Steep down grades

[samike]

I am busy planning a layout around the walls in a 16 ft wide by 21 ft long section of a garage and was wandering what the experience is with steep down grades.  Most of the track would be on two foot wide sections around three walls at 48 inches elevation with a large radius loop (Tehachapi style) in one corner to gain some 5 inches in elevation and then a 31 ft long  climb,  on twin tracks, to a final elevation of 62 inches so as to create a removable "bridge" section with a soffit at 60 inches to allow a family car to be parked below. The problem is I want to have a long continuous loop to run long trains and to get back down to the 48" elevation via the one track from 62" elevation over 14 ft would mean a 7.8% down grade.  The other track would link back into part of the loop at 52" elevation so the down grade would be 4.9%.

Are these down grades too steep or should I adjust the elevations to say 50" elevation for the main trackwork and say a max. elevation of 61" which would give down grades of 6% and 3.2%?  Any thoughts?

Regards Mike.    

[chateauricher]

I am busy planning a layout around the walls in a 16 ft wide by 21 ft long section of a garage and was wandering what the experience is with steep down grades.  Most of the track would be on two foot wide sections around three walls at 48 inches elevation with a large radius loop (Tehachapi style) in one corner to gain some 5 inches in elevation and then a 31 ft long  climb,  on twin tracks, to a final elevation of 62 inches so as to create a removable "bridge" section with a soffit at 60 inches to allow a family car to be parked below. The problem is I want to have a long continuous loop to run long trains and to get back down to the 48" elevation via the one track from 62" elevation over 14 ft would mean a 7.8% down grade.  The other track would link back into part of the loop at 52" elevation so the down grade would be 4.9%.

Are these down grades too steep or should I adjust the elevations to say 50" elevation for the main trackwork and say a max. elevation of 61" which would give down grades of 6% and 3.2%?  Any thoughts?

Actually, a 14" drop from 62" to 48" over 14' (168") is an 8.333% grade (14/168 = 1/12).

Grades of 2% or less are generally prefered.  3% is do-able; but will limit what you can run.  Some mountain logging operations can work with 4-5%.  But, anything more than that is pretty much impossible.

If I were you, I would sit down and re-think my plans.

• Is there any way to have reversing loops on your upper- and lower-decks ?  (This would mean using the same grade to link both decks and eliminate the need for the break-neck 8.3% grades.)
• Can you have the lower-deck at a higher elevation ?
• Can you make the grades longer than 14ft ?

Try to keep your grades under 3% (2% would be better) and you should be fine.  Good luck.

 

[jeffrey-wimberly]

Your projected grade is way too steep! You could find yourself with a runaway train that WILL derail at the bottom. Try for 2.5% or less.

[fwright]

I am busy planning a layout around the walls in a 16 ft wide by 21 ft long section of a garage and was wandering what the experience is with steep down grades.  Most of the track would be on two foot wide sections around three walls at 48 inches elevation with a large radius loop (Tehachapi style) in one corner to gain some 5 inches in elevation and then a 31 ft long  climb,  on twin tracks, to a final elevation of 62 inches so as to create a removable "bridge" section with a soffit at 60 inches to allow a family car to be parked below. The problem is I want to have a long continuous loop to run long trains and to get back down to the 48" elevation via the one track from 62" elevation over 14 ft would mean a 7.8% down grade.  The other track would link back into part of the loop at 52" elevation so the down grade would be 4.9%.

Are these down grades too steep or should I adjust the elevations to say 50" elevation for the main trackwork and say a max. elevation of 61" which would give down grades of 6% and 3.2%?  Any thoughts?

Regards Mike.    

Mike

There are really only 2 issues with a steep downgrade, and both involve the locomotive mechanisms.  Because we do not have functional brakes on our models the questions become:

1) Does the mechanism in your locomotives have enough friction (that is not capable of being reverse driven by the wheels) to hold back the weight of the train on the steep grade?  Although it very seldom happens in model work, it is possible to make even a single thread worm gear system sufficiently low in frcition that it can be reverse driven by the wheels.  What I mean is that if you push the locomotive by hand will the wheels turn and the gears cause the motor to turn.  Non-worm gear locomotives are particularly susceptible to this. 

If the locomotive can free-wheel with pushing, then it cannot hold a long train back on a steep grade.  The load will cause the locomotive to free-wheel and continue down grade out of control.  Steepness of grade and weight of train determine how much force will be applied to the locomotive, but do not determine whether free-wheeling will happen.  It is theoretically possible to set up an engine braking system using BEMF in DCC, but I don't know if any of today's decoders can do this.

2) Is the axial bearing load bearing capability of your locomotives sufficient to prevent bucking under the load of the train?  In a worm gear drive, a load tends to make the worm move longitudinally or in the direction of the worm shaft.  Similarly, when the load is removed (going down grade) the worm trys to move the opposite direction.  The axial play of the bearings limit this movement of the worm.  If there is slop in the axial direction, the locomotive will "buck" going down grade with a load behind it.  First the locomotive speeds up with the worm movement, and then suddenly slows down as the worm movement stops.  The traditional cure for bucking is to add thrust washers (just regular washers) between the worm and the gearbox end to prevent this longitudinal movement of the worm shaft.

The longer the train, and the steeper the down grade, the more force the worm is going to apply trying to move longitudinally.  The grades (both directions) with heavy loads will create wear on a poorly constructed or weak drive train.

Note that if the drive train is free wheeling, bucking will not happen.  So the 2 problems are mutually exclusive - you can have one or the other, but not both.  And neither problem is caused by the steepness of the grade; the problems are solely a result of the characteristics of the loco mechanism.  The steepness of the grade and the length of train only affect the magnitude of the forces involved.

my thoughts, your choices

Fred W

[wjstix]

If you have room for a "large radius loop" you should have room for a helix?? Take a look at this if you aren't familiar with helixes:

<http://www.easyhelix.com> 

[selector]

Most definitely, rethink your approach now.  Even 4% is horrendous, and it makes no difference if you are modelling or on a real railroad.  Modify your ideal height differential so that you have no more than 3%, but the advice to keep it under about 2.5% is good.  What this will make you thankful for, eventually, is that you will actually be able to haul decent lengths of cars back up that grade in reverse if you ever have a need.

[tomikawaTT]

For what it's worth...

On my recently dismantled layout I had a short, straight stretch of 8% grade,  operated downgrade only.  One of my locomotives, which oughtweighed the train it was pulling (large, die-cast diesel hydraulic,) acted as if the grade wasn't even there.  A slightly smaller diesel-hydraulic with a spring belt and worm gear drive bucked like a prize Brahma bull!  My other locos fell between those extremes, but most of them were not happy.

Based on that experience, I've decided to limit my worst downgrade-only bypass track to 4%.  Anything upgrade is limited to my prototype's 2.5% - and hidden tracks will be less.  If nothing else, that will be a lot easier on the rolling stock.

Chuck (modeling Central Japan in September, 1964)

[samike]

Thanks to all who have sent helpfull thoughts.  I will and have been playing around with alternative levels to reduce the steep down grades. Unfortunately, I can only fit a large radius loop in one corner as the other corner will have to, at times, accommodate the bonnet of a small car.

If I raise the all the lower level, around the wall track, to 50" evelation and with a 32" radius loop in one corner reach an elevation of 54.5" (2.23% upgrade) which then continues to split into two parallel tracks and climb to a maximum upper level of 61" over some 32 ft (1.7% upgrade).  I can then bring both the two tracks down from 61", join them into one track which can join the top of the loop at elevation 54.5" over a length of some 17 ft (3.2% downgrade).  This will give me a continous run between elevations 54.5" and 61".  To get back down from the 54.5" elevation to the 50" level I propose to run a track down from the top of the loop, just after the link in from the 61" level and run it on the inside of the twin climbing tracks. I should be able to get back down from the 54.5" to the 50" level over a 17ft length (2.2% downgrade).  If this all makes sense I should also be able to run all the routes in reverse as the grades will be within reason?

 Regards Mike.      

[selector]

Yes.  You really don't ever want to constrain yourself to unidirectional running, especially on your main, if at all possible.  At the least, you would want to even the wear on the wheel flanges over time, and not wear the ones outboard of the curves paper thin.  Also, you really should avoid handling expensive locomotives as the risk of damage rises with each lift and rotation to change directions.  So, it would be best to build in a bidirectional main so that you can enjoy the motion of your trains from both vantages, and permit the running gear and wheels to wear evenly.

Just my