Decoder Install: Intermountain F3A

In this installment, we’re going to tackle another “easy” DCC decoder install.  Not quite as easy as the Kato NW2, but still very much a beginner project.  Today, we’re going to install a TCS IMF4 decoder into an Intermountain F3A locomotive.

This particular locomotive was a gift from a friend.  It’s an excellent runner, but happens to be missing a headlight.  We’ll discuss what to do about the headlight, and I will show its installation in another post as soon as the replacement arrives, but I won’t be able to show that step here.

You will need a soldering iron and solder, and you will need some insulating tape.  Kapton tape would be the better choice, but regular vinyl electrical tape is OK. Do not attempt this installation without a small piece of insulating tape.

OK, let’s get started, shall we?

Step 1: Remove the shell

The first step to remove the shell is to remove the front coupler.  Flip the locomotive upside-down, and remove the screw holding the coupler in place.  Put it somewhere safe!  Then pull the coupler straight out the hole in the pilot.  Store it somewhere safe as well.  You don’t have to remove the rear coupler.

Next, flip the engine upright and carefully lift the shell off the chassis.  Spread the sides apart a bit at the fuel tank with a pair of toothpicks.  Lift the cab end off first, and it will come off rather easily.

Step 2: Disconnect the LED

If your engine has a headlight (it should!), it will be nestled into the black tubing at the cab end of the loco, and two wires will extend back and be soldered to the light board where shown in the picture.  Take a note of which color wire is attached to which terminal on the board.  Better yet, take a photo so you can refer back to it.

With your soldering iron, melt the solder and disconnect the two wires.  Pull the wires back out of the way, but do not remove the headlight.  If you want to replace the headlight LED with, say, a different color or intensity, now would be a good time, though.

Step 3: Remove the light board

In the photo above, you’ll see that the light board is held in place by two screws.  Remove the screws (save them!!) and lift the light board out of the depression in the chassis.

Side Note:  Why you need insulating tape!

When I was preparing to do this install, a friend cautioned me that I would need some insulating tape.  He had learned “the hard way” by frying a decoder and taking advantage of the generous TCS no-questions-asked warranty.  From the install photos I had seen, I did not see why this would be necessary.  After all, wouldn’t the DC light board also need insulation?

Here’s why:  As you can see from the photo below, the back side of the light board (left) has no exposed circuit traces.  The board itself insulates the simple DC circuits from the frame.  The TCS decoder (right), however, has circuit traces and via holes (holes that provide an electrical connection between the two sides of the board).  These via holes would short to the frame if an insulator isn’t provided.

I am not certain why TCS does not provide a piece of insulating material to slip below the board, but it is definitely needed.  Kapton tape would be an excellent choice, but is relatively expensive and hard to find.  You can order it online from various sources (Grainger,, DigiKey, etc.).  Regular vinyl electrical tape will work, as would a carefully cut-to-fit piece of cardstock.

Step 4: Insulate the back side of the decoder

Before installing the decoder, you must insulate the back side from the frame.  Cut a piece of insulating tape to fit between the two posts for the motor brushes and the mounting screw hole on the far end.  The piece should be about 1/2″ wide by 1-7/16″ long.  It is OK if it wraps up around the sides a bit, but you must make sure it does not cover up the mounting hole in the corner nor the motor brush posts.  It must cover all of the other exposed metal on the back of the decoder board.

If you prefer, a thin piece of cardstock cut to fit under the board will work, but it must be thin enough not to interfere with the contact between the motor brush tabs and the posts on the decoder.

Step 5: Install the decoder and attach the LED

We’re almost done, but now you will need your soldering iron.

Before installing the decoder, slip another small piece of insulating onto the frame in the area where the LED wires will be – the cab end, that is…

Drop the decoder in place on top of the chassis and screw it in place.  Solder the headlight LED wires to the board on the two pads indicated in the picture (Note: the picture above is rotated relative to all the previous photos.  The cab end is to the right in this picture).  BE SURE to attach the wires in the same relative orientation as they were before you removed them from the light board.

Step 6: Reinstall the shell and front coupler

Slip the shell back over the chassis.  Then flip the engine over, re-insert the coupler through the front of the pilot and screw it to the chassis the same way it was before you started.

I found it helpful to slip a flat-head screwdriver between the coupler draft box and the front truck to help keep it square to the front of the locomotive while tightening the screw.  Otherwise the box will tend to turn with the screw, leading to a misaligned coupler.

And there you have it!  A DCC-powered Intermountain F3A.  The installation should be almost identical for the Digitrax DN163I1C, and also just the same for the F3B and F7A/B from Intermountain, all of which share a common chassis.



Decoder Install: Kato NW2

This should be a long post, but not too long.  We’re going to install a TCS K3D3 DCC decoder into a Kato NW2 N-scale locomotive.  The Kato NW2 was designed to be DCC-ready, and the TCS K3D3 is a drop-in design, so that makes this a very easy, 15 minute or less install.  If you have one of these nice little switchers, you should not fear this task at all.

This install procedure should also work for the Digitrax DN123K3, which is also a drop-in replacement for the Kato NW2, though I haven’t tried it myself.

Let’s get started, shall we?

Step 1: Remove the shell

The shell is basically press-fit over the chassis.  To remove, simply pull gently but firmly down on the trucks and it should slide off.  It may help to spread the shell just a bit with a toothpick on either side, but I can generally nurse mine off with some steady pressure.

Once the shell is removed,  you’ll be able to see the light board on top of the chassis, with the two tabs that connect the light board to the motor brushes (round things in the center of the chassis sides)

Step 2: Remove the motor clips

Next up, we need to carefully remove the motor clips.  These are the little metal things that look like frogs hanging from the light board with their legs wrapped around the motor brushes.  Before moving forward, study how the clip is attached to the light board and the motor brush.  Take a photo or two if it helps you.  You will reinstall the clip onto the DCC decoder exactly the way it is here.

To remove them, take a toothpick or a jeweler’s screwdriver (or tweezers) and gently pry the clip from around the brush.  Be careful, and don’t bend the clip out of shape, as you will need to replace it later.  The clip is springy, so it should pop off with some gentle pressure.  Once the “frog’s legs” are free of the motor brush, gently but firmly pry the clip from the light board and set it aside for use later.  Repeat on the other side.  The clips are identical, so don’t worry about getting them mixed up.

Step 3: Remove the light board

The light board is the circuit board on top of the chassis.  It is tightly held down by tabs in the top of the frame.  To remove, you must push it forward until it slides free of the tabs.  Squeezing gently on the bottom of the frame may help a bit.  Mine was very tight (a good thing), but with firm, steady pressure, it will slide forward and come loose.  I used a screwdriver blade as a pushing tool.  Probably not smart, as it may well have slipped and damaged the LED on the end of the board.  Better to use something a bit larger and more blunt, and less likely to slip.

Once you have slid the board free of the tabs, it can be lifted from the chassis and set aside.  I kept mine, but there’s not much reason to.

Step 4: Install the Decoder

To install the decoder, you simply place it on top of the chassis and slide it back under the tabs.  A couple of details, though.  The “body” of the TCS decoder is just slightly longer than the space between the tabs, so it won’t lay flat like the light board did.  To get around this, tip it up slightly and “tuck” it under the rear tabs just a bit, as shown above.  It will then lay flat and you can slide it into position.  It is a very tight fit (like the light board was), so you will have to press firmly to slide it into position.  Again, squeezing the bottom of the frame slightly seemed to help.  Finally, you can push the board in too far.  Try to align the clip contacts directly above the motor brushes so the clips will install easily.

Step 5: Reinstall the motor clips

Next we must reinstall the motor clips.  Press the clips directly onto the clip tabs, just like they were on the light board, and then snap the “frog’s legs” around the motor brushes.  Make sure everything is lined up straight, and you are almost finished.

Step 6: Reinstall the Shell

This actually turned out to be the trickiest part of the install.  For some reason, when removing the shell on my NW2, the cab detail part tends to drop out of position.  When that happens, the chassis won’t go back in exactly right, and it’s not immediately obvious why.  Here’s what the cab detail looks like from underneath when it’s loose…

And here’s what it looks like when it’s been pressed back into its correct location…

Double check this, and then slide the shell over the chassis until it snaps into place.  Congratulations!  You’ve just installed a DCC drop-in decoder in your Kato NW2!  You can now take it over to your programming track and customize it, or drop it on your layout and have fun!

This is a very simple install, about as easy as it gets.  If I weren’t stopping to take pictures and notes, and talking with two very excited kids, I could probably get it done in well under 10 minutes.  As it was, going very slowly with distractions it took 17 minutes total.  With this install, there’s no soldering, no wires, no insulating tape, no tricks at all, and you get a nice, smooth running loco “out of the box.”

If you’ve tried this install and have comments, questions, or ran into problems, feel free to share them here!

A new maintenance shack

  by BGTwinDad
a photo by BGTwinDad on Flickr.

This little shack will be a maintenance office/shed for the CH&FR MOW crews. It will be at the grade crossing just past the tail of the wye at Glover’s Bend (that is, it will be on my new diorama…)

This is my first kit build project… it is a GCLaser “West End Shack”. This little guy was surprisingly easy to assemble, though in hindsight there were a couple of details I wish now that I had painted first.

You can follow details of the construction on the thread I’ve posted at I still have to add some detail parts like the stove pipe, some electrical conduit, and the little fuel tank that sits outside.  This is a laser-cut microplywood kit, and it assembles quite easily for a structure so small.  Elmer’s carpenter’s glue (the yellow stuff) holds it all together, and the various features built into the parts help key everything so it assembles easily.  It is a slightly challenging kit for a rank beginner like me, but very buildable, as the fact that I didn’t completely ruin it will attest.

This shack should provide a nice place for the MOW crew to get in out of the weather, keep warm and dry, and handle the paperwork they need to do from time to time.

Locomotion, Part 1: Wheels on Rail

A recent online discussion spurred me to study in some depth just how a locomotive does its job… moving extremely heavy trains at speed.  I thought it would be useful to share an explanation of the science involved, and so here we begin a new series.

For this first installation, we will essentially ignore the difference between steam, electric, Diesel-electric, and even model vs. prototype engines and focus on what is happening between the wheel and the rail.

There are three basic forces at play:  inertia, friction, and the torque applied to the wheels by the motor.  Whoa! you say.  Big words in paragraph three!  Hold on, we’ll get there.

Inertia, you may recall from high school physics, is the tendency of a body at rest to stay at rest, or of a body in motion to stay in motion – in the same direction and at the same speed.  The locomotive must overcome the inertia of the train any time it wants to start, stop, or change the speed of the train.  For simplicity, we are lumping all of the drag forces on the train (wind resistance, bearing friction, etc. etc.) together under “inertia”, even though strictly speaking they are different things.  They all add up to “stuff trying to stop the train (or at least keep it from accelerating)” anyway.  We’ll dice out all those details in a later post.

Friction is the “gripping” force generated between two surfaces in contact with each other.  It is always directly opposed to a force trying to make the surfaces slide.  In our case, the friction is between the wheel and rail, and it is what allows the train to move.  The friction between the wheel and rail is called static friction because even though the wheel is rolling, the “contact patch” between the wheel and rail is not moving.  Once the force reaches the “traction” point – the limiting stating friction – the two surfaces will slip against each other.

Torque is the force applied to the wheel by the locomotive’s engine that tries to make the wheel turn and thus pull the train along.

The locomotive must apply enough torque to overcome the inertia of the train in order to move it, but if it applies too much torque, it will exceed the static friction limit, and the wheels will slip.  If the train’s inertia is higher than the static friction limit, the train is going nowhere, no matter how much torque is applied.  This can happen, for example, on wet or icy rails, or rails that are covered with leaves.  The rails are too slick, and the wheels cannot grip.

In short, one of three things is going to happen:

  • Not enough torque to overcome inertia:  train stalls
  • Enough torque to overcome inertia, but not so much we overcome the wheel/rail friction:  train moves!!
  • Too much torque: wheels slip.

In order to fix the first point – stall – we have little choice but to add more torque – either increase the throttle, or add more locomotives.  To fix the third, we must either reduce the throttle until the wheels stop slipping or do something – like dropping sand on the rails – to increase the friction so the wheels can grip.  Adding more engines can help, only to the extent that they increase the number of wheels (and locomotive weight) on the rail, and therefore increase the total traction (friction) available.

In the YouTube video posted above, you can see the effects of plenty of torque + too much drag + not enough wheel/rail friction.  It takes an hour of work to slowly get this coal train moving on the icy rails with no sand.

A practical example:  Yard goats with slugs.

Something puzzled me for a while… why in a yard, where engines are frequently starting and stopping and moving long cuts of cars around at very low speed, would you have a small, low horspower locmotive connected to a “slug”.  What’s a slug, you ask? A slug is a modified locomotive that has had its “prime mover” engine replaced with a hundred tons or so of concrete.  It usually is also missing a cab, and must be driven by a “real” locomotive.  It is merely an extra set of traction motors and a lot of extra weight.  Why on earth would we tax the poor Diesel under the hood of the main locomotive like this?

The above analysis gives the answer.  The engine and generator in even a small yard switcher can generate considerably more power (torque) than can actually be applied to the rails without causing wheel slip.  This extra power capacity is, essentially, wasted in a low-speed starting-and-stopping scenario.  By adding a slug, we provide eight extra contact points with the rails (assuming a 4-axle slug!), four more traction motors for converting the generator’s power to motion, and a pile of weight to create more friction on those eight extra contact points.

The slug allows us to direct the excess power capacity of the switcher’s engine/generator to the rails without creating too much torque at any given wheel.

Let’s put some (fictional and easy-math) numbers to this.  Let’s say the generator of a 4-axle yard switcher can create 8000 lb-ft total of torque.  Let’s also say that each wheel can apply only 500 lb-ft of torque without slipping on dry rail.  By itself, the switcher can only use 1/2 of its torque capability (500 * 8 = 4000 lb-ft) to the rails without slipping.  If we add a 4-axle slug, we add 8 more wheels (and 4 more traction motors) to the equation, allowing us to devote the full power of the generator (500 * 16 = 8000 lb-ft) to the job of starting the train.

We can see now how adding more weight and more wheels is a big asset when one is frequently starting and stopping trains.   But if the friction force is directly proportional to locomotive weight, why not simply make the engine heavier instead of adding the slug?  Good question.

In addition to the drag and friction and torque, we need to be mindful of the sheer weight on the rails – the loading gauge.  The rails (and the wheels!) can only support a certain maximum amount of weight at each wheel contact point without damaging them.  So there is an upper limit to the friction force at each wheel that is set by the strength of the rails (and the wheels too!).  To add more weight, we must spread that weight over more wheels.  Adding more wheels has the positive side effect of increasing the total contact patch area, which also increases the friction.

Note also that all of this applies to model trains as much as real ones, though it’s highly unlikely we will ever exceed the loading gauge of even N scale steel rails…

New Arrivals at Glover’s Bend

[flickr video=5489038248 show_info=true w=260 h=195]

Originally uploaded by BGTwinDad

Dateline Glover’s Bend, WV

The CH&FR Railroad, together with the Chestnut Hill Historical Preservation Society announced two new additions to their “living museum” collection: an Erie Lackawanna EMD F3A locomotive and a B&O/Chessie System bay-window caboose. Both were donated by an anonymous benefactor.

The locomotive, currently painted as Erie Lackawanna #6611, has a long history with the CH&FR. It was the first Diesel road locomotive purchased by the company all the way back in 1948. It served for several years in the Frost River area before being sold to the Erie Railroad. After a long service life and the eventual folding of Erie Lackawanna into the Conrail system, the engine was purchased by a collector in Ohio and carefully restored to operating condition.

The F3A, like many of the Historical Society properties, will be placed in revenue service on CH&FR lines, operating in the Glover’s Bend area on local freight runs and passenger excursions. Company and Museum officials are debating whether to keep the Erie Lackawanna paint scheme or to return it to its original CH&FR colors.

The F3 series are famous for being the locomotives that killed the steam engine in freight service, and remain among the highest-selling locomotives ever built by EMD.

The bay-window caboose is a prime example of its class, frequently used on the B&O and Chessie System during the mid 20th century. Due to some problems with the couplers and needed structural repairs, the car was dismounted from its trucks and brought into town on a flat car. Frost River Locomotive Works spokesman Earl Jacobs reports that the caboose will be ready for service in a few days.

In addition to the locomotive and caboose, the railroad acquired a 50-foot Berwick boxcar (built by Berwick Forge & Foundry of Berwick, PA) and a Pullman Standard PS2 2,893-cu.ft. covered hopper, the former in a C&O/Chessie blue scheme and the latter in a yellow B&O/Chessie scheme.