer for determining an n scale locomotives pulling power.
     
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  9. sd90ns

    sd90ns TrainBoard Member

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    Don't forget to clean the "Bearing cups" those dimpled bits of brass that transfers the current from the axle points to that pickup strip.
    An incredible amount of gunk builds up in those cups in a very short period of time.


    I had an old Life Like F Something-or-other that could haul till it stalled.
     
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  10. Doug Gosha

    Doug Gosha TrainBoard Member

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    And don't forget, if the guy next door decides to eat Cheerios instead of Wheaties, one day, and a blade of grass becomes detached in the lawn and blows away and somebody in town rotates his tires, it will affect the pulling power of your locomotives.

    Doug
     
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  11. tehachapifan

    tehachapifan TrainBoard Member

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    I keep seeing replies that seem to imply that an N scale car or loco, if weighted correctly, would be hundreds of (real) pounds. A buddy of mine used to proclaim the same thing. This can't possibly be right. Imagine if we were scaled-up to 160 times our actual size. I'm pretty sure we could lift a 1:1 car or loco if we were almost a thousand feet tall, but we shouldn't be able to lift (or barely be able to lift) an N scale car at our actual size? I don't think, as others have indicated, that weight scales the same way size does. There's other factor(s) in play. Mass, I believe?
     
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  12. Moose2013

    Moose2013 TrainBoard Member

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    @tehachapifan

    Hmmm, 1/160 × 60 tons = 750 lbs-force which assumes a linear relationship, but should be based on volume, therefore 1/160^3 × 60 tons = 0.03 lbs-force.
     
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  13. tehachapifan

    tehachapifan TrainBoard Member

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    I'm so not a mathematician or physicist that I don't know if what you posted is in support of or contradicts what I said.:p
     
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  14. Moose2013

    Moose2013 TrainBoard Member

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  15. tehachapifan

    tehachapifan TrainBoard Member

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    OK, so you're in the camp that says an N scale freight car should weigh over a hundred pounds? Am I not picking up on sarcasm or getting a joke? Not good at that in the real world and terrible at it in written form.
     
  16. Moose2013

    Moose2013 TrainBoard Member

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    Not sure what you mean. If a 1:1 freight car weighs 60 tons, then the 1:160 scale equivalent would be 0.03 lbs as previously noted. Sadly, no sarcasm or jokes there. Now, of course, what the recommended weight of an n scale car should be for optimal performance on your layout is another thing, AND this moose is not going to get into that debate. :eek:
     
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  17. tehachapifan

    tehachapifan TrainBoard Member

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    Ok, I think we're actually on the same page as far as what an N scale freight car should way then. It's not 60 tons divided by 160. So, what did I say that's not correct then?
     
  18. nssd70m2

    nssd70m2 TrainBoard Member

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    Weight is a three dimensional equation, so 1:1 coal car to 1:160 n scale coal car is:

    286,000 lbs. gross weight (of modern rail car) times 16 ounces (in a pound) equals 4,576,000 ounces divided by 160 cubed or 4,096,000 (width x height x length) equals

    1.1171875 ounces or 31.672265625 grams
     
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  19. Moose2013

    Moose2013 TrainBoard Member

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    What @nssd70m2 said ... The thing that people seem to miss is that the weight of an object is a function of its length, width and height.
     
    Last edited: Apr 8, 2021
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  20. gcav17

    gcav17 TrainBoard Member

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    See now that make sense sorta. Try to get an engineering guy to speak English and in layman's terms is next to impossible.

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