Yet Another Helix Design

Sugar Beet Guy's picture
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I needed a helix to get between levels on my layout but I had other requirements besides
diameter and grade. The helix is at the end of a peninsula and I wanted to have track and
scenery on both levels on the outside of the helix.  This meant the helix needed to support
a smooth backdrop as well as upper foam benchwork, track and scenery. Finally, splice
plates weren’t feasible because of the grade and the required vertical spacing.

The track radius in the helix 28” with a rise of 3.75” between laps (2.13%). I’m using ½”
plywood for the sub-roadbed, giving 3 ¼” vertical clearance. I’m not using any other
roadbed because of the tight clearance. I’m not concerned about reducing noise in the
helix since that will give operators a clue that the train is still moving. The track is glued
directly to the plywood with Woodland Scenics Foam Tack glue.     

Since I wanted a smooth surface on he outside of the helix, I cut circular segments from
plywood and used a glued lap joint to join the segments. I used Cadrail to figure how
many segments I could squeeze in then laid out the pattern on plywood sheets. Each
segment was 5 ½” wide to allow clearance for vertical spacers and range in length from
225 degrees of a circle to fairly short segments. I was able to get all five laps of the helix
from only two 4’x8’ sheets of plywood. 

 

To join them I used a router to mill a 2” wide notch on each end, exactly ½ the depth of
the plywood. I was surprised how much sawdust you can generate doing this! Once all
the notches were milled, I assembled multiple short segments together to form larger
segments about the same size as the biggest pieces. I used Tite-Bond III to glue the joints.
The smaller segments were sandwiched between two larger segments to make sure they
were nicely circular. The joints were clamped overnight to allow the glue to develop full
strength. . Aluminum foil was used between layers to prevent the sandwich from gluing
itself together. 

 

Note: I did a small test case prior to assembling all the pieces to see how strong the joints
were. After setting overnight the joint itself was stronger than the plywood. When I tried
to break the joint, the plywood delaminated before the joint gave way. Tite-Bond III is
good stuff.

The helix was assembled a lap at a time. I screwed down a segment to spacers on the
segment below using thin washers as shims to ensure the helix had a very slight super
elevation. All the track joints are soldered to make sure no kinks develop. Next I glued
the track in place and used masking tape to hold it in alignment.

I placed the next segment in position at this time and glued spacers on top of it. The
vertical spacers are staggered so I could glue and screw them from below and above.  The
spacers also hold the shelf brackets for the upper foam benchwork as well as ¾” standoffs
for the backdrop.

After allowing the Foam Tack and Tire-Bond to set overnight, I lifted off the next
segment and screwed the spacers on from below for strength. The holes for the screws
were slightly countersunk so the screw heads would not cause alignment problems. 

The track masking tape was then removed and the track was wired and tested. I ran bare
copper 12 gauge wire on both the inside and outside of the helix track to connect DCC
feeder wires. After ensuring the track was electrically and mechanically perfect, the next
segment was begun.

The final helix section has an increasing radius to allow the track to transition to the foam
benchwork on the outside upper level. The grade of this section levels off to meet the
foam.  

 

Finally, the shelf brackets and backdrop supports were added to the vertical spacers. The
backdrop supports are ¾” thick so that most of the shelf bracket did not protrude through
the back drop. Notches were cut in the Masonite backdrop to clear the brackets with
drywall tape and spackle covering most of the bracket that was visible. 
  

The finished helix is very strong and stable.  It’s a shame it’s hidden by the backdrop. 
People can still climb into the middle to see all the construction if they desire. If I ever
decide to have a dispatcher, the center of the helix will make a nice four foot diameter
office hidden from the view of the operators. 
 

 

George Booth
Director of Everything, The New Great Western Railway
http://users.frii.com/gbooth/Trains/index.htm
 




LKandO's picture

Why the Buss Line?

George, if the entire length of track in the helix is soldered rail why the need for the buss through the helix? The resistance of the nickel, silver, and zinc rail alloy for the total run of your helix is an almost unmeasurable small number.

Alan

All the details: www.LKOrailroad.com        Just the highlights: MRH blog

When I was a kid... no wait, I still do that. HO, 28x32, double deck, 1969, RailPro

Sugar Beet Guy's picture

Why the track buss?

The resistance of nickle silver rail is not insignificant, according to all that I read on DCC forums.  The rule of thumb is to have a feeder for every three foot section of track - for every piece of track for that matter. The major reason for the rule is to avoid depending on rail joiners to pass current.  But I think there can be significant loss along the rails when you are drawing an amp or more.

I strip 12 gauge Romex for the normnal track bus (white and black wires) and I had lots of bare copper ground wire left over. It took a little extra time to staple down the wire and put a feeder on every three foot section but that was a very little time compared to the overall helix construction time. 

The total length of the helix is 75 feet. I feel pretty good about the power in the helix. It's definitly overkill since there will be at most two engines on the helix at any one time (double headed trains). But should a solder joint fail, I am well covered electrically.   

Better safe than sorry?   

George Booth
Director of Everything, The New Great Western Railway
http://users.frii.com/gbooth/Trains/index.htm

Geared's picture

Helix

That is one nice looking helix, George. The way you finished it for scenerey andblending in with the upper level is very nice. Most people hide the helix in mountains, etc. Well done.

Roy

Roy

Geared is the way to tight radii and steep grades. Ghost River Rwy. "The Wet Coast Loggers"

 

Sugar Beet Guy's picture

Why the Buss Line?

I did a quick Google search and found an excerpt from a DCC book by Mike Polsgrove. He measured code 83 nickel silver rail resistance at 0.057 ohms per foot. This is compared to 0.0025 ohms per foot for 14 gauge solid copper wire (I’m using 12 gauge). The resistance of my 75 foot helix track would be about 4.25 ohms, 8.5 ohms across both rails. If a pair of engines were drawing 1 amp of current, this would give a voltage drop of 8.5 volts at the end of the helix. This is quite significant and would definitely corrupt, if not kill, the DCC signal.

 I don’t think I was being overly cautious running a track buss along the helix.

George Booth
Director of Everything, The New Great Western Railway
http://users.frii.com/gbooth/Trains/index.htm

Artarms's picture

Three dimensional art

A model railroad helix has appeal because of its construction and its shape.  It shoud be in a sculpture collection.  If we were boy-scouts there would be a merit badge for helix building as it has to be one of the most difficult design and construction projects in the hobby.  Thanks for sharing.

Art Armstrong

Jurgen Kleylein's picture

I've built similar helices

Your method is very similar to one used on the Sudbury Division (we've tried several.)  Ours use half inch plywood as well, preferably poplar plywood.  Our vertical spacing is 3.5" per turn, no roadbed.  This allows us to get Walthers enclosed trilevels up with millimeters of clearance to spare--double stacks weren't invented yet in the 70's.  We used shorter laps, only about 1/2", since there's no benefit to making them longer.  The weakest point in the ramp on this sort of helix is at the beginning and end of each lap joint, where the wood is only half thickness; the plywood bends easily here, since it's only 1/4" thick.  We try to put spacer blocks above and below the joints to stablize them.  

One question, though:  why would you want to have superelevation on a helix?  That's the last thing I would want to do, since superelevation is purely cosmetic on a model railroad, and in fact makes it easier to stringline long trains on a curve.  We have one helix on our Soo branch which is 28 1/2" radius, and we manage to get 40 car trains up it.  If it was superelevated, I guarantee trains that size would tip over on it.  I've thought about putting a reverse superelevation (contra-elevation?) on a helix since that would actually help keep the cars on the track, but wasn't certain what that would do to coupler dynamics, so I haven't tried it so far.

Jurgen

HO Deutsche Bundesbahn circa 1970

Visit the HO Sudbury Division at www.wrmrc.ca

The preceding message may not conform to NMRA recommended practices.

Sugar Beet Guy's picture

Much ado about very little

I guess no one likes my helix wiring. 

I left out one aspect of the helix wiring because I didn't think it was of great interest. The power to the helix is split between two circuits.  The lower half of the helix is fed from the lower level track buss and the upper level is fed from the separate upper level track buss so the buss lengths involved are about 1/2 of what it appears.  

 

And the feed for the upper half is run vertically through the laps.

Back to the issue of voltage drop.  12 gauge solid copper has a resistance of 0.00187 ohms per foot. A 75 foot run would have 0.l4 ohms. With a 1 amp draw, the voltage drop is 0.14 volts. Or if you consider both conductors, 0.28 volts. I really don't see a problem with this. 

 

George Booth
Director of Everything, The New Great Western Railway
http://users.frii.com/gbooth/Trains/index.htm

LKandO's picture

I Have No Issues With Your Wiring

George, my comment was not that I didn't like how you wired your helix. My question was about the conductivity of nickel silver track. When I first saw your copper wiring following the helix spiral it made me think "Why did he do that when silver is a better electrical conductor than copper and nickel isn't far behind?" Then I followed the link to the video of the fellow showing voltage drop on his layout due to lack of feeders in his helix. This further confused me since by all normal standards nickel silver rail should be an excellent conductor given its composition and large cross section. I am anxious to do a bit of measuring myself but assuming all of this information is true then I can only come to the conclusion that nickel silver railroad rail must be chock full of impurities in its manufacture.

Table taken from CRC Handbook of Chemistry & Physics:

Resistance and Resistivity for Selected Common Metals

 

10-ga wire Resistance
Ohms/ft

Resistivity
10
-8 ohm-m @ 25º C

  Silver

0.000944

1.617

  Copper

0.000999

1.712

  Gold

0.00114  

2.255

  Aluminum

0.00164  

2.709

  Iridium

0.00306  

4.7    

  Brass

0.00406  

6.13  

  Nickel

0.00452  

7.12  

  Iron

0.00579  

9.87  

  Platinum

0.00579  

10.7     

  Steel

0.00684  

11.8     

  Lead

0.0127    

21.10   

 

 

Alan

All the details: www.LKOrailroad.com        Just the highlights: MRH blog

When I was a kid... no wait, I still do that. HO, 28x32, double deck, 1969, RailPro

Helix Types

 If it works for you, then your helix wiring is fine!

I have 3 helixes on my HO/HOn3 layout.  One is a "standard" one of about 5 turns in HOn3 only.  The other two actually are "stacks" of helixes.  One stack consists of a 1/2 turn dual gauge helix approached by a long grade. The second multiple turn helix in this stack is HOn3 only, with separate entry and exit points not related to the dual gauge one below.  It also is of smaller radius than the one below.  The third stack consists of a dual gauge helix twisting downward to a staging yard underneath the main yard, where the main entry is.  This main entry also leads to a single twist dual gauge helix on top of the lower one with the exit leading off to a long down grade.  This main entry also leads to a  third HOn3 only helix of several twists on top of the other two which leads to an HOn3 "high line".  All of these helixes are of the same radii.

All the helixes are built of 1/8" tempered Masonite laminated together with carpenter's glue and precut to various diameters.  This thinness is needed to minimize the grades.  All are supported by threaded rod material using washers and nuts, which allows fine tuning of the grades as needed.  To hold the track in place (all track in the helixes is ME flex track), I first tried glue which didn't work because of the plastic ties.  I ended up using AMI "Instant Roadbed" which both held the track firmly in place and deadened the sound.  The Instant Roadbed is  very flexible  and the plastic-tied flex track can be pressed into it, usually easily, depending upon e temperature of the room.  I have used a low wattage hair blower to soften the Instant Roadbed without softening the ties.

I assembled the roadbed, complete with the track and Instant Roadbed, before putting them in place on the layout.  That way, I could drill through the layers of Masonite and thus save time and make sure the holes were all aligned properly for the vertical threaded rods.  This helix setup has worked fine for the past ten years or so.

I use Digitraxx DCC and I ran the wiring busses but inside the edges of the helixes, following the turns, so the busses then could enter and exit the helixes at the proper places.  I elected to use horizontal power districts on the whole layout, rather than vertical ones, in order to make trouble shooting a lot easier because of the layout's various levels (there are 3) and geography.

AMI went out of the roadbed business in 2007, unfortunately.  The material is uncured butyl rubber and I understand that similar material can be gotten at auto supply stores that specialize in air conditioning parts (it's used to wrap a/c piping).  I haven't tried since I still have some AMI material left.  Somebody also found similar material at:

  http://www.trains.com/trccs/forums/1056223/ShowPost.aspx

Someone else has suggested trying plumbing supply stores; the material, or similar stuff, used to wrap pipes.

Hart Corbett

Novato, CA

 

 

 

 

 

Sugar Beet Guy's picture

Nickel silver has no silver in it!

According to various Internet sites, "nickel silver" is an alloy of copper, zinc, and nickel, often in the proportions 5:2:2. It does not contain silver.  You were lead astray by clever marketing
 
 
For a good explanation of wire and rail resistance, check out
 
 

George Booth
Director of Everything, The New Great Western Railway
http://users.frii.com/gbooth/Trains/index.htm


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