OvermodThat certainly makes it 'not for everyone', but I also don't think it's up to self-appointed forum police to discuss why it shouldn't be the way it is.
Alton Junction
gregc,While friction doesn't scale, we (usually) use a different kind of bearing in our rolling stock models. The needle point bearing offers a lot less starting friction due to the very small surface area in contact with the rotating axle.For an example, the Rapido NH 8600-series coaches came with a plain bearing truck. The axles had blunt ends and fit into brass strips that had holes punched in them. These cars do not roll well, to be kind. The next design, the NH parlor, came with a redesigned truck that had needle point axle ends that fit into dimpled brass strips. These parlor trucks roll extremely well to the point you can't park these cars on any kind of grade or they'll roll away.
OvermodThere are plenty of threads I don't much care for, either, but I just don't read them
+1
greg - Philadelphia & Reading / Reading
richhotrainIn this case, there appear to be at least three of us who feel the same way considering that I was replying to a reply to a reply.
There are plenty of threads I don't much care for, either, but I just don't read them, let alone comment merely about why I don't like them or why they are irrelevant to me personally. Much of what I write about isn't going to appeal to those who only value experience, for example, rather than theory. It just so happens that this thread was started to discuss theory and analytic techniques, not experience per se. That certainly makes it 'not for everyone', but I also don't think it's up to self-appointed forum police to whine that it shouldn't be the way it is because they don't like it. If you don't like it, or don't understand it, or don't want to understand it, or don't want to contribute positively ... you're right, I'm the last person in the world to tell you you can't express yourself, but please don't expect me to avoid discussing theory just because you don't like it.
Overmod richhotrain I like to read through most of the threads that are posted on this forum. But, lately, I find myself unable to enjoy a lot of the technical stuff that is posted that has more to do with prototype engineering than model railroading. And you expected what out of a thread titled 'Model vs. prototype adhesion'? I would prefer to read less of it than more of it. Then I suggest that you do so, instead of commenting about it in threads that evidently don't interest or concern you.
richhotrain I like to read through most of the threads that are posted on this forum. But, lately, I find myself unable to enjoy a lot of the technical stuff that is posted that has more to do with prototype engineering than model railroading.
And you expected what out of a thread titled 'Model vs. prototype adhesion'?
I would prefer to read less of it than more of it.
Then I suggest that you do so, instead of commenting about it in threads that evidently don't interest or concern you.
Rich
richhotrainI like to read through most of the threads that are posted on this forum. But, lately, I find myself unable to enjoy a lot of the technical stuff that is posted that has more to do with prototype engineering than model railroading.
SeeYou190 Well done Robert. That is the funniest thing I have seen in a week! -Kevin
Well done Robert. That is the funniest thing I have seen in a week!
-Kevin
Autumn in the Rocky Mountains, fall gardening chores. I was just spreading compost in the flower beds when the thought came to me.
Robert
LINK to SNSR Blog
i think it's fair to question if our models can pull an equivalent number of cars as a prototype loco. if not, how many
my models seems to be proportionally heavier than prototypes when their weight is scaled by 87^3. and while car weight may similarly scale I think what's relavent is the friction of the cars.
armstrong's chart on bearing friction indicates 6 lb/ton for an MT car at 25 mph or 0.3%. MT cars would be 3 lb/ton. while i'm sure some cars are better, i think 2% is typical value for model rolling stock.
so if the friction of the train is 10x more, i think it's reasonable to expect a model locomotive to be correspondingly limited assuming loco adhesion is roughly the same as the proto (~25%) which i believe it is.
SeeYou190 ROBERT PETRICK If we're having fun with physics, have any of our intellectual heavyweights pondered whether scaling down weight and scaling down mass is the same? Lastspikemike I assume you were referring to me? Well done Robert. That is the funniest thing I have seen in a week! -Kevin
ROBERT PETRICK If we're having fun with physics, have any of our intellectual heavyweights pondered whether scaling down weight and scaling down mass is the same?
Lastspikemike I assume you were referring to me?
ROBERT PETRICKIf we're having fun with physics, have any of our intellectual heavyweights pondered whether scaling down weight and scaling down mass is the same?
LastspikemikeI assume you were referring to me?
Living the dream.
The grass is cut, so here goes.
All theory aside, example #2, the Bachmann 2-8-4. Sorry I don't have more photos.
The Bachmann 2-8-4 was one of the first in a series of regular line products from them that are nearly Spectrum quality.
The drive is very conventional, and out of the box the loco is a little light and a little tail heavy. It also suffers from an awkward drawbar attachment with a long pin extending down from from the back of the frame to allow the trailing truck free swing.
Out of the box it pulled 18 of my piggys.
Since my plan was to convert them to 2-8-2's while improving their pulling power, a new tender connection was necessary.
I added weight, a total of 6 oz to the loco:
The weight was mostly added in the front, balancing the loco evenly on the drivers. Loco weight was increased from 12oz to 18oz
And 2oz to the tender for better tracking.
The original drawbar post was completely removed and a new drawbar was fabricated from brass and is actually attached to the loco where the old trailing truck was attached. Then the new PSC (previously Kemtron) brass Delta trailing truck is attached to the drawbar just behind where it attaches to the loco.
If you look cloesly at the photo you can see the drawbar going up and over the truck and you can see the attachment screw.
Years ago this was a common drawbar design on a number of diecast and brass steam locos. it puts the pulling force in a straight line at coupler level and makes for much better tracking in curves.
Pulling power increased about 40%, and tracking thru turnouts and curves is noticeably smoother.
A little weight and a better drawbar turned this so-so puller into a great puller - about 30 of my 5oz piggys with no problem on level track. I have done five of these like this.
To be clear, I do my pulling tests with about 80 of these:
Kit bashed Athearn 50' piggybacks equiped with Kadee sprung trucks and Intermountain wheelsets - total weight 5.2 oz
Sheldon
Paul3Well, the railhead in HO scale has a sharp 90 degree corner...
Now the point does remain that, in practice, it is very difficult (bordering on practical impossibility) to superfinish or burnish the gauge-corner region so even the neutral running position gives even an order of magnitude of actual contact patch size -- usually erring on larger, rather than smaller, for "practical" adhesion, I think. But the premise of the thought experiment is to scale the patch proportional to the weight and then see how nickel silver under test would react to what is very close to indenter dimensions...
I think he was well aware of the scaling laws when invoking the timeless topic of weight vs. mass ... at least I sure hope so, as it would make no sense otherwise. I confess that all you really had to ask him is 'why all objects in a vacuum at the same point fall at the same speed' to get him to actually look at gravitational physics and answer his own question...
Overmod,Well, the railhead in HO scale has a sharp 90 degree corner and real rail has a rounded top. The contact patch won't be the same. That still has nothing to do with how much something weighs.
Robert,Weight is only a force. Mass is a function of density and volume, which if multiplied by the force of gravity equals weight. Because mass is related to volume, to scale it properly you have to reduce it by the scale ratio three times: once for width, once for length, and once more for height.Think about it. If you took an 87-foot long autorack and sliced 1/87th off the length making it the correct length for an HO version of the same car, you'd still have a slice that's 10-foot wide and 19-foot high. You also have to reduce the height by 1/87th and the width by 1/87th to get an HO scale sized car.
Weight is a cube function and to scale it, you have to reduce it by the scale three times.What doesn't scale is friction or gravity (among other things).
Of course we're imagining the full-scale car or locomotive at the same place on the Earth as the model when we "measure" its characteristics, if you need a little more assumption information...
Does a ten-pound block of steel, a ten-pound block of concrete, a ten-pound block of wood, and a ten-pound bag of feathers weigh the same in HO?
Thanks for introducing me to C. horizontalis. I had no idea!
If we're having fun with physics, have any of our intellectual heavyweights pondered whether scaling down weight and scaling down mass is the same? Does a ten-pound block of steel, a ten-pound block of concrete, a ten-pound block of wood, and a ten-pound bag of feathers weigh the same in HO?
I haven't pondered it, and I also have grass to cut and some cotoneasters to trim.
ATLANTIC CENTRAL Now if you run them with those silly MRC power packs at 16-18 volts like Mike Wolf thinks DC power should be........... I will post my next installment on this subject later today if time allows. The grass needs cutting. Sheldon
Now if you run them with those silly MRC power packs at 16-18 volts like Mike Wolf thinks DC power should be...........
I will post my next installment on this subject later today if time allows. The grass needs cutting.
Paul3Likewise, a 259,500 lb. GP9 would be 0.393 lbs. or 6.28 oz.
Sheldon,Yep. A 40' boxcar that weighs in empty at 46,500 lbs. scales down by 87.1 three times for weight. So 46,500 / 87.1 / 87.1 / 87.1 = 0.070 lbs, or 1.12 oz. At a Load Limit of 130,500 lbs., the same car would weigh 0.197 lbs., or 3.16 oz.Likewise, a 259,500 lb. GP9 would be 0.393 lbs. or 6.28 oz.
Lastspikemike It may be worth pointing out that our scale steam locomotives aren't. The torque delivery to the rails is pretty smooth for our electric motor gear driven models. Anyone observing wheel slip on a real steam locomotive would notice the difference even if not understanding why. I'm pretty sure you do not need to "quarter" the drivers on a model electric motor driven steam locomotive. The parallel would be early diesel powered British locomotives that tied drivers together with external rods. The tricky part about steam locomotives is the drive rod connection to the main driver, not the connecting rod(s). Quartering is only required to accommodate the two cylinder "engine" which our models do not have. Some have been built with three driving cylinders per crank which is even harder to "balance" from a torque delivery perspective. Rapido drives all three axles on its Royal Hudson, MRR gives a detailed positive review of this model in the October issue. Clearly, it would not matter whether those drivers were quartered or not, they don't even need a connecting rod. Another thought relates to scale effects on weight. Length maybe 1:87 but planform is not and volume is even further from 1:87. You can fit 87 scale locomotives end to end alongside the real one but that won't be enough to fill the volume occupied by the prototype. Weight does not scale in part because physics doesn't scale in our real world environment, a 1:87 atmosphere would be problematic, for example. Scale models should really haul @ $ $ because they are pretty heavy compared to prototype. Just as they can reach ridiculous "scale" speeds (which is a very odd concept in itself, given that speed is speed....) although in that single dimension 1:87 holds true. The real area of interesting inquiry relates to the coefficient of friction in the model world. Interestingly, steel on steel isn't particularly good for tractive force but it sure works well for rolling resistance!
It may be worth pointing out that our scale steam locomotives aren't.
The torque delivery to the rails is pretty smooth for our electric motor gear driven models. Anyone observing wheel slip on a real steam locomotive would notice the difference even if not understanding why.
I'm pretty sure you do not need to "quarter" the drivers on a model electric motor driven steam locomotive. The parallel would be early diesel powered British locomotives that tied drivers together with external rods. The tricky part about steam locomotives is the drive rod connection to the main driver, not the connecting rod(s). Quartering is only required to accommodate the two cylinder "engine" which our models do not have. Some have been built with three driving cylinders per crank which is even harder to "balance" from a torque delivery perspective.
Rapido drives all three axles on its Royal Hudson, MRR gives a detailed positive review of this model in the October issue. Clearly, it would not matter whether those drivers were quartered or not, they don't even need a connecting rod.
Another thought relates to scale effects on weight. Length maybe 1:87 but planform is not and volume is even further from 1:87. You can fit 87 scale locomotives end to end alongside the real one but that won't be enough to fill the volume occupied by the prototype.
Weight does not scale in part because physics doesn't scale in our real world environment, a 1:87 atmosphere would be problematic, for example.
Scale models should really haul @ $ $ because they are pretty heavy compared to prototype. Just as they can reach ridiculous "scale" speeds (which is a very odd concept in itself, given that speed is speed....) although in that single dimension 1:87 holds true.
The real area of interesting inquiry relates to the coefficient of friction in the model world. Interestingly, steel on steel isn't particularly good for tractive force but it sure works well for rolling resistance!
Volume and weight are cube equations....
Most of my locomotives run at scale top speeds that are very close to their prototype top speeds - My DC power supply is limited to 13.8 volts, filtered and regulated before it enters my Aristo wireless throttles.
SeeYou190...I used the tender on one of my Oriental Powerhouse Light Mikados. The Powerhouse models have terrible tenders, so the Athearn Genesis tender was an upgrade. The resulting Hybrid model is something I am quite happy with. I hope to find another tender from an Athearn Light Mikado for my last one.
Kevin, I have one of those Athearn tenders, NiB, if you're interested. You should have my e-mail address (via GERN) if you want to contact me, as my "Conversations" feature appears to be out-of-service.
Wayne
Note that as soon as the drivers 'spin uselessly' you are assessing coefficient of sliding friction, with added complications of hydrodynamic lubrication if an appropriate layer of shearable contaminant is present. The actual thing we are wanting to measure is 'rolling adhesion' which involves asperities in one surface rolling at zero slip into interference with those on a stationary surface; nobody's "engineering" testing models so far seem to be concerned with this, and the double-salient influence of gravitational 'adhesion' vs. motor torque to produce lateral motion should not be lost on you. What is needed is a peak-reading forcemeter that gives peak drawbar pull just at the instant before the wheels break loose (we aren't concerned about stall in this context). Rolling stock is a bit more complex: you need a way to brake a wheel rim without putting strain on the axle bearing means, and adjusting the force to read the peak just before slide occurs.
As an aside, trying to assess the moment of slip while reading something like simultaneously reading something like pointer position on a spring scale is nugatory... fortunately in most cases something as simple as a slider moved ahead of a spring pointer would give us rough peak results.
Unless there is a consistent contact patch on both wheel tread and rail much of the variance in conditions far exceeds variance being observed due to frictional effect. Several references very pointedly take up the fact that static 'friction' of quite a few "lubricants", in the absence of factors causing hydrodynamic lubrication shear, can be higher than clean-surface asperity interaction. This can obviously be tested for something like the timeless-topic Wahl clipper oil... but only on track properly and reproduceably prepped, and wheels of known and equally reproduceable tread profile and characteristics.
It's going to be fun to see where this leads...
I decided to resolve some of this by looking up actual research, for example the Maine On2 FAQ discussion very specifically related to the present topic. What I've found so far has mostly been a methodological hash, with most of the actual historical work dancing infuriatingly around what is actually needed to advance fundamental knowledge. I regrettably conclude that some basic research -- actual scientifically-principled research, not calculating 'coefficients of friction by the inclined slope method' by someone claiming nearly a quarter century in the 'friction-reducing business' by putting a scale on model railroad stock rolling downhill -- is going to be required on both the actual alloy composition and the effect of drawing (and then surface prep) before anything better than the current state of anecdotal and empirical research, often full of wack assumptions, can be developed. When I have done some more research, I will put at least a proposed methodology for review here; in the meantime look up the Maine On2 reference and list the issues or concerns you have with their analysis and references...
... and somebody tell me the specific alloy composition of popular brands of track. B10 is about 13.38% nickel, probably the lowest proportion that gives a reasonably 'white' appearance. Conductance still goes down markedly with increasing nickel n this range of nickel concentrations, so the 'less' nickel the better from that perspective. I have the suspicion that at least some rail is actually a nickel brass, or contains additional effective alloying agents at small concentrations, rather than being a binary alloy.
doctorwayneI hope that the word "junked" was not literal, as despite the poor pulling power, the Athearn Mikados were otherwise very smooth runners.
I used the tender on one of my Oriental Powerhouse Light Mikados. The Powerhouse models have terrible tenders, so the Athearn Genesis tender was an upgrade.
The resulting Hybrid model is something I am quite happy with. I hope to find another tender from an Athearn Light Mikado for my last one.
The third Powerhouse Light Mikado I own was upgraded with a Tenshodo brass tender.
I had three steam locomotives I was not happy with. A Mantua 2-6-6-2, a Bachmann 4-8-2, and the Athearn Mikado. I have plans to revive the Mantua and Bachmann, but since I have 5 other USRA Mikados (3 Powerhouse and 2 Sunset Heavies) for my smallish layout, I saw no reason to put effort into fixing the culprit. The tender was put to good use.
SeeYou190The Athearn Light Mikado was junked
I hope that the word "junked" was not literal, as despite the poor pulling power, the Athearn Mikados were otherwise very smooth runners.
SeeYou190...This I know: My Oriental Powerhouse Light Mikados would pull a 12 car freight train around my layout, but the Athearn Genesis Light Mikado would not even pull a six car train around the 24 inch radius curves...
In Overmod's initial post in this thread, there's a sub-quote from Lastspikemike referring to my link to another Forum, where a thread showing a method of increasing the pulling power could be viewed.
While the procedure might not have been all that simple for beginners, it certainly wasn't complicated nor did it require much in the way of special tools or materials, and I think that it was fairly well-illustrated, too.After seeing some of the great work that you do, I don't doubt that had you known of that thread, you could have easily made your Athearn Mike into a decent puller.
A half hour-or-so ago, I grabbed one of my modified Athearn Mikados, then coupled 20 Accurail boxcars, and a TrueLine caboose to its tender. It left the staging yard easily, and then proceeded down a fairly steep grade, and into a similar up-bound grade....
With much of the trailing train still coming downhill, the loco made it onto level track again...
...but once the cars were all now heading uphill, the loco slipped its drivers, and I had to put the 0-5-0 helper into service. This took the locomotive to a downhill run, but with some of the last trailing cars still heading uphill, the loco struggled until all but the last 3 or 4 cars were on level track...
The loco and train then proceeded down a 2.5% grade, and then through a small town on level "ground"....
From there, it entered a fairly wide curve (34" or 36" radius) on a slight downgrade ...
and then onto the longest stretch of level track on the lowest portion of the layout with one major curve of about 34" radius...
Granted, my track curves are at somewhat larger radii than yours, but on this portion of the layout the locomotive handled the train without issue. Total trailing weight (tender not included) was 84oz. or 5.25lbs.
In normal operations, the train would be, at most, 15 or 16 cars, and would have 2 such locomotives.
I"ve worked on a couple of those Powerhouse locos, for a friend, but if they were mine, I would have simply created floors for the tenders, and mounted the trucks in a manner similar to that used on most tenders and freight cars.
Gary
Trainman440There's a trade off. The more "texture" you have on wheels, the more traction it may have, but the easier it will pick up dirt from the track. Those old BB wheels needed a wheel clean after a few hours of running...
While I do agree that those wheels tended to accumulate a lot of dirt, I don't recall ever having to manually clean them. Instead, I'd simply couple the locos to a heavy train and send them up a decent grade. Once the wheels started to slip, the crud flew-off in chunks, faster than your cat sheds on a new custom-made suit.
OvermodDon't like iDrive?
Had to look this up. Down here "I-Drive" is International Drive in Orlando. One of the most fun streets in the entire World. I was thinking... who doesn't like I-Drive?
Just thinking that they could do something other than traction tires with those rubber inserts.
- Douglas
Doughless Couple more thoughts: Adding weight to the extreme front and rear of the loco will improve the tractive effort of the loco....as long as the weight is equidistant from the midpoint of the drivers....or in the case of our models, equidistant from the driver(s) that actually does the work. If the nickel silver drivers of our models are so slippery, why don't they make the drivers out of the sintered metal that Athearn made for their old BB diesel trucks? Electrical pickup problems? Certainly those BB trucks picked up track power decent enough.
Couple more thoughts:
Adding weight to the extreme front and rear of the loco will improve the tractive effort of the loco....as long as the weight is equidistant from the midpoint of the drivers....or in the case of our models, equidistant from the driver(s) that actually does the work.
If the nickel silver drivers of our models are so slippery, why don't they make the drivers out of the sintered metal that Athearn made for their old BB diesel trucks? Electrical pickup problems? Certainly those BB trucks picked up track power decent enough.
There's a trade off. The more "texture" you have on wheels, the more traction it may have, but the easier it will pick up dirt from the track.
Those old BB wheels needed a wheel clean after a few hours of running.
Also I prefer the look of nickel plated wheels.
Charles
---------------------------------------------------------------------------------------------------------------
Modeling the PRR & NYC in HO
Youtube Channel: www.youtube.com/@trainman440
Instagram (where I share projects!): https://www.instagram.com/trainman440
DoughlessIf the nickel silver drivers of our models are so slippery, why don't they make the drivers out of the sintered metal that Athearn made for their old BB diesel trucks?