DAWSON CREEK SUBDIVISION

RAILWAY PROTOTYPE MODELLING IN N SCALE

Timothy J. Horton

CONSTRUCTING THE HELIX

I have received many inquiries regarding the construction of my helix, and in response have presented a detailed overview here.

I designed an ultra thin sub-roadbed system for the 16" radius helix which uses 1/8" five ply birch aircraft plywood. The assembly is supported by six pairs of 1/4" threaded support rods. The sub-roadbed consists of a full width lower layer and an upper layer on either side of the trackbed. the lower and upper sections will overlap by 50 per cent, creating a roadbed which has ten plys yet is only 1/4" thick. This design provides the maximum amount of vertical clearance between turns.

These photographs show the roadbed pieces, which were cut on a laser cutter by Kevin Knox, the six pairs of 1/4" threaded support rods, and the associated hardware. The birch aircraft plywood was sourced from the United States, and the threaded rods and hardware came from the local Rona hardware store.

I used Elmer's Yellow Carpenter's Glue for assembly of the sub-roadbed pieces, and plastic clamps to hold the pieces in place while gluing. Any required cleanup of glue was accomplished with a paper towel and water. Drying time is about two hours so this was a project to keep coming back to at regular intervals. The parts overlap by 50 per cent so this first section had two half-length pieces for the top half.

The assembly process continued with the addition of adjacent sections, overlapping by 50 per cent, to complete a full circle for each turn. The laser cutting process ensured a high degree of accuracy with respect to fitting the parts together.

The holes for the threaded support rods were created during the laser cutting process to avoid having to drill them afterwards. Again, the laser process ensured precise alignment of the holes.

Following completion of the first turn, the assembly process was repeated for successive turns, which were left as separate assemblies at this stage. They would be added later upon installation of trackbed and track on the preceding turn.

This photograph illustrates all six and a half turns for the helix following completion assembly for the sub-roadbed. The assembly went very well due to the high quality of the wood and the precision of the laser cutting process.

I selected Woodland Scenics Foam Trackbed for my layout. The trackbed was glued in placed with Woodland Scenics Foam Tack Glue which proved easy to work with. Like the more traditional cork roadbed, the foam trackbed is installed in two halves.

The trackbed was glued into the centre depression around the turn. It is flush with the top surface of the sub-roadbed on either side, thus gaining an additional 1/8 inch of clearance between turns of the helix.

At the end of each turn, enough trackbed was left to cross the joint between turns.

I chose Peco Code 55 flex track for the helix as it is very strong and reliable, and generally holds its radius once curved.

The flex track was prepared for installation by forming it to the required radius of 16 inches. I used an acrylic template inside the curve to achieve the approximate radius, and then ran a 16" radius alignment gauge between the rails to correct any remaining gauge issues. A freight car was kept on hand to check performance on the track during this process.

Prior to laying track, the holes for the feeder wires must be marked and drilled through the sub-roadbed, and the feeder wires must be prepared and soldered to the underside of the track. The base of the rail and the end of the wire are tinned, brought together and heated to create the solder joint. Each section of track is fed at the centre, and also from the pair of rail joiners at each end for electrical redundancy and reliability.

Prior to gluing down the track, it is important to check to make sure that the track and attached feeder wires will fit in place and that the wires will pass easily through the holes. Each pair of feeder wires is also tested for electrical conductivity and testing.

The Woodland Scenics Foam Tack Glue is applied to the trackbed and spread into an even layer with my finger. Any excess or stray glue is easily cleaned up with water and a paper towel.

The section of track is then positioned with the feeder wires through the holes and is pressed down onto the trackbed and glue. The acrylic curve template is brought in to verify the correct curvature, and alignment gauges are inserted at either end to prevent the outward deflection of the rails which wants to occur there. The track was then clamped in place and left to dry for several hours.

This photograph shows tracklaying in progress on the first turn.

After installing the first three sections of track around the first turn of the helix, power was connected and a test train was operated to evaluate performance across the rail joints. The test train comprised cars of varying lengths.

This photograph shows the test train negotiating the first turn of the helix. This was actually the first train to be operated on a portion of the layout.

After several days of monitoring and testing the track around the first turn of the helix, I was satisfied with its performance and was ready to move onward and upwards. This photograph shows the second turn being added and clamped in place with clamps and Quick Grips. After the glue had dried, the foam trackbed and track were laid down across the joint and then extended around the new turn.

This process was repeated for each turn, always taking time to test each turn before adding the next.

This photograph shows the fifth turn being added to the fourth turn. Once again, clamps and Quick Grips are used to secure the joint, and various blocks are used to create space under the new turn in order to provide clearance for the clamps.

The remainder of the turns are collapsed upon each other at this stage of the assembly process.

This photograph shows the helix assembly after the attachment of all turns and the installation of all trackbed and track. The completed assembly comprises six and a half turns on a 16" radius.

An extension of flex track was left at each end to bridge the joints with adjacent roadbed. All of the feeder wires are in place and bent sideways below the roadbed.

Erection of the helix assembly went well. I began by installing the inner rods so that I could reach through to turn the nuts and washers. I then installed the outer rods. As each rod was added, the entire assembly began to firm up and straighten out. At this point the spacing is a rough estimate; the final adjustments were made after installation in the enclosure.

In this photograph I am installing one of the outer rods. All of the rods were inserted from the top down, and the nuts and washers were added as I passed through each turn.

This system allows for precise control of the distance between turns. Each turn can literally be dialed to the exact desired spacing simply by turning the nuts above and below the roadbed.

Some time after completion of my helix, I was shown a design refinement which is to insert a small wood block with a curved top in between the roadbed and the nut below. The curved top of the wood block allows the roadbed to rest upon it at the desired angle.

After an afternoon and evening of turning nuts and washers, the entire assembly was erected and roughly spaced out between levels. The extra length of rod at the bottom was used to anchor the assembly to the enclosure.

This photograph shows the Here is the completed and erected assembly, again with excess trackbed and track at each end to bridge the connection to adjacent roadbed once installed.

A magical moment arrived when, after so many months of designing and building the helix, it was finally time to run a test train all the way up!

In this photograph two Atlas/Kato RS-3s are hauling a fifteen car train up the helix. The two locomotives are retrofitted with NWSL low profile metal wheels and do not have traction tyres. They had no difficulty with the train, which will be a typical length for the Dawson Creek Switcher. At this point, DC power was fed only through a single connection to the rails.

This photograph is a close-up of the test train as it negotiates the helix, and is included to illustrate the design of the roadbed assembly and the clearance it offers above the train.

Trailers on flatcars will be the tallest equipment to be operated on the layout, so they were included in the test train. I also operated a test train with passenger cars to see how well longer equipment will fare, as I plan to have 85' and 89'-4" trailer flatcars in the future.

This photograph was taken from above the helix assembly and looking down into it as the test train makes its way up the grade.

At this point there were no concerns with the way the trains and the track were performing.

After further testing with different locomotives and rolling stock, the competed helix assembly was now ready for installation and permanent wiring.

While I was working to assemble the helix, my friend John Walter was building the enclosure for it offsite. After experimentation with a cardboard mock-up, John built the enclosure to my plans.

The enclosure was a tricky fit has it had to fit into the corner behind the entry door and mate with both the lower and upper deck benchwork.

This photograph shows the completed enclosure during a trial fit. This brought us to a moment of truth - would the completed helix fit inside the enclosure?

The next step was to lower the helix assembly into the enclosure and assess the fit. Here is a view looking down into the enclosure with the helix assembly in place.

The cleat in the upper left hand corner would support the adjoining sub-roadbed platform, and the shelf at the bottom would accommodate the DCC system components:. The hole in the shelf is for the power cords to pass through and down to the outlet below. Following this test fit, the helix enclosure was removed and taken away for exterior painting.

This photograph was taken after permanent installation of the helix. A single temporary connection to DC power at the bottom end was made, and the helix thus became the first operational part of the layout.

This photograph was taken from above and shows a test train negotiating the second turn on its way up the helix. The threaded rods can be seen anchored to the bottom of the enclosure, and the feeder wires are now waiting to be connected to bus wires.

This photograph shows the same train negotiating the sixth and final turn. The upper deck for Tremblay is seen in the distance.

The holes in the enclosure wall seen above the train were for the future passage of track bus wiring from the helix enclosure to the underside of the upper deck.

After several years of benchwork and lighting work, and the work to assemble and install the helix, trains were now moving on a portion of the layout.

The next step was to connect the trackage in the helix to the adjoining benchwork. There was a distance of 24 inches from the bottom of the helix to the tunnel portal where the tracks will emerge onto the lower deck. This section included a gap between power districts, a transition into the 2.33% gradient, and an easement into the 16" radius curve. This photograph shows the installation of the lower connection out to the Pine River bridge section.

This view of the interior of the helix shows the bus wires after installation. Each branch serves one turn and was terminated with a capacitor and resistor in series. (Please see the page on Control & Wiring for further details.)

The installation of bus wiring meant that power could now be fed directly to all sections of track in the helix, which improved electrical performance. The test train in the photograph is powered by the new direct feeds.

This final photograph shows a test train arriving at the upper end of the helix, and is included to show a close-up of the bus wires and the terminations. The bus wires were secured to the inside edges of the roadbed with small eyelets. This made it easier to solder the connections to the feeder wires while standing inside the helix.

The construction and installation of the helix was a major success for me and its subsequent years of trouble-free operation have validated the methods used.

As the top of the helix will one day be covered with scenery, I required a way for operators to be able to monitor the progress of their trains inside. My friend Mark Dance provided a detection circuit comprising LED emitters and detectors which would provide indication of passing trains on an indicator panel to be mounted on the fascia. This photograph shows the initial breadboard test, with the green LED indicating the boxcar's presence between emitter and detector.

The components for the Helix Occupancy Circuit included a power supply, LED emitters and detectors, LED indicator lights, the circuit board, and a lamicoid panel for the fascia which would house the indicator lights. An indicator light was provided for each turn.

My friend Doug Hicks simplified the circuit design and helped me to build it. This was my first experience with an electronics project and I quite enjoyed it.

The LED emitters and detectors were placed on opposite sides of the tracks facing each other in pairs on each level of the helix. They were mounted in metal brackets and the lead wires were brought down to the circuit board below the helix.

Here we see a train descending the helix and about to pass through the first pair of LED emitter and detector for Turn 6. This will cause an LED indicator to light up on he panel outside on the fascia.

This view shows a train finishing its descent of the helix and passing through the LED emitter and detector for Turn 1.

It also shows the lead wires routed down underneath the helix to the circuit board below. Terminal blocks were used to organize the wiring, and ferrules were used for the connections to the circuit board and terminal blocks. The result was a neat and tidy installation which has never given any trouble.

This photograph shows the Helix Occupancy Panel on the outside of the fascia. The green indicator light for Turn 1 is lit to indicate the presence of the train inside the helix seen in the previous photograph.

The panels mounted below the Helix Occupancy Panel are for the Ramp Meter (which indicates DCC current and voltage) and Power Management (which indicates the status of the circuit breakers and track power for each power district on the layout.