Fitting DCC to Wrenn OO Locomotives – Horizontal Motors

This week I’m going to share with you a simple way to add DCC (Digital Command Control) to older Wrenn OO locomotives.

Wrenn locomotives date back to the 1960s but don’t be fooled by their age.  They’re very good models and are still widely collected and run.  If you find one in its original box it may even be worth a lot of money, depending on the model inside.

One of their main advantages is they’re all metal, making them very heavy.  This gives them a lot of tractive effort compared to models produced in later years.  The mechanisms are simple but well-built which means most of them are probably still running well.  However these were all designed well before the concept of DCC came along so the motor wasn’t isolated from the chassis.  In fact one of the motor brushes is connected directly to the chassis which makes converting these to DCC a problem.

But to overcome that problem I’ve come up with a simple way to easily make the conversion.  The Wrenn locomotives I’ve come across have one of two types of motor; horizontal and vertical.  This week I’ll cover the horizontal motor which is in the 8F 2-8-0 as pictured bellow, the Castle 4-6-0 and the Rebuilt West Country 4-6-2 which is the locomotive I shall be working on today.

The Rebuilt West Country has the motor and all the wires located under the shell.

With the shell removed you can see a single black wire, which runs from the right hand wheels, connecting into the green wire and going to the right motor terminal.

The left terminal is connected to the chassis by a metal bolt.  Both terminals are linked by a capacitor which acts as a suppressor to prevent interference with televisions etc.  Each terminal also has a spring which keeps pressure on the motor brushes inside the brush holders.

The brush holder on the right is isolated from the chassis and is only connected to the green wire.  The brush holder on the left is the one which gives us the problem.  In the image below I’ve released the spring and the brush has fallen out.  Be carefull not to drop the brush as they are made from carbon, just like a pencil lead, and can easily crack.

The brush holder is made from brass and is fixed directly into the chassis, making a perfect electrical connection.  The brush holder should pull out with a pair of pliers as I have done below.  If not, it will need to be drilled out; if you have to do this dismantle the whole motor first, because you don’t want to damage the inside or get metal filings in the armature.

With the brush holder removed it’s a simple matter of replacing it with something which works as an insulator.  And the answer is a 3D printed brush holder.

These have been designed to be a direct replacement.  They are 3D printed in Shapeways’ Frosted Ultra Detail material and should fit into the hole with a push.  It’s important to check first that the brush slides freely inside the holder.  Any print residue inside may cause the brush to stick and this will prevent the locomotive from running.  Any residue can be removed with a drill, the same size as the brush, or a round file.  If the brush holder is a loose fit in the hole simply fix it in place with some superglue.  (Superglue is made from acrylic and so is the Shapeways FUD)

The black wire from the right hand side wheels has been cut and will be joined to the DCC decoder.  The capacitor has also been removed.  Under the left motor terminal is a bolt which also connects this side back to the chassis; this needs to be removed and left out.

At this stage a continuity test using a volt meter is a good idea to ensure the two terminals really are isolated from the chassis and both left and right wheels.  If they are, then the brush can be re-fitted and the spring clipped on to hold it in place.  The wires from the DCC decoder can now be soldered to the motor terminals.

The power feeds can now be connected; one goes to the black wire and the other to the chassis.  I connected the chassis wire to the screw holding on the weight at the front of the loco.

And that’s it, the loco is chipped and ready for testing.

Next week I’ll share with you how to isolate a vertical Wrenn motor and where to get the 3D printed brush mounts from.

OO Gauge Fixed Link Couplings – Part 2

Two weeks ago I started telling you about my OO Gauge Fixed Link Couplings, you can find the post here. In this week’s post I’m going to share with you the design and different types I’ll be making available and why.

As the name suggests these are fixed link couplings and can’t be uncoupled.  They’re designed to allow strings of rolling stock to be coupled permanently in sets with the correct-looking couplings.  This is ideal for exhibition layouts or block trains which don’t need to be shunted.

The two basic styles, as pictured below, are Instanter, shown in green and 3 link, shown in red.

The actual style of Instanter or 3 link is purely cosmetic as this simply forms a rigid fixed link between the NEM connection.  Why did I do this instead of leaving the chain links loose?  Well, if the links were loose it would alow the coupling to close up when a locomotive is pushing the rolling stock, but this would mean the loco will be pushing on the buffers. Unlike the real thing this doesn’t work very well on most ready-to-run OO rolling stock and tends to lead to derailment.  Having the chains fused turns the coupling into a drawbar and as it’s centered on the rolling stock it allows long trains to be pushed without any issues. To fuse the chain links I have drawn a bulge making them a bit fatter where the links meet; this causes them to overlap and become one solid piece.

As I said above, making the connection into a solid drawbar gives the advantage of allowing the train to be pushed but what about going around curves?  The NEM sockets do allow a bit of sideways movement but depending on which manufacturer will depend on how much. So I have designed in a flexible section at each end which allows for some more movement.  This can be seen on the Instanter connector below.

As the coupling bends either to the left or right one of the gaps will open slightly.  When the train is being pushed the gaps close equally keeping the force straight.

Below I have two brand new OO Bachmann covered hopper wagons linked with the coupling above.

As the trucks are twisted to the max, where the buffers touch, the NEM socket swivels as well as the flexible section in the coupling.

The different types, apart from Instanter and 3 link, refer to two variations in the NEM sockets.  The first is length, or rather the distance the NEM socket is set back from the front of the rolling stock.  Although the NEM standards specify the size and position of the socket, not all manufacturers have them in the same place. Length is also governed by the tightest radius curve on your layout.  The tighter the radius the further apart the rolling stock needs to be before the buffers lock and cause a derailment.  With some exhibition layouts which only have big radius curves my shortest couplings can be used.

The second is height, some NEM sockets are lower than others.  To solve this I did an in-depth survey of all the main manufactures and determined that the issue could be overcome with three different shapes, which are all shown below.

The top one is simply a straight coupling.  The second is a cranked coupling and the third is a step-up coupling.  Below you can see the same two Bachmann hopper wagons with a straight Instanter fitted.

The Bachmann NEM socket is low and consequently so is the coupling.  By using a step-up coupling it raises the Instanter.

The cranked coupling is designed to be used when connecting rolling stock from different manufactures.  For instance, below are a Hornby and a Bachmann coal wagons.  The Hornby NEM socket is higher than the Bachmann but using a cranked coupling solves the problem.

You many have also noticed the original plastic molded hook is still on the model above the coupling.  My couplings technically are still lower than the real thing but doing it this way means you don’t have to modify your rolling stock if you don’t want to as the new couplings simply plug-in.  I will also be offering an advanced range which raise the couplings to the corrected height but this will require the plastic molded hook to be cut off.

Next week I’ll share with you the full range of my OO Gauge Fixed Link Couplings as well as a way to judge which ones you need.

OO Gauge Fixed Link Couplings – Part 1

As promised in last week’s post, this week will be about 3D printed parts.  And these parts are OO Gauge couplings.

Traditionally OO gauge locomotives and rolling stock in the UK have relied on the hook and bar coupling or tension-lock shown below.  These date back to the Hornby Tri-ang era and although they work well they are rather unsightly and are in no way prototypical.

For many years different manufacturers trimmed and improved the design but there was no getting away from that huge hook and bar; otherwise their locomotives and rolling stock would not couple up to everybody elses.  Also there had to be a lot of gap between the couplings to allow trains to navigate very tight curves.  Starter sets and train sets always come with a tight loop of track and all the manufacturers wanted their trains to go around them.

Naturally exhibition layouts didn’t want this type of coupling and the modelers invented all sorts of ways to close couple and accurately represent the real couplings for their era. Many kits are now available but on older models a bit of cutting and drilling is normally required and this can get a bit tedious and expensive.

More recently the majority of manufactures have now standardised their couplings in that they have added a NEM pocket to the underside of their rolling stock.

A NEM pocket or socket, as pictured below, is a standard pocket which complies to NEM 362.  This stipulates the size and position of the socket.  The intention is that all rolling stock has a NEM socket which allows any type of coupler to be simply plugged in and will be at the right height.

Currently just about all OO stock now comes with a tension-lock coupling plunged into a NEM socket.

This now opens up the possibilities of getting correct couplings for your era.

Real modern UK rollings stock use the Bukeye connector which is the same design as the standard US equipment but this didn’t happen untill recently.  Early rolling stock was coupled by a 3 link chain and hook as shown below.

Each end of the wagon has a cast hook and a 3 link chain.  Therefore each end is universal and either chain could be lifted and dropped over the hook.  This simple method worked well but rolling stock snapped back and forth as the train accelerated and braked. The buffers are sprung as to absorb the impact but as the trains got heavier it became more of a problem so the Instanter coupling was invented.

This new coupling, as shown below, is similar to the 3 link but the central link is a special cast iron shape.

The coupling can still be used as a loose fit coupling or can be rotated to make it a close coupled connection.  To do this the wagon brake is applied and the locomotive pushed up which compresses the buffers.  Then the chain can be put over the hook and the center link easily rotated.  When the locomotive releases the pressure the buffers release but not all the way as the chain is now much shorter and pulls tight.  Because of the rounded shapes at the top of the Instanter it cannot rotate and keeps the link short.  Now the rolling stock is close coupled and will not snap back and forth.  In the drawing below you can see the Instanter in its rotated position with the rounded shapes at the top.

The two horns at the bottom of the Instanter are there to aid the shunter when they want to release or connect the coupling.  Once the locomotive has pushed up and compressed the buffers the shunter uses a shunter’s pole, as shown below, to hook the coupling up and over.  The metal ‘pigs tail’ in the pole hooks onto the horns.  This makes the shunter’s job safer as they don’t need to go between the rolling stock to couple up.

Many modelers are switching over to Kedee couplings, one of the American standard couplers, as they now supply a coupling which fits directly into the NEM pocket.

However these can be fairly expensive and what if you model older stock which would have had an Instanter or 3 link coupling?  Well the answer is a 3D printed couplings.

My design for these has evolved over the last few months and have been tested thoroughly.  Now I have a set which works in a variety of situations and in next week’s post I will tell you all about them and share with you some photos and videos of the real thing.

Adding Draw Bars to Yosemite Valley Railroad Log Cars

Back in 2013 I started drawing my Yosemite Valley Railroad log cars; you can read the original post here.  Since then I’ve built up a nice train of cars, however, I haven’t added couplings to them all.  So in this post I’ll share with you my simple and cheap design to complete the cars.

The original log car design, as pictured below, was intended to be used with Micro-Trains Z scale couplings.  These are compatible with N Scale couplings but are much smaller and look more prototypical.  However, they are very fiddly to assemble and, if you are doing lots of cars, can get rather expensive.  Also, if the coupling is slightly out of vertical alignment it can uncouple when the cars cross any bumps in the track.  As I only run my log cars in a fixed rake and don’t do any switching with them, installing the Z scale couplings on all the cars seemed a bit over the top.

Yosemite Bulk Head Log Car 2

To resolve this I have designed a draw bar to be used with the same mounting point. The Micro-Trains coupling box fixes to the cars with a screw; a pilot hole is printed in the underside of the car chassis to ensure the couplings are fitted in the right place.  My draw bars, as pictured below, are simply dogbone-shaped strips of 3D Printed Nylon.  This material is Shapeways’ White Strong & Flexible and I’ve used this as it’s both strong and cheap to produce.


Pictured below you can see the draw bars next to the log cars for a size comparison.


The draw bars will come in sets of eight on a sprue and can simply be twisted or cut off with a craft knife.


The holes in each end are the right size for a Micro-Trains screw, although you will need to shorten the screw and tap the hole in the car body.  Micro-Trains supply a tap set for this purpose which can be found on their website.  Alternatively I use tiny screws which are just about the right length.  I tend to get these from old CD drives and computer components which I’ve taken apart before throwing out. You will be amazed how many tiny screws you can accumulate like this.

Below you can see one of these screws in the draw bar, as it has a point it will tap the hole as you screw it in.


When the draw bar is fitted to the car the screw doesn’t want to be tight otherwise it won’t allow the draw bar to rotate.  I have fitted the draw bar under the bulk head end of the car, that way if the screw is too long then the excess length will poke up between the bulk head braces and will be hard to see.


The screw does need to be tight enough so when the car is on the rails the draw bar doesn’t drop as you can see below.


For the other end you could use another screw but this means the cars are permanently coupled together.  If you do a lot of exhibitions, like me, then this isn’t very practical.  So I use a short section of wire simply glued into the existing hole.  It needs to be a stiff, solid core wire, not a multi-strand.  This also means all the cars can only be coupled together facing the same way, just like the originals.


This wire then acts as a pin which will fit nicely into the hole in the end of the draw bar to couple the cars.


Lots of cars can be assembled in this way but the first and last car will still need a regular coupling on one end so locomotives and cabooses can be attached.


My test pieces have been printed in white simply because it’s the cheapest colour but these will be available in black as well.

I’m going to assemble a few more cars and run the set at my local club as a test before I release the draw bars for sale.  Logically there’s no reason why these couldn’t be used on any freight cars which have a body mounted coupling so I’ll try that as well and let you know how it works out.

Drawing a Dummy Chassis & Trucks for an N Scale Alco C-855 Part 2

As hinted at in last week’s post I’ve been working on the dummy chassis for the Alco C-855 and C-855B.  This week I’m going to share some of the progress with you.  You can read the first part here.

The actual chassis for the locomotive is a simple shape and as it fits inside the shell there’s no detail to add, with the exception of the air tank behind the fuel tank.  However, as this is normally hard to see I’m happy to 3D print the whole chassis in Shapeways’ White Strong & Flexible material.  This is a real bonus as, given the size of the chassis, it would be expensive in their Frosted Ultra Detail or Frosted Extreme Detail materials.  The WS&F is still very accurate which means the truck bolster pin holes will be in the right place as will the shell locating positions.

The trucks are very visible and in order to show as much detail as possible these have been designed to be 3D printed in the FUD or FXD which is currently the best quality 3D print material they offer.

In the last post about these trucks I showed you the first few steps which led to the basic truck and bolster pin connection being designed, as you can see in the image below.


Since then I have developed the span bolster connection between the two trucks.  Unlike the prototype, which had a solid bar connection from coupling to coupling, the model uses a bolster pin to connect the lead truck to the chassis and the second truck simply floats between the first truck and the fuel tank.  The powered chassis trucks, shown below, are made of several parts which screw together forming a permanent connection, which can swivel side to side and has some up and down movement.


3D printing has the advantage of being able to produce the two trucks as one piece while keeping the movement between them.  Below is a section taken through the trucks in which you can see their connection.  The truck on the left has a lug on the back with a slotted hole in the end.  The truck on the right has a slot in the cross member which the lug passes through.  It also has a pin which passes through the hole in the lug preventing the trucks from separating.  The two trucks are inseparable and to make this as one piece in any other way would be impossible.


Below is render of the front pair of trucks.

alco-c-855-dummy-truck-4The second truck has no bolster pin connection on top but I’ve left a level area to add a weight if required. The weight may be required if the truck lifts or bounces as the loco crosses turnouts.

At the rear of the second truck is a tail which fits into the gap in the chassis fuel tank.  When the trucks are fitted to the chassis with the bolster pin the tail will stop the trucks from rotating out, but will still allow the trucks to swing enough on corners.

At the front of the trucks is the coupling connection.  As with my other models I’ve added a pocket to accept a Micro-Trains body mount coupler.  The pocket is upside-down so the coupler drops in from the top and is fixed with the standard small screw.   This was done to maintain the strength of the pocket without adding extra material; if the coupling was fitted from below the coupling areas would be very bulky which is expensive and wouldn’t look right.  On either side of the coupling pocket I’ve added the walkway texture which forms part of the access steps to the front of the locomotive.  The rear set of trucks, as pictured below, doesn’t have this detail, nor does it have such a big pilot. The pilot is the area around the coupling.


The C-855B dummy chassis will have the rear set of trucks at each end as there aren’t any access steps at the ends of the B Unit.

With the designs complete the C-855 dummy chassis and trucks were sent to print and arrived looking very nice.


The chassis section, as it’s printed in WS&F, was ready to use right away, but the trucks needed their normal cleaning to remove the waxy residue left over from the print process.

The chassis was a prefect fit inside the shell.  With the powered chassis I designed a replacement fuel tank which fitted to the underside of the metal chassis as shown below.

Alco C-855 Fuel Tank Fitting 2 (render)

This fuel tank section had holes in the sides to locate the shell lugs.  The dummy chassis has these same holes so the shell clips on and can only be removed by spreading the shell.

The holes for the bolster pins had a bit of surplus material in them so I reamed them out with a drill bit which was roughly the same size as the hole.  Then I was able to fit the two sets of trucks, making sure the correct truck was at the front and the tails were in the fuel tank slots.

The Fox Valley wheel sets dropped in nicely to the trucks and then the dummy chassis was ready for some testing.


A UP heritage unit had the pleasure of pushing the dummy C-855 around our ‘Solent Summit’ layout this weekend at a running meet and it went very well.

I had put some weight inside the fuel tank area, as you can see below, and with the added weight of the metal wheels the dummy chassis tracked very well across turnouts and through bends.  I will probably add a bit more so when the weight of a large train is behind the locomotive it won’t try and roll as the train runs around corners.


I am going to make a slight change to the spacing of the trucks by changing the length of the connecting lug so it perfectly matches the Con-Cor trucks used on the power chassis; currently they are spaced slightly closer together and I may add a little bit more depth to the truck frames just so they look exactly the same.

The next thing for me to check is the coupling fitting and height which I will be doing next week but for now I aam very happy with the C-855 Dummy Chassis.


The design for this chassis, once complete, can easily be tweaked to fit the Con Cor U50 and Gas Turbine chassis and I’ll be sharing that with you soon.

Drawing a Dummy Chassis & Trucks for an N Scale EMD SD50 Part 2

In this week’s post I’ve got some follow-up pictures for my 3D printed N Scale SD50 dummy chassis.  Back in November 2016 I shared with you my designs for this project and you can read that post here.  Since then I’ve ordered the chassis and trucks as a test print, which came out very well, as you can see below.


The trucks fitted well and the chassis tracked well along the rails.


However, in my eagerness to test the parts I’d forgotten that the fuel tank on Atlas’ SD50 is not the same as their C-628; which I was using as a template model.  Consequently the SD50 fuel tank was much wider and had no way of fixing to the new chassis, as you can see below.


This was easily rectified by widening the chassis and creating the required fixing points, as you can see in the computer model below.


Although this made the chassis much wider I was able to remove the unnecessary material by adding the holes and slots in the sides and base. This keeps the cost roughly the same as before; Shapeways charge by volume of material for their 3D printing service. The chassis section was then 3D printed and now it looks like this:


Compared to the old chassis, as shown below, you can see the significant change which needed to be made.


I also made some other alterations to the chassis.  I added a direction indicator to one end to mark the front; this made sense as the chassis was very similar at each end which meant I kept putting it in backwards!

Also working with the original design I discovered it had a few weak spots which I was able to strengthen by adding stiffeners or simply thickening the material at that point.


The new chassis and trucks fitted perfectly into the locomotive shell and, although they still needed to be painted and weighted, the dummy loco ran perfectly round the layout with a powered C-630.


The coupling height is spot on but the fuel tank does seem to be very close to the railhead which could cause an issue when the loco crosses a transition to an incline.  However this is easily fixed by gluing the tank to the chassis.  The tolerance in the tank fixing allows it to drop, but when glued it will sit a bit higher.  In the 3D computer model I have lifted the tank fixing up a fraction to avoid this.


I still want to do a few more tests, add some weight to the chassis and paint it to make sure everything is correct before I release the model in my shop but that won’t take long. These trucks have been used on many locomotives so I’ll also be releasing them with different length chassis to fit different shells.  If you have a specific locomotive which you need a dummy chassis for, let me know and I can do that one first.

On another note, this wasn’t the only dummy chassis in my delivery from Shapeways.


This is the considerably larger dummy chassis for an Alco C-855 and I’ll be sharing this with you in a later post once I’ve had a chance to test it out properly, but so far it’s looking very good.