N Scale Locos Pulling Power

Xrayvizhen Feb 8, 2021

  1. Inkaneer

    Inkaneer TrainBoard Member

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    The LifeLike FA/B1's were no slouches thin the traction dept. either.
     
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  2. Point353

    Point353 TrainBoard Member

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    The black finish that manufacturers are applying to loco wheels can be relatively slippery until it wears off the treads.

    The need to carve space out of the metal loco frames in order to accommodate the DCC electronics (and speaker, if equipped with sound) has left the locos significantly lighter than in the DC-only days and, thus, with less pulling power. Running multiple units is a solution to that issue.

    The prototype SD45 was of the first locos to incorporate a wheel-slip control system to improve traction.
    However, some railroads, that in the past had assigned four F or GP units to a train over a particular route, might have had a rule that any train must have at least 16 powered axles worth of locomotives. While a pair of six-axle SD45s would have been able to adequately power the train, the minimum 16-axle rule would find a single extra F or GP unit added to the consist. The downside was that, if the gradient and/or weather conditions made the F/GP unit slip, it couldn't regain traction as quickly as the SD45s and would end up being deadweight. Then the train would tend to bog down or, worst case, stall out.
     
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  3. Massey

    Massey TrainBoard Member

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    My test noted above was on my small 2 loop layout, and it was flat. I didn’t even get the SD40-2 into a curve. The pulling of the empire builder was on a modular layout (no grades) at a show, I was getting the cars out of the way of another train, and my GP40 was the closest thing I had. My 2 P42s were not even on the rails yet.
     
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  4. NtheBasement

    NtheBasement TrainBoard Member

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    When I converted my old locos to DCC I got the frames milled and my mine job SD40 went from pulling 21 cars up grade to 17 due to the weight loss. So if you want pulling power, get an old DC loco thats full of metal and isn't even DCC ready.

    If you add weight, concentrate on the front half of the loco. There is less metal on the front truck than the rear so the front slips first. Once the front slips there is a cascade. Slipping wheels have less traction, so the back truck has to do more work with only half the wheels - instant slippage. It follows that putting weight behind the back bolster is counterproductive because it levers weight off the front truck, causing it to slip more easily.
     
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  5. Xrayvizhen

    Xrayvizhen TrainBoard Member

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    Thanks guys. The wheels can't be dirty since the loco is new, the incline is on a straight section of track and I haven't noticed any kind of finish on the wheels that could be causing the slippage, but I'll check.
    Adding weight sounds like the easiest solution - that is, if it works. I'll experiment first with some lead weights that I'll just tape to the loco and see if that helps and it it does will find some tungsten putty.
     
  6. Massey

    Massey TrainBoard Member

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    So, I pulled out my Inter Mountain SD40-2 tonight and put a few of my Micro Trains planet cars behind it. It pulled the Sun and Inner planets just fine, so I added Jupiter and Neowise, and that’s when it started to struggle. So off they went and as the train did a few laps around my T-Trak modules, it started picking up speed without throttle changes. So I added Jupiter and Neowise back and it was pulling them just like the other 5 cars. So 7 cars for another hour or so, and the loco seemed to move them pretty ok. It pushed better than pulled but still it was not slipping. I added the rest of the cars, and that left me with a 11 car train, and a loop of track.

    This worked well for a while, the locomotive started gaining speed, then after a while it started slowing down. All while not touching the throttle, Running DC, then it stopped. The throttle was about 3/4 from full, but the loco was going pretty slow the entire time.

    The shell was pretty warm over where the motor is, so I called it a night for this locomotive. I’m thinking a few more hours with 5 or 6 cars will help it’s performance out even more. Right now I have the entire planet set (except the last 4 extras) running with a SD70ACe locomotive, and my Hello Kitty Shinkansen running on my modules.
     
  7. BNSF FAN

    BNSF FAN TrainBoard Supporter

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    That is cool Massey! Interesting how that loco sped up and then slowed down as time passed.

    Hopefully my Neptune car is on it's way as well. This has turned out to be a really great collection of cars. I have one set on the layout and have pulled them with a pair of Atlas SD60's with no sign of struggle. I'm thinking they will pull the entire set once all are out with no problem. Of course, they are DC and fairly heavy and have always been good pullers.
     
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  8. Massey

    Massey TrainBoard Member

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    I am pulling the entire 11 car set right now with one Kato SD70ACe loco and it’s pulling them with no struggle. I only have 2 lighted cars in my set so there that too. Not sure how it would pull a full set of lighted cars, they are quite a bit heavier.
     
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  9. NorsemanJack

    NorsemanJack TrainBoard Member

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    Are you saying that an IMR SD40-2 can only pull four cars?! I must be confused.
     
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  10. Massey

    Massey TrainBoard Member

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    It eventually would pull all 11 cars, but my throttle was about up about 3/4 from full and the train was only rolling at yard speed. At full throttle it would pull about the same as my Kato SD70ACe at 1/4 throttle. This engine has never been a good puller, wheel slip is really common on it. When I had 7 of my planet cars (the Sun being the only lighted one at the time) the wheels would slip, and the train wouldn’t pull the cars at all. I took 2 off then tried again, it pulled 5 just fine. I let it go that way for a bit over an hour, then added 2 more cars again and it pulled them fine... slow but fine. Another hour passed and I put all 10 of my planet cars on and it would pull them but didn’t have much of a top speed.

    I don’t know if there was something like oil or whatnot on the wheels, but it couldn’t pull well at first. Also the longer I ran it the faster it got, so I’m guessing this engine is still breaking in. I bought it at a show and the vender had it in the “new” part of his collection, so I am assuming it was never run, or only test run before I got it. When I tried to run it back when I first got it home, it would not pull 5 Kato Metra Bi-Levels with metal wheels, it just sat there spinning the wheels.
     
  11. sd90ns

    sd90ns TrainBoard Member

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    The pulling power of our N-Scale locomotives is primarily dependent on weight. Some will say that the composition of the locomotives wheels has some to do with tractive effort, more about that later.

    Here I will perform a comparison of two Atlas Gp7/9's, one is an oldie from the first batch of locos Atlas produced after they cut loose from Kato, strictly DC operations.
    The other is a later model that is designed from the ground-up for the inclusion of DCC.
    [​IMG]

    On the left is the newer model, on the right is the old model.

    [​IMG]

    Now with the shells off. Again, the one on the left is the newer model. Note the significant amount of frame material that has been removed so as to make room for the large PC Board necessary for DCC operation.
    Now for a close-up.
    [​IMG]
    Old frame.
    [​IMG]
    New frame.

    From the top.
    [​IMG]
    Old frame.

    [​IMG]
    New frame.
    That is a lot of missing material and that's not all. If you were to open these up you would notice that the hollow space inside where the motor is located is larger on the new frame than on the old. This is to allow for the little plastic motor holder that isolates the motor from the frame and is required for DCC operation.

    To make a long story short, I know, too late for that, the old loco weighs in at 68.3 grams while the newer model weighs 58.2 grams a difference of 10.1 grams or a loss of 14.79%.

    How does this workout in tractive effort.
    Glad you asked!

    On my layout is a switchback with a 4% grade beginning from a dead stop.
    The old Gp7/9 will push four Model Die Cast mechanical reefers up that incline without stalling.
    The newer Gp7/9 only manages three.
    Now for the wheel aspect I mentioned earlier. Some people seem to think that there was a change in the material used in the manufacture of our locomotives wheels, Atlas in particular, with newer wheels being slipperier then the older model wheels.
    Well as an experiment I switched out the truck assemblies between those two Gp's and nothing changed with regards to tractive effort.
    The old Gp with the newer trucks pulled the same four cars while the new Gp with the old trucks still only managed three.
    Wheel difference didn't seem to make any difference, it's all in the weight.
     
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  12. MK

    MK TrainBoard Member

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    Excellent analysis sd90ns. And what until you get a LATEST model with sound. Then Atlas hollows out the fuel tank for the speaker. Most weight loss! :whistle: I know that's the nature of the beast if you want sound. Just buy two of the same loco. :LOL:
     
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  13. mmagliaro

    mmagliaro TrainBoard Member

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    Adding weight is the first thing I would try.
    But one thing I would say "no" to is tungsten putty. I know people like to use it because it is formable and it can be "packed in" anywhere, but being in putty form means a lot of it isn't actually tungsten. It reduces the density so much that you would be better off with lead. Tungsten putty is typically around 10g/cc. Pure tungsten is about 19. So you need to pack in almost twice as much putty compared to just solid tungsten to get the same weight. My suggestion would be to scour the internet for tungsten cubes, disks, or plates in various sizes that you can stick into any available cavity, just held in place by a dab of rubbery cement like Walthers Goo. Good places to look are the online Pinewood Derby supply stores, which often sell bags of really tiny disks that can be slipped in anywhere. You can also find some online industrial suppliers that will sell you little cubes down to 1/8" and even smaller.
     
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  14. NtheBasement

    NtheBasement TrainBoard Member

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  15. Mike C

    Mike C TrainBoard Member

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  16. mmagliaro

    mmagliaro TrainBoard Member

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    Tungsten powder has almost the same drawback as tungsten putty. There is a lot more air space between those granules than you think.
    Tungsten gets you a good 1.7x density boost over lead, but only if you keep it solid with no fillers.
    I use lead sheet too sometimes, when I have enough room and don't need to use tungsten (which is comparatively expensive and hard
    to work with). BTW, if you really have to, you can grind away tungsten with a diamond cutoff wheel in a Dremel. Keep it clamped
    in a vise so it doesn't get too hot, protect your eyes and lungs from the dust, and prepare to be patient. But if you have
    a piece that "almost" fits in a loco, you can grind some off to shove it in there.
     
  17. badlandnp

    badlandnp TrainBoard Member

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    All good advice here. Weight in the right place is extremely helpful. The Bullfrog snot in lieu of a traction tire is a good help, and often times needed. Properly applied it lasts a very long time! One of my Mike's, an Atlas/Riv, with a GHQ boiler kit on it made of pewter had to have the 'Snot." The thing is heavy! The original hard and dry tire enabled it to pull three or four cars. Added a thin coat of 'snot' and it went up to a dozen.

    Weight is great. But traction/adhesion is king. I remember one foggy/icy morning when working in PA. We were moving a unit (loco) for testing. I was on the ground and we were creeping towards a closed door. Brakes were applied, and it just slid along the icy rails. Sand being applied probably helped along with the heat of sliding. We stopped a couple of feet short of the door, with a major pucker factor going on! Adhesion, adhesion, adhesion.
     
  18. DCESharkman

    DCESharkman TrainBoard Member

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    There are a lot of locomotives that can pull,I have has an ABBA consist of IM FT's pull 88 cars at a show. There were no traction tires, just stock. When I run modern like 3 SD80's from Kato they can dwarf the 88 cars and I am not sure how many cars they can pull because I ran out before I could find out. I have run lots of long trains with the Kato locomotives. They are heavier than most the other locomotives out there and seem to have stronger motors.
     
  19. bill pearce

    bill pearce TrainBoard Member

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    I find this discussion strangely accurate and informative, but still bewildering. Like many of us, I live in a city where trans are common, and the last time I wae a string for freight cars being pulled by a single locomotive was, well, never. I have seen short strings pf just two or three cars pulled by a two unit lash-up in switching moves. So, when I planned my Cajon layout, I planned on running three and for unit lash-ups on both freight and passenger trains, to add fidelity to the prototype.
     
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  20. bill pearce

    bill pearce TrainBoard Member

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    As to the statement that you wheels can't be dirty because the locos are new, you do understand that a loco fresh from the factory will have wheels dirtier that you will ever see on your layout? The manufacturers apply a black (paint?) coating to the wheels, and that covers every nook and cranny on the wheels, so your brand new wheels are in fact pre dirtied from the factory.
     
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