Thursday, November 26, 2020

Building a curved concrete bridge

In the next expansion of the layout I will need a bridge where the WP line again crosses the Humboldt River.  The bridge that is actually in that location on the prototype is a 4 section through truss bridge.  My bridge in going to have to be part of a curved section of track so I am going to use a ballasted deck, segmented concrete bridge.  I already have a straight version of this type of bridge that I installed on the Golconda section in February of 2017 and is featured in THIS POST.   For that bridge I had a couple of good prototype photos I was following.  This bridge is going to be more freelanced.  I had considered the BLMA kit which is similar to what I wanted but it was too short for my application so I decided to scratch build this one.

I started by making several bents using some of the poles from Rix Products highway bridge kits.  These are 1/8 inch in diameter so I am only using 3 per bent.  The horizontal beam is cut of pine strip with holes drilled into it for the poles so they are quite sturdy.


The curve is going to be 18 inch radius so using an 18 inch radius Tracksetta tool as a guide I marked out a curved section on a large sheet of .030 styrene sheet.  Then I cut the curve out with a pair of scissors.

.030 thick styrene was cut into five 20 x 17 n scale foot sections and glued onto the curved strip.  The outer edge has small gaps between the sections.  The excess of the original curved sheet of styrene was cut off at each end.   Then .060 x .060 L channel strip was glued along both edges to covers the gaps on the outer edge between the two sheets of .030 styrene. 

The longitudinal beams were made from 1/8 inch Plastruct square tube stock cut into lengths that matched that section along the edges.  To give the bridge deck some stiffness, short lengths of .040 music wire that had a slight bend were glued into the holes of the tube.

On the straight version of this type of bridge I had used 1/8 inch thick acrylic to make the bridge deck stiff but not being able to cut a curve in the acrylic I used 1/8 inch hard board.  Between the music wire joints between the beam sections and the hard board the bridge deck got quite stiff.

.040 x .060 styrene strip was added along the top near the edges of the deck to retain track ballast.  Bridge abutments of the correct height to match the adjoining sub roadbed plus the thickness of the cork were made from 1/4" plywood.   All the pieces were painted with Model Master aged concrete acrylic paint.

The bottoms of the poles were cut and angled to sit on top of 1/8" thick footings on the bottom.  The bridge is shown here set temporarily in place after all the parts were glued together and receiving some weathering.  Once more of the surrounding terrain is built up and the river get at least a basic finish then it can be permanently glued in.

Wednesday, November 18, 2020

Upgrading wheels on old Kato locomotives

I have quite a few of the older Kato SD40, SD45, U30C, and C30-7's and I really like them for their reliability and durability.  One thing that has bothered me is the way they would rumble through any of the code 55 turnouts that I have had on my last two layouts.   No such problems with code 80 like on the Ntrak layout or the staging yards of my current home layout.   Apparently the older releases of these models have what in the hobby are called "pizza cutter" wheels as they have a flange that is almost as deep as the rail code 55 rail is tall. 

So I decided to see if I could do something about this and found that Kato USA sells packages of 6 locomotive axles with low profile wheels so I order several sets of these.

Once I got the new wheel / axle sets I wanted to make a side by side measurements of all the dimensions of both new and stock.   My first impression of the new wheels is that they look more like railroad wheels.  I also noticed that they also appear to be the same or similar as what are on some of my newer Kato releases.   Below are two photos with the dimensions I measured on each type of wheel set.


The main difference between the two is that there is a .013 difference between the flange depth.  The old wheel flanges are actually slightly larger that the height of the code 55 rail which is .055 so no wonder the wheels bumped.  The wheel itself is .015 narrower than the stock wheels but since flanges on both are right on gauge I don't believe that would make any difference but it does look better.

To change the wheels the trucks needed to be removed and then opened up to expose the axles and gears.  Then those are popped out and the new ones popped in, they are a perfect fit.  It's a good idea to clean out the cups in the brass contact frames that the axle points go in before re-assembling the trucks.

It is an $8.00 investment in each locomotive but I feel it's worth it as they are otherwise such great runners and already have DCC decoders in them.  Little by little I plan to got through the fleet with this improvement.

Saturday, November 14, 2020

Yard sequencer

In previous posts I had mentioned the use of some automation in the staging yard, here is just a bit more detail about how that works.

I am using Aztrax IR sensors to sense when a train arrives on one of the four staging tracks.  The sending units are in stands made from brass while the receiving units are in the tracks between the ties.  These are positioned near the departing end of each staging track.

The post on one side of the stand is 1/8 inch hallow tube and the wires for the IR sending unit are fed down through it.  The post on the other side is 1/8 inch rod that has had the end threaded for 6-32 sized nut.  Before the IR sender LED's were installed, the stands were spray painted white.  After the IR sender LED's were installed white heat shrink tubing is slipped over after a hole is punched on one side for the sender.

Referring to the control panel photo and diagram below I will attempt to explain how this works.  When a train arrives at the IR sensor pair it triggers a one second closure of the relay on the Azatrax board. The relay contact outputs of the Azatrax units are wired in parallel with the push buttons on the control panel associated with the next track but first pass through a toggle switch labeled Auto / Manual in the photo.  In the auto position the contact will trigger the turnouts for the next track and the train on that track will leave.  In the Manual position that track will be skipped and the closure will go to the next track.   This allows the flexibility to use any of the tracks and skip others in the case there is no train on that track. 

In the photo below one of those IR sensors between the ties is pointed out.  This system has been working out fairly well.  I did have to move the sensors around a bit to allow for the arriving train to coast to a stop before reaching the end of the siding.   Also it does occasionally happen that the train stops with the sensors being right between the first and second locomotive.   If this happens then when that train goes out again, the second locomotive will be mistaken as an arriving train and cause the sequence to move to the next track.