Weight Effects

[AKNscale]

So I've heard this come up quite a few times, especially when discussing milling frames in N for decoder installs. The question is aimed at the experienced guys as I've yet to see any issues in what I've done so far(I understand the theory, but I want to know in practice). I'm curious as to how much you guys think that milling the weight off of the frame would really affect performance/pulling power? I definitely understand that on an extremely lightweight loco like the Atlas MP15, everything counts. But on a GP40/38, I can't see the milling really affecting it. I say this based on the locos that I have with LOKsound decoders installed in them and I've seen no lack of pulling power from when I bought them to now with the decoders installed. Just curious if any of y'all have had a different experience and what exactly you did to get there?

[jagged ben]

Have you done a carefully controlled study?  Does your layout have grades?  How much were you stretching the pulling power already?  Physics says there will be an effect, it just may not be that easy to quantify.  In my experience an Atlas 4-axle pulls about 10-12 cars up a 2 percent grade, depending highly on the cars.  If that reduces by half a car with weight removed for a decoder, would you notice?   Well it means that with 4 locos my pulling power might be reduced from 48 to 46 lighter cars or from 40 to 38 heavier cars.  As you can see, if I'm just counting cars then the variable weights of the cars masks the difference made by lighter locos.  Hard to tell, from casual observation, how much is the locos doing worse vs if the train just happens to be heavier.

I just wish they would still make lead alloy frames.

[Rossford Yard]

This comes up every so often, and once upon a time, someone took the time to figure that out (so long it may have been Atlas forums, not sure)

At any rate, they concluded that the miniscule loss of weight didn't affect pulling power. I have never added weight to GP or SD units. I did add metal weights in the cabs and around the pilots and steps of my MP15 locos, and it did seem to help them pull more at least marginally.

And my solution was to switch with the GP 38 in most cases.  If it doesn't run/pull great (longer wheel base helps with stalls and jerking as well) there isn't much reason to run it, unless your road only used switchers.  None of them pull well enough for my taste.  Sound decoders might make an additional practical difference as well. I have the IM SD40-2 and haven't noticed on 16 car trains on 2% grade.

[C855B]

... I just wish they would still make lead alloy frames.

This.

I think the question being posed is interesting in that we're probably talking about "modern" frames from the post-lead-alloy era. Carving away frame for circuitry and a speaker certainly carries a penalty in available traction weight, but not like it would if it was an old-formulation frame. I guess what I'm saying here is modern frames are too light already, so what's 10% less of not enough in the first place?

Case in point is recent (like two days ago!) testing on my layout. Not scientific by any means, but revealing nonetheless. It started with a project loco based on a modified old Con-Cor U50 frame - 1970s vintage. I suspect it is a lead-content alloy, but don't know that for a fact. This thing pulls a 40+ car train up 2%, with one motor and only four driven axles. Then I try a modern "large" diesel - B'mann DDA40X - with the same train. It has two motors and 8 driven axles, and was all wheelslip all the time - on 1%, never mind the big grade.

Then I consider the semi-modern Atlas in the fleet, two samples are a C630 and an SD24, both roughly 10 years old. Each are into wheelslip on the 1% with no more than 10-12 cars. These are obviously way too light.

One constant I just noted with the poor performers is >4 axles. I need to reach into my bag of Geeps and see how equivalent chassis perform with fewer wheels on the rails spreading the (traction) weight around.

Also useful in the comparison is the new ScaleTrains.com turbine. It is two powered 6-axle units. One unit will not handle the test train on the 2%, but is OK on the approach. The two units together, no problem. These are notably heavy for modern N power, being full-width carbodies, but I really suspect if the frames were of an "old" formulation, one would be more than enough.

Hopefully there's some intel to be had from this. The takeaway I get is 1) modern N scale frames are too light; 2) more axles are not better; and 3) milling a modern frame for sound components isn't going to be much of a penalty, there wasn't enough there to begin with.

Anyway, we all know that lead-alloy frames are not coming back. The future is tungsten (denser than lead, i.e., more weight per cubic centimeter), but it is impossible for mere mortals to machine and ghastly expensive to cast and machine in production. I'm currently looking at weights marketed to the Pinewood Derby crowd in various configurations that could be put in nooks and crannies.

[AKNscale]

Thanks for the responses guys

Jagged Ben: No, no carefully controlled study. My layout doesn't but my club's layout does, which is why this question came up. I had noticed that one GP40 would pull 15+ cars up the helix at the club without having a hard time, milled frame or not (side note- all of my freight is metal wheeled). I guess I should do a pull test and post my results and see what others may have seen.

Rossford Yard: Yeah, it tends to come up when I show people a LOKsound install, or I see any other work requiring frame milling. I agree, although I've really come to like my sound Atlas S-2s. Before I bought those, my MPs aggravated me so much I'd given up on them completely.

C855B: You are correct, as I have zero experience with the previous generation of frame design (I re-entered the hobby in 2009?). Interesting results, I wonder if that's much like here(when I was in the army we had quite a few guys move up here [Alaska] from the south. They'd put big, wide mud tires on their trucks and claim that they can drive them all year because the traction patch was bigger and will therefore stick to the road better. Then winter would hit and many of them would end up in the ditch). My thought being like you in that maybe the extra axles hurt the tractive effort. You'll certainly have to let me know your results with the GPs as I'm curious. I'd be interested in what you find with the pinewood derby weights and where you'd put them.

Just from the three responses here it seems that the answer is basically, not much of a difference for a newer style frame. It's also based on the car weight/loco setup(I wouldn't even bother testing my MPs).

[garethashenden]

One thing that comes to my mind with 4 v 6 axles is that unless your track is absolutely perfect you may only have three wheels on the track per truck. Assuming the track is rigid (all put some Kato ones are I believe) they will behave like a stool. If a stool has four legs and is on an uneven surface it will rock. However, if it has three legs it will always be steady. I reality N scale track is quite rigid and this shouldn't really be an issue, but an extra rigid axle does exacerbate the problem. Three rigid axles give a lot more opportunities for one axle to not be in contact with the rails, therefore decreasing traction.
Overall, adding more weight is an easy solution to the traction problem, but there is still a fundamental problem of getting all the weight to the rails and the solution to that is functioning suspension. It's really hard in a scale as small as N and practically everyone (myself included) chooses not to bother, but it would give better performance if done well.

[MK]

What about metallurgy of the loco wheels?  Maybe have better metal formula that would "stick" better to the rails?

[C855B]

I just spent the last couple of hours running trains. (Oh, the humanity. ) Conclusion I came to was a great big fat "IT DEPENDS". There is no pat observation, other than "weight matters, to a point." The lightest of the bunch were Atlas SD24s, already mentioned, and they couldn't pull crap up the 2%. All four were good for maybe 15 cars each, and, yes, it was underscored by it taking three of them to get the 42-car train up the hill.

The Geep theory is so much wishful thinking. All of the four-wheel power I had handy was good for 20-25 cars, 'cept the old Atlas U25B, which reached its limit somewhere between 15 and 20. A Kato SD40 (DCC-compatible version) would do 25 but not 30, as would the B'mann Centennial. @MK is on to something regarding wheel composition; it jogged memory of discussions here several years ago regarding "old" vs. "new" wheels on the Life-Like GP20, revealing that the newer blackened wheels had half the traction of prior production.

If I want to get serious about this - likely a future project - I might take something like an SD24, pop the body off, and add weight incrementally until something smokes the ammeter indicates some arbitrary "too much" value. But not today.

[Santa Fe Guy]

For those times when you want to add additional weight to N Scale locos or rolling stock this product can be very handy.
https://www.deluxematerials.co.uk/gb/rc-modelling/83-liquid-gravity-5060243900470.html
Might be something to try.
Rod.

[peteski]

Remember that it is not just pulling power that is affected - the reliability of electrical pickup will also be negatively affected by deceasing the weight of the model.

[MK]

For those times when you want to add additional weight to N Scale locos or rolling stock this product can be very handy.
https://www.deluxematerials.co.uk/gb/rc-modelling/83-liquid-gravity-5060243900470.html
Might be something to try.
Rod.

Available in the US from Amazon.

https://www.amazon.com/DELUXE-MATERIALS-Liquid-Gravity-Weight/dp/B0047YORDQ/ref=sr_1_1?ie=UTF8&qid=1499653872&sr=8-1&keywords=liquid+gravity