N Scale Locos Pulling Power

Xrayvizhen Feb 8, 2021

  1. badlandnp

    badlandnp TrainBoard Member

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    A lot of railroads have operating rules requiring that there be a pair of units with a cab facing both directions. The crews don't have to sit facing backwards with the controls to their side in such a way as to be twisted around at the waist. It's ok to do that here and there for a few, but a few miles of steady pulling backwards like that, and your back gets twisted up.
     
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  2. MRLdave

    MRLdave TrainBoard Member

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    Another thing you can check is gauge...........my experience is that Bachmann track does not match most other brands (at least with the track I have). Their locos are gauged to Bachmann track. I've had to adjust every Bachmann loco I have to get them to run/pull properly. If only half your wheel is sitting on the rail, your traction goes down significantly. Might not be your problem, and your loco probably still won't pull like an O scale one, but it should help.
     
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  3. mtntrainman

    mtntrainman TrainBoard Supporter

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    I am confused. :confused:

    Belen Yard uses a single BNSF 1643(SD40-2) to pull/switch up to 1 mile long strings of cars.


    If you are talking a consist going cross country...I would hve to say no on a single loco pulling a mile long train.

    .
     
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  4. badlandnp

    badlandnp TrainBoard Member

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    Within the confines of yards, a single unit is common, But the crews prefer two cabs, one each way. And if they go out to service any industry outside the yard limits, BNSF here in MT requires two cabs.
     
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  5. Onizukachan

    Onizukachan TrainBoard Supporter

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    you bet, first time I ran my ac12 I had to take about 6 box cars out of the consist and get it down to about 18 cars. It couldn’t pull 24 on the flat and level, would just spin the drivers.

    still needs the traction tires replaced (comes with spare set) but I just don’t want to do it! I have bull frog snot and need to do both it and the GS4 one of these days.
     
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  6. Mo-Pac

    Mo-Pac TrainBoard Member

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    Yes, the square cube law is the ticket. Back in the day 1990's I had a pair of BN Kato E8/9's. Even at a train show the pair was pulling 100+ cars with no effort. My Intermountain's and Atlas's I would need to consist five to six locomotives or more with at least two DPU's two thirds the way back or on the end.
     
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  7. NorsemanJack

    NorsemanJack TrainBoard Member

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    This thread has reminded me (again) why I decided to now own only Kato locomotives. I get it that some modelers are very focused on modeling a specific road/era, which almost demands that they buy models of specific prototypes regardless of manufacturer. I like certain roads, but I also like to buy a variety of roads. I'm also partial to the pre 1970s passenger era, so that makes Kato work out very well for me. I would like to have some war bonnet FP45s for my Super Chief/El Cap, but I'm not interested in buying Athearn equipment. The SDP40s are first cousin cowl units, so that's when it's time to pull out the Amtrak Super Chief/El Cap sets. It wouldn't shock me to see Kato produce some FP45s at some point. I have more E units, F units and PA units than I can count, but the only hood units I currently have are those fantastic Kato DRGW SD45s. Isn't it about time for those to be released with some more road numbers? A four unit consist would be really cool. :cool:
     
  8. locomcf

    locomcf TrainBoard Member

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    Years ago I noticed that several of my seven SD-24 locos could (literally) pull only half the number of cars that some of the others could. The locos were all from the same production run and appeared identical, so it had me somewhat puzzled. Then I realised that the best pullers were also the locos I had bought first, and the most recent acquisitions were the worst.

    I suspected that the wheels on new locos might be more "slippery" (shiny?) than the wheels on the locos that had more miles, and over the next few weeks I ran the newer locos a LOT. Over time, the number of cars they could pull slowly increased, and now they all pull around the same number.
     
  9. ggnlars

    ggnlars TrainBoard Member

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    I have spent some time examining this issue. As others have indicated, there are a number of things that impact the pulling capacity. It has been well documented that engine weight is a big factor. The next biggest factor is the motor capacity. Recent focus on low current draw(power) for DCC and noise reduction has taken a toll on the motor capacity. Other factors of importance are wheel material, surface roughness( traction tires being the ultimate), and wheel diameter. The difference between a scale 42 in wheel and a scale 40 in wheel is 5% in pulling capacity. Not much by it self, but it all adds up.
    Another factor that is important is the number of drive axles, as it is with real trains. However with models, how well the wheels are held in a plane will impact this result. You can easily have a six wheel truck that only has three wheels that are carrying the load. The actual traction is derived from the wheel stress, the wheel surface area in contact and the surface coefficient due to the surface roughness. Six wheels are better than four and certainly three. This is where the balance comes in as others have indicated.
    I have posted my work on www.llxlocomotives.com
     
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  10. Moose2013

    Moose2013 TrainBoard Member

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    @ggnlars

    Where are you getting these terms & concepts such as "wheel stress" & "holding wheels in plane", and your ideas on relationships between these as well as wheel diameters, number of wheels, surface roughness, etc. and, pulling capacity? How do you justify comparisons to 1:1 locomotives when the mechanics at 1:1 scale are vastly different than in n scale?

    With all due respect, speaking as an engineer, what you have written in the context that you have written it makes no sense.
     
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  11. NtheBasement

    NtheBasement TrainBoard Member

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    I would be interested in a discussion about how one accurately measures draw strength in grams. How are all the variables controlled so that only the loco's capability is being measured? How does one attach a line to a loco without causing some kind of pull up, down, or to the side? How do you make sure the PWM is identical on every run? What do you do to clean the track and loco wheels before measuring? etc.
     
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  12. nscalestation

    nscalestation TrainBoard Supporter

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  13. ggnlars

    ggnlars TrainBoard Member

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    Moose2013
    There are several references that I can give. Do not try to apply the approximate point load theory that you learned in first year statics. All materials strain. The amount varies as indicated by Young’s modules. Yes the load levels are far different than a 1:1 scale. However the physics is not. The force transfer is through the contact area and the mechanism is the stress caused by the weight & torque on the wheel.
    As for wheel alignment, again there are references to truck designs that do a better job that the standard stick model engine truck. However they are complex and expensive.
    I and others have given up on measuring drawbar force on these models. I have tried several gauges and a weight pulley method. Neither of which would correlate with what the engine would pull in terms of a know set of cars. So my go to method today is the number of fixed weight cars that the engine will pull and the speed variance as the number of cars increases. The maximum number is pulled a a speed just above zero. This is really not very valuable. The more important result is what is the speed for a nominal train length.
     
    Last edited: Apr 6, 2021
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  14. Moose2013

    Moose2013 TrainBoard Member

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    @ggnlars

    Apologies are offered for the following pointless rant. Nothing personal. Just don't care to read statements that appear to mislead in areas that this moose has, surprising to many, some knowledge...

    To you, good sir, Moose says: Poppy-cock!

    For example, there is no significant elastic deformation at the 1:160 scale, so the calculation of maximum traction capability is relatively simple. Whereas, at 1:1 scale, elastic deformation is considerable, and changes the mechanics of the effective friction between the wheels and the rails and therefore the methods of estimating the maximum traction capability.

    Having multiple powered axles as opposed to a single powered axle on a 1:1 locomotive serves to mitigate the load-limited rails, bridges, etc., and -- with disease'els (read diesels) -- allows additional motors for powered axles, where the loads are relatively very high compared to the rails, bridges, etc. upon which they transverse.

    Whereas with 1:160 scale locomotives, it would not matter if the wheels were powered on a single axle or multiple axles, provided the load across the combined powered wheels were the same. Consider a steam locomotive with a single driver axle and say 25 tons on the driver versus a steam locomotive with two drivers with the same 25 ton weight distributed across both driver axles (i.e. 12.5 tons on each axle). In such a case, at 1:160 scale, the math is relative simple as you haven't local deformations. The calculated traction limit would be the same for a single axle as it would be for two axles, F = uW, where F is the calculated tracking limit, u = static coefficient of friction between the drivers and the rails, and W the total weight on the drivers; the contact area is immaterial to this calculation.

    Having blathered on, Moose will go away...
     
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  15. ggnlars

    ggnlars TrainBoard Member

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  16. sd90ns

    sd90ns TrainBoard Member

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    There may be a lot of factors that affect tractive effort on an N-Scale locomotive by but loosing apx. 15% of its weight between one version and the other it probably makes all those other factors involved negligible if not irrelevant.

    This I think was demonstrated when I swapped the truck assemblies, thus the wheels, between the two Gp's and nothing changed with regards to each locomotives tractive efforts.
     
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  17. Moose2013

    Moose2013 TrainBoard Member

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    Okay, so you googled some terms and key words, and attached links to them. They do not support your prior comments, nor do they help explain what on earth you were trying to prove.

    Stick model? Having developed finite element models for more than three decades, was curious as to what you were trying to say with "stick model trucks". If you are referring to FEM stick models used to predict load paths, deflections, strains or the system kinematics of railroad trucks, that could make sense, but it is hardly applicable to 1:160 railroad models. But if you were trying to explain your comment of "wheels in plane", well, you have this moose lost. Did you mean keeping all wheels on the rails? 1:1 scale has suspensions for that that are not remotely comparable to their 1:160 brethren.

    Oh, Moose could go on ... Yeah, Moose really needs to get a life ... Again, nothing personal, just a moose cringing at reading statements that this moose finds technically inaccurate and that may be misleading to those that do not posses the requisite education and professional experience to recognize as inaccurate.

    Okay, Moose will attempt to ban moose-self from this thread. Again, nothing personal...
     
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  18. ggnlars

    ggnlars TrainBoard Member

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    Yes, I guess it is time to walk away.
     
  19. Moose2013

    Moose2013 TrainBoard Member

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    Agreed... Although, might end up walking to the same pub. If that happens, then Moose will buy the beer.
     
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  20. mtntrainman

    mtntrainman TrainBoard Supporter

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    I bought mine off Amazon back in 2014....

    https://www.amazon.com/20g-40Kg-Dig...42141&sr=8-12&keywords=digital+handheld+scale


    I did a fun little pull test back in March 2014. Here is a link to that discussion...
    https://www.trainboard.com/highball/index.php?threads/t-h-e-r-r-reborn.64636/page-27

    In the end...all locomotives are different. Even those from same manufacturer same production run etc....etc...etc..

    My conclusion...

    Run your locomotive and add cars till it slips.
    Remove cars one by one till it doesnt slip !
    Enjoy your trains !!

    Life is to short....
    "Dont sweat the petty and dont pet the sweaty" :whistle:
     
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