Obviously no suspension or compensation in the loco itself?

Dear Toni,

Any idea how flexible (or otherwise) the loco itself was?
Any compensation or even "slop" in the mech to speak of?

Happy Modelling,
Aim to Improve,
Prof Klyzlr

I'm sure there was "some"

"some", but not enough is the only answer I can give you.  I don't know the manufacturer of the loco.  It is an N scale 2-10-2, so I am guessing it is a Bachmann.  I will ask Mike and Josh to bring it again to our next setup so I can get some measurements.  I think my .5% per 100 foot rate of change is still a good rough starting place, but not sure what other folks use.  This is probably about the longest rigid wheelbase we'll have to contend with, although the "Big Boy" may have similar problems.  Usually the articulation allows for tighter radius curves, but vertical curvature (humps AND dips) may actually be more of a problem.

  If I had to guess, I'd say there was no more than .010~.015" of vertical slop in each individual axle.  I doubt that there was ANY sprung drivers, but I could be wrong on that.

Toni

Trying to fully understand

"Out of that I developed my own standard of 0.5% of gradient change per 100 feet."

I am trying to see if I understanding your comment above.  At .5% per 7.5 inches (100 ft in N scale) it will take 30 inches to transition to a 2% grade.  In HO scale that would take 55 inches.   This seams to slow a rate of change, so I think I am missing something. 

I agree that this could be something that could be experiment on.  Anecdotally, I have seen transitions to a 2% grade done in 87 feet (1 foot in HO) that did not seem to be a problem.

I could see a dip of 0.30" over a distance of about 6" causing a problem, if that 6" included the grade down and then back up.

Art     

You got it Art!

  You have done the math exactly right.  It takes 30 or so inches to transition to a 2% grade and another 30 to transition back.  I wanted to make CERTAIN that I would not be introducing problem areas with too abrupt a transition.  The funny thing is that I had to come up with my own "standard", even the NMRA pages just suggest using "gradual" curves, but no good hard numbers or formulas.

  Which is kind of why I posted.   I am curious on not just what folks have seen used and seemed to work, but the methodology that was used to determine how they came to their answers.  

Toni

Quick CAD test

Toni,

Either my CAD program or my computer seems to be misbehaving today, so I can't give you the rendering I was hoping for to illustrate the point, but here's what I did:

I started with a drawing of a USRA light 2-10-2.  It has a rigid wheelbase of 21', and the front of the pilot (actually coupler face) is 35'11" ahead of the rear driver centerline.  I then added NMRA N scale flanges (.022", or 3.5" scale).  With that, I drew a circle from the rear driver to the front of the pilot, and which did not allow any of the flanges to reach above the rail.  The radius came out to 311'2", or 23.33675" actual.  That tells me that the maximum vertical curve radius which a perfectly accurate N scale USRA 2-10-2 could negotiate would be just shy of 24".

Here's where my CAD program froze, so I could not measure the reverse situation with the engine cresting a grade, but I believe that the radius would be less, so if you want a single standard, the one listed above ought to do it.

Using the numbers above, I did a little checking.  That radius over than distance is a change of 6.6 degrees, around 5.8%.  That's WAY sharper than your 0.5%/100' rule, around 4x more abrupt.  Now, I did an absolute worst case scenario (what would it take to lift the flanges off the rail and/or drag the pilot), so perhaps a little more moderation would be useful as a standard.  But, perhaps it suggests that 1%/100' might be a better rule for something roughly the length of a 2-10-2.  Of course, for significantly longer locomotives with no vertical play in the drivers, longer transitions would be needed, but I suspect that anything longer would have at least a little vertical articulation built in.

To me, this underscores the need for some sort of flexibility in a steam locomotive chassis, because a rigid frame loco will left a tread off the rail with ANY vertical curvature.

Very Interesting

Ken,

You are shedding some interesting light on the subject.  I have always eye balled my vertical curves and error on the generous side.  It would be interested in seeing what it would really take if looked at mathematically.

Although I am in HO scale, lets continue to look at this in N scale.  If a perfectly accurate N scale USRA 2-10-2 could negotiate a vertical curve radius just shy of 24", then it would only take 24" to go from horizontal to vertical (climbing the wall).  Extrapolating from there it would take 12" to transition from horizontal to a 45 degree or 100% grade, 6" to transition to a 22.5 degree or 50% grade, and 3" to transition to a 11.25 degree or 25%. If we continue the process we will find that it only takes .24 inches to transition to a 2% grade.  (in HO Scale it would take .44 inches)

If my math checks out, then even if you where to increase the vertical curve radius by a factor of 8 (24" X 8= 192" radius) it would still only take 2 inches to transition to a 2% grade. (in HO scale 3.52 inches)

Math Check?

Art

Math, and reality, check

My drawing suggested that a 24" radius curve was the absolute maximum the USRA 2-10-2 (with NMRA spec flanges) could handle without lifting a flange above the rail.  That doesn't mean it would stay coupled to anything else, or that the lead or trailing trucks would have enough vertical play to stay on the rails.  The only dimensions I included were the rigid wheelbase and pilot (assuming the pilot is a scale 6" above the rail).  It also does not take into account the fact that the model will not exactly match the prototype dimensions, but may be longer.  Thus, the actual minimum radius will almost certainly be a little larger than my numbers suggest.

I would not be surprised if an N scale 2-10-2 could indeed run inside a 4'-5' diameter wheel.  Whether it would stay coupled to anything else is another question.  Longer cars would probably present a problem, just as with horizontal curves.

Also, just like a horizontal curve, you do not want to just jump into a vertical curve.  The transition is the important thing, and understanding how the engine moves in a curve will help us understand how sharp the transition needs to be.  Like you, my preference is to eyeball the curve and err on the generous side, but it would be nice to have at least a rough idea what is practical.  A rate of 0.5" per 25' (1/4 of Toni's original suggestion) means that the grade will vary by roughly 1% under the length of our 2-10-2.  While it may be able to handle that, it seems a bit sharp for me, thus I proposed 1%/100' (.05%/50') as a reasonable compromise.

Art's math ...

  Just a little off on the math for your wall-climbing train.  The path is an arc, so you would need to use the sine of 45 degrees for the length it would take to get there.  For the 24 inch radius, that works out to 16.9" ( you would climb from 45 to vertical in the remaining 7.1").  

  The other thing about Ken's calculation (I think) is the leading and trailing truck.   Wikipedia lists the 2-10-2 wheelbase (without tender) as 40'4", and Ken calculated how much curvature it would take before the flanges cleared the top of the rail.  In all likelihood, you would lose MUCH of your tractive effort WAY before that limit was reached!  I am sure that the drivers on the real thing are sprung and equalized, but how many drivers would need to be "off the ground" to stall a locomotive starting to pull?

  I will have more "hard" measurements after August 24th.  If anyone has one of these locos in their roster, grab some shim stock or a set of feeler gages and tell us how much it takes to lift a driver tread off the railhead.  Either shim the center driver until you have clearance at the front or rear, or shim the pilot truck until you lift the front driver.

  Ken, you are right about also needing to consider overhang past the pivot point.  Picture and 86' flat coupled to a 50' boxcar.  If too abrupt a transition, even a smallish "hump" can cause coupling problems - especially in N (or N scalers using Z scale couplers).

Toni

Rate of change for vertical curve

     I recall having this discussion a couple of years ago and IIRC I worked it out that 1% of change per car length was a good number to shoot for.    For a rigid frame loco I'd measure the height of the flanges then keep the rate of change to less than 25 % of the flange height over a distance equal to the driver wheelbase. That should keep 75% of the flange depth doing it's job. Of course staying on the rails is only part of the problem and a loco with less than full wheel contact will have some traction problems too. Using the N scale loco numbers given in the previous post .022 flanges" / 4=.0055 /1.57" wheelbase=0.35% per 21 scale feet or somewhat less than the rate of change for freight cars.. ..DaveB

I agree a 24" radius vertical curve will not work

However, after re-reading my post, I see I was not completely clear in what I was getting at. When I mentioned that if you increased the radius 8 time it only required 2 inches, I did not mean to convey that 2 inches was the answer, only that a dramatic increase in radius increased the length a little bit.  

The challenge I am having with using a standard of 1%/100' is it makes it sound like (although I know it is not the intent) ever 7.5 inches the track is going to be raised another 1%.  I like the idea of a vertical radius because it continuously changes the grade.  To take things to the extreme one could even calculate an easement.

A 1%/100' grade change would be equal to a vertical radius in degree of curve of .573 degrees, [Tan (1/100)] or a radius of 9999.26 feet [((360/.573)X100)/2PI)].  In N scale that would be 103" radius curve.  In 3rd PlanIt I drew a 103" radius and drew a tangent line at a 2% grade from the horizontal.  It only took 2 1/16" to go from horizontal to the 2% grade tangent.  Even when I doubled it to 206" radius it still only took 4 1/8 inches.

Since it would be be difficult to make a vertical circle with a radius of 206", I would go back to using % per feet, but I would recommend something around 1%/30' grade change.  This would allow 4.5" to transition to a 2% in N scale and 8.25" in HO.

Just my thoughts.  The only thing left for now is testing or real world experience.

Art

Toni, your right!

I new there was something with my math.  So if we use 17" instead of 12" we would have got .34 inches to reach a 2% grade with a 24" radius. 8 times that would be 2.72".  My about post recommending 4.5" would be even better at (13 times).

I could also go with what Ken said of 1% per car length (50').   In reality I think we are right back were we started which was just to eyeball it.  

Art 

More info - unfortunately no pictures (DOH!)

  Today we had our PNW FreemoN meet and Josh brought his long driver wheelbase loco.  I was wrong about what it was.  It is a Model Power 4-8-2.  and a .060 Hump in 12" is enough to lift the pilot truck WAY off the rails!  just looking at it with my "machinists eye", I would estimate that a hump of about .015" under the front driver would be enough to suspend the center two drivers' treads off the railhead.  Putting that amount of shim under the front drivers brings the pilot truck to the limit of it's travel as well. 

The reason I bring it up is that my formerly flat and true trackwork has developed a swale near the faceplates and the type of locomotive REALLY doesn't like it!  The diesels chug right through (I don't have a DD40AX to check how much clearance there is between the fuel tank and railhead)

Next time I will get pictures.

  A couple of thoughts on what caused this.

1. building the modules in the cold garage during the winter months and something expanded/contracted warping the module (no foam used in this construction.

2. I primered the underside of the subroadbed and module frame, but have not yet painted the fascia and did not paint the subroadbed before gluing the cork roadbed down.

3. The surface the modules were built on was warped and the two faceplates are not parallel to each other (checked the bench with my straightedge when I got home and it is pretty darn flat/straight - less that .015" over 48")

4???  Gremlins - Murphy???

I will examine the problem further this week and see if I can come up with a fix and a cure for future modules ...

Toni

Since your 206 radius works

Since your 206 radius works you might just try a way to use it. 206 inches divided by 12 is 17 feet 2 inches.Get a string that long and some chalk. Stretch the string and draw an arc about a foot in length on a section of plywood. You would only need a section a few inches in length to handle the transition and your done. You now have a short section of plywood to use for your vertical curves.

Turns out I did get a picture

I did get a picture of the vertical "hump" that is giving our steam locos fits with the module joins.  It doesn't look real bad here and the little diesels go across it just fine.  I will get a better picture of the problem area tomorrow.

Wow - this thread got a mention in the "What's new"

Just this afternoon I finished editing the video of the "hump" in my FreeMo modules, and how I went about fixing it (I hope).

I have ordered a Bachmann 2-10-2 for further testing on a definitive answer on the maximum rate of change (at least for N scale)

Toni

... and a bit more math

  I may not have explained myself clearly before about restricting the rate of change of the gradient.  I did not mean to suggest that the track was going to be angled at each 100 scale foot increment by a half percent.  I just meant that the smooth curve for our easement should pass through these points.

  So for N scale, a half percent grade equates to .034" every 7.5".  With my experiences of yesterday straightening out the hump at the module joint, I know that the 'ski jump' at the end of the module was not much more than that, and the steam locos were having problems with it.  The 'ski jumps' DID violate the rate of change rule, in that there was not a 7.5" level track between them, but the steam train was in trouble way before that point had been reached.  The hump at the joint between module sections was roughly .040" per 6"

  Using the above numbers in my CAD program, I drew lines that increased grade by .5%, until I reached 2% grade.  Fitting a 3 point curve to this slope resulted in a real world 41.7 foot radius curve! (500.4")

  Some of this may have to do with the fact that you can only scale so much linearly.  Bearings and bushings still have to have real-world tolerances to work, they cannot be scaled down just because the model is smaller.  Even though the teeth on the gears need to be smaller, the clearance and mesh still needs to be the same as their larger scale counterparts.  This works against us in this case because the mechanisms can only have "so much" slop in them before they jam and bind up.  Modern manufacturing has improved the running characteristics in newer N scale steam locos by HUGE amounts in the past 20 years. An HO scale locomotive may be able to handle a far wider range of track conditions than their N scale bretheren (though I am still amazed at some of the track I have seen our rolling stock navigate successfully!).

  More to come once I get my hands on a 2-10-2!

Toni

 "Using the above numbers in

"Using the above numbers in my CAD program, I drew lines that increased grade by .5%, until I reached 2% grade.  Fitting a 3 point curve to this slope resulted in a real world 41.7 foot radius curve! (500.4") "

I wouldn't try to equate a vertical curve to a radius, VC's are parabolic and very gradual compared to our layout's horizontal curves. I think it's easier to work in rate of change per length unit and measure the vertical deflection with some kind of feeler gauge. The one half percent per 100 scale feet rate of change should be more than enough.    An N scale 10 driver  loco might have a driver wheelbase of 24 feet, so if it's balanced on the center driver a hump of .0055 would be 1/4 of an N scale flange ,leaving 3/4 of the flange doing it's job.  12 N scale feet = .90"  so .0055/.90= .0061 or .61%  or a bit more than .5% ( and note that  rate of change per length of desired equipment is what matters, not rate per 100 feet unless you are running 100 foot wheelbase  locos) .......DaveB

More fuel on the fire

While the flange may still be engaged inside the track gage, the tread of the driver is not touching (or barely touching) and doing very little to help propel the locomotive.

Another factor to consider is that the clearance for the "air hose" above the top of the rail is .010" in N scale.  Any gradient change that would cause that to drop below that level should probably be avoided, especially in areas where grade crossing, diamonds, or switches may be encountered.

I received my Bachmann 2-10-2 and did some testing, but it is a much more flexible design than I had anticipated.  The model had no problems with the bad section of track and rolled right through.  The Model Power 4-8-2 that was encountering problems must have much less travel in the design of its wheel system.

One other consideration is that I am trying to come up with a standard that will allow ALL locomotives to run on the Freemo-N mainline (or sidings/spurs).  Since this is not like a personal layout that will only see a specific collection of rolling stock, the recommendations should be broad enough to allow the widest reasonable variety of trains to run.  Much like clearances for tunnels and bridges - they need to be big enough for double stacks and modern passenger equipment.

I know that some people looking at this problem as "what is the MAXIMUM that I can get away with" rather than "what is a safe value that allows for errors and still works".  

vertical curves

The prototype has done the work for us.  The maximum allowable rate of vertical change is 1" in 62', which works out to .0013 or .13%.  I model in HO scale and use maximum superelevation of .040" which is achieved in eight .005" 'steps' every 3 1/2", so achieving .040" of superelevation requires a run of 28" (8 steps at 3 1/2" per step).  For what it's worth, my minimum radius is 48" and the transition to maximum superelevation is achieved within the 28" long easements.  Superelevation of .040" in HO scale is on the light side, roughly 3 1/2", relative to the 5" and more often used by the prototype.  I settled on .040" after experimenting within a range of .030" to .060".  Superelevation of .040" looked good and did not create any operational problems.  I should add the trucks on my cars are set up very tight, with very little free motion.  This avoids toy-like wobble as the cars roll down the rails but requires smooth, precise track work which is free of abrupt transitions.  Finally, the prototype design parameter of 1" in 62' is an accurate but general guideline.  Prototype practice no doubt varies from railroad to railroad.  Good luck!

Ted Shasta

I have ordered a Bachmann

I have ordered a Bachmann 2-10-2 for further testing on a definitive answer on the maximum rate of change (at least for N scale)

Toni

This has GOT to be the longest way round and most contrived complicated drawn-out far-fetched excuse that I have ever seen concocted to justify buying another loco........................

I think I see a construction flaw

The rather thin plywood subroadbed leading to your module joint is cut across the grain. In my opinion, unless you put several shims/supports under it, it will probably continue to warp. I know that the inner lamina of plywood is cross-grained with the surfaces, but it is the surface grain that matters most and the fewer the laminations in the plywood, the more likely it is to warp. It was probably flat as could be when you built it and it sagged afterwards. The transition between modules would actually be a very sharp vertical angle in your case. It looks like a straight section butted next to a concave section. The hump looked huge to me - more like a vertical kink with an angle rather than a radius.

Sags, humps and construction

I agree with J Marlett's obsevations.  From the camera closeups in the video, it looks like photo laminated panels.  This is usually applied to composite type panels.  I did not see any evidence of multi layer plys. This is very weak material.  It definately needs a strong support underneath, glued at 90 degrees to the sub-roadbed, and continues completely from cross brace to cross brace.  This stuff will sag from it's own weight!  Dave

Toni, A similar situation

Toni,

A similar situation happened when one of my fellow club members was building a curved turnout based on some existing curved track. While the turnout was being constructed the most rigid wheelbase locomotive we could find was used to be sure it would negotiate the curve in the track which connected the two parallel lines. In my case it was a high wheeled 2-10-4 of the Pennsy with an equally long tender that had 8 wheel trucks. It was not the only one we also used critters and other short locos to cover the tracking and operational issues, all present issues when dealing with curves, humps and sags.

The idea of using the least forgiving equipment is a good one as then all equipment can be operated. One might also test the longest freight and or passenger cars to be run as well. Long equipment has many issues that can present themselves besides wheel base issues. Overhang can be a real problem and might be much greater than what is present on locomotives with the exception of the 0-8-0 and 0-6-0 variety which often have lots of locomotive floating out in space ahead of the drivers.

The idea of testing and developing a standard is a good one. For over hangs in might be wise to consider 1/2 the distance between a coupler trip pin and the ties over a distance that is equal to the distance from the wheels to the car end on your equipment that has the greatest distance. I would also suggest checking that distance and the height of the lowest portion of a steam loco pilot.

The idea of transitions for vertical curves is a good one and a likely template could be developed and employed that would make sure all things remain functional. On our club layout we have had lots of folks work on things and in the past some members have decided that if the space was not sufficient for the standards that were initially put in place they would be modified so the track would fit and the standards would be ignored. That has resulted in major sections being reworked for many different things such as grade, scenery and curve radius just to name a few.

This picture shows our test locomotive mentioned above pulling a freight of around 50 cars up a grade that is about 2.5% peak instead of a bit over 4%. This locomotive has had around 5 ounces of lead added to it to increase it's pulling power and improve it's tracking characteristics. There were also sections that were not adequately "smooth" in terms of gradient transitions which resulted in sags and humps through the curve. After having experienced what happens when standards are ignored it is nice to see someone trying to develop some that can be called universal dealing with the situation. Your n scale standards will likely be unique to your scale as each scale seems to have it's own particular issues for manufacturing tolerances and short cuts that the manufacturers have taken over the years.

Thanks for sharing your work so far I will be interested in reading your results in the future.

Thanks!

@ Ted,

  Thanks for mentioning the prototype specifications!  I sometimes get hung up on only researching in the "model" world for "model" problems and forget to look to the real thing to see how they handle it!

@ Gary

Nice reply!  I wondered if anyone would see through my veiled reasons for the acquisition of more motive power!

@ Jim & Dave

Yes, the 5mm plywood was an experiment that will not be repeated.  While I was able to fix the problems fairly easily, I am looking at other solutions that don't introduce as many problems to begin with.  I considered using it to make a spline sub-base, but then decided that using foam and being careful with bonding, sanding and construction give the biggest "bang for the buck"

@ Rob

Glad to hear you're following along.   It really was my intent to get the conversation started and see where it would take us ...