Monthly Archives: November 2014

Changing Contact Adhesives

Unfortunately I had a fair number of other things to do this weekend, so I didn’t get as much done as I really would have liked.

Typically for attaching N scale roadbed and track, I use DAP’s Weldwood contact adhesive. What can I say – it’s cheap and it works.  However, the stuff is a witch’s brew of organic solvents that – in addition to potential biological side effects – features prominent warnings about causing an explosion when being used, say, ten feet from a furnace.  During the summer that’s not an issue, since the furnace is shut down dead (and I have an electric water heater, so that’s not a concern).  Since it’s now winter, ventilating the basement adequately to avoid the “big boom” isn’t as much an option.  So I set out in search of a better adhesive that would be less likely to form a mushroom cloud in eastern Colorado Springs.

What I found was 3M’s Fastbond 30NF.  It’s still a polychloroprene contact cement, but the chemical engineering wizards at 3M have figured out how to make it primarily water-based, rather than all the organic solvents in most other contact cement.  It’s explicitly marketed for its nonflammability when wet.  In fact, the datasheet shows that it has no flash point – you literally can’t ignite it.  Sure, it’s also rather expensive ($100/gallon), but less so than blowing up your house.

The good news is that it works, and works very well in terms of bond strength.  The bad news is that “Fastbond” doesn’t live up to the fast part of its name.  It has a significantly longer wet stage than the organic solvent-based stuff, which is understandable even in such a dry environment as a Colorado winter.  I found that I usually had to wait about 20-30 minutes between application and actually being able to adhere pieces together.

The good news is that my concerns about it not bonding strongly enough (because, somehow, I assume anything not based on hideously harmful and/or flammable chemicals is inferior) were completely baseless.  The 30NF bond strength seems significantly stronger than the Weldwood, up and to the point that I had to put spacers down to keep the track from accidentally sticking when I was assembling the rail joiners.  At least twice I had a tie stick down so hard it detached from the rail when trying to get it up.  As long as it endures over time (and I have no reason to think it won’t), this stuff is superior from a bond aspect.

The other downside, besides working time, is that any frothy or clumpy spot will dry white.  However, most of that will be under ballast, and you just have to be more careful to only apply a thin layer to the bottom of the track.  Really it’s just about learning to apply more carefully than the “slather it on” method used in the past.

What Day, What Year, What Season?

For many prototype and proto-freelance modellers, their layout is set in a specific month of a specific year, or perhaps even a specific day.  There’s absolutely nothing wrong with that, but I’m not that guy.  The CR&NW will take more of the approach that Eric Brooman took with his Utah Belt – time on the layout marches forward with reality.    Given that the basic reason for the line’s existence – copper ore hauling – won’t change substantially year-over-year, neither will my dedicated freight car fleet or motive power.  It does, however, allow me to adjust the interchange traffic and an occasional lease unit that will show up online, and vary the mix a little bit.  Rather than being in perfect lock-step with real time, I do think I’ll set it about three years in the past.  So, for example, 2014 in real life will be 2011 on the layout.  That allows me as an otherwise busy modeller time to ponder how the railroad would respond to real life FRA mandates, economic conditions, etc., and adjust things accordingly.

The one catch is that it will always be mid-September on my Copper River.  That’s because for years, it seemed as if I was always in Alaska in late August or September.  Alaska to me was always in the fall, and just jumped forward a year at a time between visits.  I love the colors of the trees that time of year, and the light is beautiful.  The rivers will still be running with a fair flow, but not raging full of sediment and debris and looking for all the world like a torrent of liquid concrete.  There’s no hint of snow yet at the elevations and regions modelled – only at worst maybe a heavy frost – though there may be some far up on the mountainsides.  The weather is still pleasant, but the menace of winter is looming.

I think how we’ll handle it is that we’ll start operating sessions in January with the model date being about September 7, and just let scale time march forward as it does.   I’m going to aim for getting a full 24-hour day in each op session, running the FC around 4:1, but I won’t know if that’s actually going to work out until I have a layout that can be operated and a few guys to try it out.  It may be that 4:1 is the right ratio, but we only run 12-18 scale hours at a time because everyone tires out after that.  In that case, we’ll just stop the clock when we get done and pick up from there at the next session.

It’s all very exciting to ponder, and quite frankly I really wish I could just snap my fingers and get all of the trackwork, scenery, and equipment ready to go, but there’s at least a year or two of work ahead of me before we’re even close.

Learning to Love the DIN Again

As many of you know from my previous post, I recently converted from Lenz to NCE, largely for the wireless throttles.  Despite that, I’m going to put in fascia cab bus jacks just in case.  While I don’t have any intentions of running the layout with wired throttles under normal conditions, I can foresee a day when it might be necessary.  The last thing I want is to have to cancel an op session because one of my neighbours cranked up their 900MHz cordless phone and took down the wireless throttles.

The one thing I don’t particularly care for with NCE is the use of 6p6c (often incorrectly called RJ11, RJ12, or RJ25) connectors for the cab cables.  You know, those little modular connectors commonly associated with phones.  And it’s not just NCE – everybody seems to have gone to these now.

Why don’t I like the 6p6c modular connectors?  I find the little plastic tabs hard to release from the jacks, that they often break after any significant use, and that wiring fatigue and failure often happens near the jack as a result of inadequate strain relief.  Just a month ago I was at an operating session and we had two different operators lose control of their trains because the cable failed right at the 6p6c connector.

It’s not (just) a personal dislike based on anecdotal evidence.  Often times manufacturers of 6p6c jacks don’t rate the number of insertion cycles, and those that do generally have minimum lifetimes in the 300-500 insertion range.  Modular jacks just weren’t designed to be plugged and unplugged repeatedly.  They were designed in 1975 by Bell to provide a cheap, uniform connector for telephone cords.  Telephones don’t get plugged and unplugged all that often, unlike a guy following his train around the room.

The good news is that there’s a superior connector out there.  The 5-pin DIN connector, standardized as DIN 41524, was designed originally for connections between audio equipment.  The connector itself has robust pins and can easily be moulded to a cable with an integral strain relief.  There’s no little plastic tab to break off.  Plus, even the cheapest jacks are rated for 1000+ insertion cycles, double or more what the RJs can handle.  I first encountered it years ago when I was using CTC-16e as my command control system, and I was pleased that Lenz had used it when I first moved to DCC.

NCE offered a dual DIN fascia panel at one time (the NCE UTP-DIN), but apparently they’re out of production and no longer available.  (Update:  I’m told via the NCE Yahoo group that they’re just out of stock, not necessarily discontinued as many of the retailers state.  Apparently Tony’s Train Exchange has placed an order for 500 of them and should have them soon.)  Lenz still offers the LA152, but they’re rather pricey ($25-35 typically) when they’re not out of stock. Apparently everybody else has decided they can live with the god-awful little RJ connectors.  I can’t.

As Usual, Build My Own

That left me with – as usual – only one option that I was happy with:  design and build my own.  Fortunately, the cab panels are extremely simple – just a couple jacks for the cab bus, a couple DIN connectors, some mechanical board-to-faceplate bits, and a “cab bus power” LED.

Building my own allowed me to make a couple improvements.  The biggest change from the NCE version is that these use 8p8c (RJ45) connectors for the cab bus that follow the NCE Cat5 pinout.  I also added a self-resetting polyfuse and a terminal block for injecting power into the cab bus, should it be needed, along with a jumper to select whether to inject power or just pass it along.  This replaces the 1/8″ audio plug on the back of an NCE panel where power can be injected, and adds a bit of protection (the polyfuse) against shorts.

Here’s a few pictures of the first assembled prototype, plugged into the CRNW’s cab bus a few hours ago:

As a ardent supporter of Open Source Hardware, this project will be released under a Creative Commons BY-SA 2.0 license, just like everything else I build personally.  (Yes, the board says Iowa Scaled Engineering, but given that I am half of ISE, I can do that…)  That license basically means that as long as you give me credit for it and you share any modifications you make likewise, you’re welcome to do whatever you want with the design.

For the prototypes, I’ve sourced the panels through a PCB prototyping service called OSH Park.  I use them for all sorts of things, and they do high quality work.  If you just want some v1.1 boards just as they are, you can order them directly via this link.  You’re also welcome to use the design files below to create your own gerbers and have them made through whomever you’d like.  The schematic and PCB are designed using the popular open source gEDA suite of design tools

Design Files and Bill of Materials

Schematic (PDF – v1.1 / SVN r1114)
PCB Images (PDF – v1.1 / SVN r1114)
Design Files (gschem/pcb – v1.1 / SVN r1114)
Faceplate CAD Drawing (DXF or PNG)
Faceplate CAM File (Cambam)

Bill of Materials
Digikey Part Refdes Qty Description
160-1940-ND D1 1 Yellow 3mm LED
RUSBF110CT-ND F1 1 1.1A Polyswitch (Note 1)
8190K-ND H1-H2 2 6-32 horizontal screw PCB mount
CP-2350-ND J1-J2 2 5-pin female DIN jack
151-1101-ND J3 1 Dual 8p8c jack
ED2609-ND J4 1 2-position 0.2" terminal block (Note 1)
3M9448-ND J5 1 3-position 0.1" male pin header (Note 2)
3M9580-ND none 1 0.1" shunting jumper (Note 2)
S1KQCT-ND R1 1 1k 1/4W 5% resistor

Notes:
Note 1: F1 and J4 may be omitted if you do not intend to inject power at this cab panel.  Also, see note 2.
Note 2: J5 and the shunting jumper that goes in it (part 3M9580-ND) may be omitted if you don’t want to ever change if a panel can inject power or not.  Just solder in a small piece of wire to permanently connect the proper two holes in the board.
Note 3: There’s nothing magical about most of these parts.  The Digikey part numbers are provided as a reference, but pretty much everything except the DIN plugs are commodity parts that can be found from many sources and from many suppliers.

 What About DIN Cables?

The other half of using DIN plugs in the cab fascia is that you have to actually have to have cables to connect them to the throttles.  The standard offering from NCE has a 90-degree plug at the end.  Again, while it should work with my panels, it’s not my favorite.  I’m also not a huge coiled cord guy – I find they often get all tangled up.

My solution was to purchase a 25′ male-male DIN cord from Amazon and cut it in half.  I then stripped the ends and crimped on a 6p4c connector to the appropriate wires.  It took a little doing to get the cable forced in far enough that the casing would engage with the strain relief, but it is possible.

At least for the cable I used, the pinout worked out as follows (your mileage may vary):

1 – no pin
2 – White
3 – Blue
4 – Green
5 – Red
6 – no pin

IMG_1139 My DIN throttle cable

 

The Electrical Cabinet Lives!

Work has been keeping me insanely busy lately, but I have gotten the start of the electrical cabinet installed.  So far, it’s mostly the three power supplies for the DCC boosters and the fourth power supply for the auxiliary power bus, the DCC system, and one set of DCC breakers, but it’s a start.  And it’s enough to power up the helix and Nizina, along with bringing up the programming track.

The wiring is still a bit messy, but that’ll get cleaned up before it’s final.  I just figure there’s no sense lacing things together before all the wires are in place.

electricalcab-5nov2014