Drawing an Alco C-855 for N Scale Part 5

If you have been following my blog for a while you will know that I have been working on an N Scale Alco C-855.  You can read the first part here.  In this week”s post I will share with you what I have done to finish the A unit and get it ready to order a test print.

In my last post about the C-855 I showed you the first print of the metal chassis extenders and how I fitted them into the Con-Cor Turbine/U50 chassis.

C-855 Chassis Build 15

This chassis runs well, and pulls even more than in its original counterpart; probably due to the increased weight.  However there were a few issues with the print so I have improved the 3D model to rectify them.  In the image below you can see both parts from the top and bottom.

Alco C-855 Chassis Extenders mk2 (render)

The space for the motor has been widened by a fraction as the motor was a tight fit in the first print.  The wire channel has also been increased in size so the motor wire is a better fit.  I have also made some changes to the bottom of the lower section.  The arrows point forward on both parts to help with orientation when assembling the chassis.  There is now a rectangular nub that sticks out to locate the fuel tank on the bottom of the locomotive.  Also a square hole has been added which has been designed to take a 3D printed screw fixing which is used to hold on the fuel tank.  The exploded view below shows how these fit together.

Alco C-855 Fuel Tank Fitting 1 (render)

I have designed this assembly so the original Con-Cor turbine/U50 screw can be used athough any similar size screw will work.

Alco C-855 Fuel Tank Fitting 2 (render)

This section of the fuel tank is only the bottom as the sides are part of the main body.  Looking at the image above you can see a square hole in the side of the fuel tank, this is designed to receive a nub sticking out from the shell. You can see the nub in the image below which shows half of the shell.  As the bottom of the fuel tank is fixed with the screw it becomes a solid fixing for the shell.

Alco C-855 In Side Shell (Render)

As with a lot of ready-to-run locomotives, to remove the shell it can simply be spread in the middle and lifted off.

To make painting and adding decals to this model easier the four large sand boxes on the sides have been made as separate parts.  The rear six are the same but the front pair are longer as they have to step over parts of the chassis.  The shell has slotted fixings in the side of the running board to receive the sand boxes so they can be securely fitted.  The holes on the tops are handrail fixings.

Alco C-855 Sandboxes (render)

As with my DT6-6-2000 and RT-624 locomotives my C-855 will come with crew for the cab, Bert and Ernie.  The controls on the console are very basic but this is N scale so once they are inside the cab it will be hard to see anyway.

Alco C-855 Crew (Render)

Because of the shape of the chassis, there is a large chunk of metal sticking up into the cab, the crew had to be pushed to the sides.  There are locator pockets in the shell walls to receive the crew once they have been painted.  As the C-855s ran in an A-B-A configuration you may not want crew in the rear A unit so they can simply be left out.

Below you can see the crew in their place with half the shell removed.

Alco C-855 Inside cab (Render)

This view also shows you the headlight fitting in the roof of the cab.  The shell has been shaped to receive a standard 3v 2mm LED.  A nice warm white LED can be fitted directly into the roof of the cab and a pair of headlights will shine from the front.  This area will need to be painted black on the inside to prevent the light from shining through the shell.

Even the horn is a separate 3D printed part; this is both to make it easer to paint and to protect it from being knocked off in shipping.  Below you can see all the 3D printed plastic parts for one C-855.  The large gears are the drive shaft extenders which are needed when the chassis is extended.

Alco C-855 3D printed parts (render)

In the cab you can see lots of holes; this is because all the grab irons and handrails plus many other details are brass parts that will be supplied in a brass Additions set. The set will also include some of the metal walkways, windscreen wipers, side ladders, MU hoses and sun visors for the cab.

So putting this all together, this is how the N Scale C-855 will look.  Please note the trucks under the 3D model are not yet correct.

The end will have brass grab irons up the center and walkways over the air intakes.

Alco C-855 end (render)

The cab with all of its brass parts will be well detailed

Alco C-855 666.Front (render)

Overall this monster of a locomotive has an imposing presence.

Alco C-855 (Render)

The next step is to finish the drawings for the B unit and design a dummy chassis so an A-B-A set can be made without powering all the units, if required.

The new 3D printed metal parts as well as the 3D printed plastic parts for the C-855 have new been sent for test printing so I should have the first N Scale C-855 within the next few weeks.  Once it arrives and I have cleaned up all the parts I will share some images with you.

Converting An N Scale Bachmann F7 to DCC

The N Scale Bachmann F7 has had three revisions to date and the most recent one, made available in 2013, is supplied with DCC.  But what about the first two?  In this post I will show you how I add DCC to the locomotives in a cost-effective way.

The Bachamm F7 over all is not a bad locomotive; it has great polling power and the body work, although not as good as the Intermountain model, is nice.  They do tend to run a bit noisily so installing a sound decoder for me was not an option. As I have several of these, installing a basic decoder in each starts to add up, so again I am going to use one decoder to power two locomotives.  When doing this it is important that the locomotives run at similar speeds when used together on DC power.  Luckily these do, but if yours don’t I have already covered a topic like this and you can read about it here.

Bacmann F7 DCC Install 34

The F7 A & B set I am converting to DCC, as shown above, is the second version but both first ‘Plus’ version and the second ‘Spectrum’ version are very similar in chassis shape and design so this method will work for both.  You can read about the difference in Spookshows N Scale encyclopedia here.

With the shells removed, as you can see below, both the A and B units are exactly the same with the exception of the A unit having a light bulb pushed into the hole at the front.  To remove the shells simply spread them at the fuel tank and they will un clip then lift off.  You will also see that the chassis totally fills the A unit shell leaving no room for a DCC decoder to be installed.  But because the B unit has the same chassis there is space in the B unit where the cab would have been so I will be putting my decoder there.

Bacmann F7 DCC Install 1

There are no wires inside the chassis, which is split into two, and the light bulb simply picks up power by touching the chassis halves.  A down side to this when running on DC is the light comes on in reverse as well.  And for DCC,  the motor picks up its power in the same way so we will need to isolate it.

To take the chassis apart is fairly simple.  First remove the fuel tank by undoing the screw in the middle.

Bacmann F7 DCC Install 2

Then undo the two chassis screws in the left half and it will lift off.

Bacmann F7 DCC Install 3

Turning the left half over you will see a spring projecting out of the chassis.  This is the bottom motor contact that connects the left half to the motor.  This spring needs to be removed simply by pulling it out.

Bacmann F7 DCC Install 4

With the two halves separated the whole assembly will come apart.  The motor simply lifts out and the truck assemblies will already be free.

Bacmann F7 DCC Install 5

The right half of the chassis has a stub that sticks out and connects to the top motor contact.

Bacmann F7 DCC Install 37

This stub needs to be removed.  This can done with a good pair of large side snips and a file.  The chassis is made from a fairly soft metal so it files down quickly.  In the photo above you will also see the inside of the black tape that has been put across the holes in the chassis. I believe Bachamnn added this to the second version to prevent particles getting into the motor winding.  Also as it is sticky on the inside it will catch any particles thrown off the motor brushes.  You can see some of those just below the stub. Filling the stub will create metal fillings which you also don’t want to get in your motor so once the stub has gone remove the black tape and clean the chassis half to remove all the filings.  A stiff brush will normaly do this.

With the chassis half clean, you can do a test fit with the motor to make sure the motor contacts to not touch the chassis.

Bacmann F7 DCC Install 6

To do a proper test the chassis can be resembled with just the motor in it and you can do a continuity test with a volt meter.  Dont forget to put the little plastic spacers back in, there is one for each screw and one in the fuel tank.

Bacmann F7 DCC Install 7

Next we need to create a path for the bottom motor wire.  As there is no room inside, the wire will have to come up the outside of the chassis but as the shell is a snug fit around the motor, there is still no room.

Bacmann F7 DCC Install 8

So in order to make room I have filled a V grove up the side of the right chassis half.

Bacmann F7 DCC Install 9

The grove also continues round under the fuel tank.  The grove needs to be just big enough to take the wire you are using so the face of the chassis and wire will be flush.

Bacmann F7 DCC Install 10

Once any metal fillings have been removed the chassis is now ready and we can turn our attention to the motor.  The motor body is already isolated from the contacts so all we need to do is add our wires to the contacts.  Although we can change this later it is useful to add the right wires onto the motor now so we know which is the positive side.  Normally orange is the positive motor wire and gray is the negative.  But there is no indication on the motor as to which is which.  On my work bench I have a DC controller with a test track and a pair of wires.  When a train is running forwards and to the left the right rail is my positive, colored red, and the left is my negative, colored back.  Touching the red and black wires onto the contacts will make the motor spin and in the configuration shown below you want the motor to spin anticlockwise.  That would be the same as forwards to the left.

Bacmann F7 DCC Install 11

To add the wires I quickly heat the contacts with the soldering iron, for one to two seconds, then add a little bit of solder just to tin the contact. You don’t want to over heat the contact is it is a perfect conductor of heat and there are plastic parts inside. Next I tin the end of my wire, hold it to the contact and quickly touch it with the iron.  The two tinned areas fuse and you have a good connection.  Note the wires need to be long enough to run up inside the locomotive and across to the B unit.

Bacmann F7 DCC Install 12

Before re-assembling the chassis I also change the couplings on the loco.   When these where being run under DC I used Unimate couplings from Red Caboose.  These provide a nice close couple that will not come undone on the track however as I will now have wires running between my locos I don’t want them to come uncoupled at all.  To do this I will replace the Unimates between the A and B unit with one of my fixed link couplings.

In the image below you can see the underside of the Bachamnn power truck.  Just to the right of the tuck and before the coupling box are a pair of pins that can be squeezed together with a pair of needle nose tweezers.  This will cause the coupler box to pop off.

Bacmann F7 DCC Install 13

Inside the coupler box is a spring that fixes over the peg on the back of the coupler.

Bacmann F7 DCC Install 14

My 3D printed fixed coupler is a direct replacement for the old Rapido style couplers so drops right into the Bachmann coupler box.

Bacmann F7 DCC Install 15

For now I only fixed one truck to the fixed link but you could do two, one from the A unit and one from the B unit, at this point.

Bacmann F7 DCC Install 16

Now the chassis can be reassembled.  Note the wire form the bottom motor contact is coming out the bottom of the chassis in front of the plastic spacer. (I know the wire is brown and not gray but I have run out of gray!).  Also when you refit the tracks make sure the metal contact for power pickup is rubbing against the underside of the chassis not the inside as this will prevent the trucks from rotating.

Bacmann F7 DCC Install 17

The brown wire (bottom motor connection) can now be placed in V grove that was filed earlier and the fuel tank can be replaced.  Also I have put some Kapton Tape over the holes in the chassis to replace the black tape I removed, this also holds the wire in place.

Bacmann F7 DCC Install 18

Now the motor is isolated and wired up the next two wires are the power supply.  On top of the chassis are four nubs that the shell sits onto.  Interstingly these are slightly narrower on the bottom than they are on the top so all I do is wrap the end if my wire around the base of the nub a full 180° and solder it in place.  I have yet to have one of these fail.  And as long as there is nothing sticking up above the top of the nub the shell will still fit.  The red wire goes to the right side and the black, or purple in my case, goes to the left.  I must order some more different colored wire!

Bacmann F7 DCC Install 23

The last wires, for the A unit, are for the light.  The standard light is a light bulb and these can be power-hungry and get hot.  So I replace mine with warm white LEDs. Below is a comparison with standard 3mm LED on the right and a 1.8mm LED on the left which I will be using.

Bacmann F7 DCC Install 19

As all LEDs need a resistor in line I make the resistor a part of the headlight by folding one of the resistor legs back onto its self and soldering it to the LED.

Bacmann F7 DCC Install 20

Then I wrap it all in Kapton Tape to prevent it shorting.

Bacmann F7 DCC Install 21

Finally I trim back the legs ready to solder on the wires.

Bacmann F7 DCC Install 22

The LED will sit in the same place as the light bulb.  To protect against shorts I put a strip of Kapton Tape over the nose then cut out the hole with a sharp knife.

Bacmann F7 DCC Install 24

The LED light assembly then pushes into the hole and the legs, sitting on top of the Kapton Tape, can be soldered too.  As LEDs only work in one direction it is important to know which is the positive and negative.  The blue wire, matching the decoder, is the positive.

Bacmann F7 DCC Install 25

With all the wires in place they can now be taped down with Kapton Tape so they are tidy and clear of the shell.  Check to make sure the trucks rotate freely.

Bacmann F7 DCC Install 26

To fit the shell I you could simply run the wires through the window in the connecting door at the back but this can be really tricky so using a sharp knife I simply remove the plastic under the window.

Bacmann F7 DCC Install 27

This allows the shell to be lowered onto the chassis without pulling or pushing on the wires.

Bacmann F7 DCC Install 28

When it comes to the B unit I do exactly the same, except the wires run to the front and there is no light.

Bacmann F7 DCC Install 29

To join all the wires up I like to uses little bits of cooper strip board.

Bacmann F7 DCC Install 30

These are then superglued to the nose of the B unit.  You could use one piece and glue it to both sides of the chassis but this would mean the unit could not be taken apart for repair if needed.  You also need to make sure the DCC decoder will fit behind the cooper strip boards and they do not protrude out side of the chassis so the shell will still fit.

Bacmann F7 DCC Install 31

Once you are happy with the placement of the cooper strip board, solder the wires together, orange to orange etc. The red and purple (black) can go directly onto the B unit chassis.  At this stage there are a few checks that you should make.  First, using a volt meter set to a continuity check, check that the left B unit chassis is connected to the left A Unit chassis, and repeat for the right.  Secondly check that the left and right chassis are not connected to each other.  Thirdly check that none of the chassis are connected to any of the cooper strip board terminals.  Then using 12v DC wires from a controller test that both motors are running the same direction when you connect them to the orange and brown (gray) wires and finally test the headlight works when you connect the 12v DC wires to the blue and white wires.

Bacmann F7 DCC Install 32

I also connected the fixed link coupler to the front truck of the B unit at this stage.

The last stage is to solder the six decoder wires to the copper strip board terminals and chassis points.  I have used a Digitrax DN163, it was a bit of a tight fit because this decoder has a plug on it making it thicker than normal but most N or Z scale decoders will fit.

Bacmann F7 DCC Install 33

I cut the front door of the B unit shell to fit over the wires the same as I did with the A unit and fitted it onto the chassis.  And there you go; two powered locomotives connected with a draw bar, which is prototypical, and one decoder.

Bacmann F7 DCC Install 35

But there is one more thing that you can do to make this even better and that is to have four locomotives with two decoders.

Bacmann F7 DCC Install 36 Normally the locomotives would all have different numbers but to make things easy I have configured the two DCC decoders to be both the same address and switched the rear pair to run in reverse as their forward direction.  This means you don’t have to consist the locomotives, and they won’t take up two slots in your DCC command station. This can all be done by changing the configuration variables or CV values; which can be fairly in-depth subject so it is something I will cover in a later post.

Re-powering A Dapol Semaphore Signal

Recently I have been working on a British outline OO layout which had some working semaphore signals.  Sadly some of these signals had suffered some electrical damage which rendered their control circuit boards inoperative. In this post I will be sharing with you a few simple methods of repairing Dapol semaphore signals.

The Dapol semaphores, as shown below, are nice looking signals and have a fairly basic drive system which is self contained in the tube below the signal.  Above ground there is a nicely detailed rectangular post with the rotating arm on top.  The arm is connected via a crank to a push-rod that runs down behind the post.  You will be able to see this in some later photos.  The glass lenses in the end of the arm are transparent and a small LED shines through creating the correct color.

Dapol Signals 1

Below ground is where all the clever parts are.  Interestingly the drive system on these OO signals is also used for their N Scale signals; Dapol have simply changed the size of the signal on top.  In the large threaded tube at the bottom of the signal is a circuit board, electric motor, gear rack and worm gear.  After the large nut has been removed there is a tiny screw at the base of the signal which holds the two halves of the tube together.  Once that has been removed the tube can be separated.

Dapol Signals 2

The motor is in the left half and the circuit board is in the right.  You can also see the push-rod that runs up behind the signal pole in front of the ladder.  And if we zoom in you can see below the push-rod is a spring.  This spring is attached to the push-rod and when it’s moved up and down the signal arm moves up and down.

Dapol Signals 14

The two pairs of metal contacts are part of the circuit board; as the motor spins the worm gear it drives the rack either up or down pushing the rod.  A spigot sticking out of the rack touches one of the pairs of contacts creating a circuit and telling the circuit board that the rack is at the end of its travel.  However as the circuit board is damaged these are of no concern to us.

As new, the signals work by providing 16v AC power to the red and black wires.  This powers the circuit board and the LED at the top of the signal pole.  Then by simply touching the two yellow wires together, using a momentary Push-To-Make switch, the signal will change. Even when you let go of the switch the motor will keep going untill the rack gets to the end of its travel.

On the first of the two damaged signals only the motor drive function was inoperable, the light still worked when 16v AC power was applied, so the circuit board was still producing low voltage DC which is also needed to drive the motor.  In the picture below you can see the wire connections.  The red and blue are the DC feed to the motor.  The tiny red and, hard to see just above the yellow, tiny black are the LED feed that run up inside the signal pole.  The big red and black are the 16v AC power in and the yellows are the activators.

Dapol Signals 4

So to fix this signal I removed the motor wires from the circuit board and extended them by soldering on some more wire and heat shrinking the joint.

Dapol Signals 5

Then I removed the yellow activator wires from the circuit board and added a pair of wires to the LED feed connection points.

Dapol Signals 6

The signal was then reassembled with the new wires coming out of the bottom.

The next step was to take the low voltage DC power, coming from the new blue and green wires, out to the layout control panel. Then, using a momentary double pole double throw (DPDT) switch, return the power to the motor wires, in positive or negative, to make the motor go one way or the other. The DPDT switches I use are toggle switches as shown below.

Dapol Signals 16

These have six connections on the bottom.  When it is thrown one way it joins the middle pair to the top pair and the other way joins the middle pair to the bottom pair.

So, if the incoming low voltage DC power is connected to the bottom pair, then reversed and connected to the top pair, throwing the switch one way or the other will reverse the DC power.

Dapol Signals 15

The motor is then connected to the middle pair of terminals, not shown above, and the signal can be manually controlled. My apologies as I got a bit carried away with the work and so didn’t take any more photos of this particular signal.  As the switch is a momentary, when you let go it springs back to the middle and stops the motor.  There’s no danger of pushing the motor too far as when the rack gets to the end of its travel it simply stops, although the motor keeps spinning.  The spring on the end of the push-rod, and there is another one on the bottom of the rack, supply just enough pressure to make the rack re-engage with the worm gear when you want it to run the other way.

This fix, although functional, is not ideal as you are still relying on a damaged circuit board and all the small parts inside the tube.  Plus you have to hold the switch untill the signal has reached its position.

The second fix I have for these signals is a bit moire drastic but I think in the long run is a more durable solution.

The second signal’s motor and circuit board had failed so I removed all of the parts from inside the tube.  Sadly the LED had also blown on this particular signal so the wires for that will go as well.

Dapol Signals 7

As all the points on this layout are powered with Seep point motors it made sense to power the signal in the same way.  Seep make a special point motor with a latching spring which is designed to work with hand-built points that don’t have a latching spring of their own.  The latching spring means the motor will stay in the required position even though the spring on the push-rod will be pushing back.  This latching point motor was mounted to a ‘Tee’ shaped mount as shown below.

Dapol Signals 8

There is a slot for the motor throw bar to pass through and the large hole above the throw bar is for the signal tube.

Dapol Signals 9

You can see the latching spring under the motor cross-bar.

Dapol Signals 11

As the tube on the bottom of the signal was now empty it could be reduced in length; this was also necessary so it didn’t hit the throw bar.  The last thing to do was to connect the throw bar to the signal push-rod.  However there is a problem in that the point motor movement is more than the signal needs, and as the point motors are powered by Capacitor Discharge Units the motor bangs over very hard which will damage the signal.

To counteract this I made a very basic omega ring out of thin nickel rod.  One end was superglued into the spring on the bottom of the push-rod, the other was looped around the motor throw bar.

Dapol Signals 13

Although basic, this omega ring absorbs the sudden shock from the point motor as well as any extra movement while still supplying enough force to move the push-rod.  The two shorter tube halves were glued together and the ‘Tee’ mount was screwed to the underside of the layout.  The signal was then put though the hole in the layout and mount.  Before the large nut was tightened up the signal could be tilted to one side to alow the omega ring end to be slid over the point motor throw bar. Once tightened up the omega ring could not slide off the throw bar, but as an extra measure I glued a small washer onto the end of the rod.

This second fix was a lot better because the signal changed quickly with a single touch of the switch and any wiring is the same as a standard point motor.

These signals have also been modified in a similar way with servo motors which gave a very nice smooth action and this might be something I will try next time.  If I do I will share it with you.

New Gears for an O Scale Rivarossi F9 Revisited

Back in February of 2015 I shared with you my 3D printed replacement gears for the Rivarossi O Gauge F9, you can read the post here.  Since producing the gears we have picked up a few anomalies in the different Rivarossi locomotives, mainly caused by a large manufacturing tolerance, that causes an issue with the gears.  In this post I will be showing you the new updated gears.

Although the 3D printed gears are vertically identical to the original Rivarossi ones they have been coming out at about 0.3mm to 0.5mm larger in diameter than anticipated.  For the majority of the Rivarossi O Gauge F9s that were fitted with the new gears, this had no impact as there was room for this.  But a few seemed to bind up.  The problem was traced to the 3D printed gear teeth hitting the corresponding gears root.  The root is the bottom of the gap between the gear teeth.

To solve this the 3D printed gears teeth where reduced in length by a fraction each reducing the overall diameter of the gear.

Below is an image with all three gears.  On the left is one of the first run of 3D print gears, in the middle is the original injection molded gear and on the right is the new 3D printed gear.

Rivarossi o Scale Gears 1

Although it is hard to see, as the difference is small, the teeth on the new gear are slightly shorter than on the first run.  This will make the new gears mesh perfectly with all the existing Rivarossi gears even if the drive gear position is a bit out of tolerance thus eliminating the problem that arose with a few models.

All the gear pack in my shop have been updated to the new versions and you can get them here.

Mike Dobson is the fellow modeler who first asked me to 3D print the gears to repair his locomotives and below you can see the new gears fitted to a chassis under a Great Northern GP7 shell.

Rivarossi F9 (O Scale Gears 6 (Mike Dobson)

As you can see below Mike has several sets of axles already repaired with the new gears ready to be fitted to his locos.

Rivarossi F9 (O Scale Gears 7 (Mike Dobson)

Rivarossi F9 (O Scale Gears 8 (Mike Dobson)

With the locomotive reassembled, it was time for a test run.  Mike storage yard is above his layout in the roof and there is a fair climb up to it.  This is a great test for the gears.

Rivarossi F9 (O Scale Gears 9 (Mike Dobson)

And finally we have a video of his repaired GN GP7 running on Mike’s layout.

And that ‘wraps up’ my last post before Christmas, but not wanting to leave you with out a gift, the nice people at Shapeways are having 15 days of deals to close out 2015, and today’s deal is $10 off all Frosted Detail Plastic orders of $30 or more!  As all the gears and my locomotive shells and detail parts are printed in Frosted Detail Plastics this could be useful.  Simply enter the code FROSTY2015 at the checkout.  This offer ends at 11:59PM Pacific Time on the 21 December 2015.

Happy Christmas

Adding N Scale Wheelset Resistors for Circuit Detection

As well as 3D printed models I do a lot with DCC and model railroad wiring.  Recently I have been building computer controlled DCC layout and this adds a whole new level of requirements to the layout such as circuit detection.  In this post I will share with you how I get rolling stock ready for circuit detection on an N Scale DCC layout.

Circuit detection is fundamental to computer control as it tells the computer where trains are on the layout.  It is also useful if you have hidden sidings and you want to know where your trains are.  There are several companies that produce circuit boards for circuit detection and on this layout I have used Digitrax’s BDL168 boards.  The boards work by measuring a resistance across the track; this can be anything from an LED to a DCC chipped locomotive.  So if you have a locomotive in a section connected to a BDL168, even though it’s not moving, the board will detect a resistance and turn on the output for the section.  The output could be connected to a display panel or a computer could pick it up through the Digitrax Loconet system.

This is fine for locomotives and rolling stock with illumination but what about basic freight cars or wagons?  The computer controlled layout I’m building is a British outline model railway and has a lot of coaches that will all need to be modified so the circuit detection can pick them up.  A lot of the coaches, as shown below, are made by Graham Farish and luckily have metal wheels, obviously plastic wheels sets are no good for circuit detection..

Wheel Set Resistor 1

If you do have rolling stock with plastic wheels you can get replacement wheel sets for just about all ready-to-run stock.  Although metal wheels usually run better you don’t have to change all the wheel sets for metal ones, only the ones you intend to modify.  In fact you only need to modify one wheel set per item of rolling stock.  Because of the length of the coach I am going to modify one wheel set in each truck.  If it was a short wagon I would only do one.  Ideally I would like to modify the two outer wheel sets but as the axle is so close to the coupling box there would be no room.

Wheel Set Resistor 2

Adding lighting to the coach would be one way of creating a resistance across the coach but by far the simplest way is to add a resistor to a wheel set.

Wheel Set Resistor 13

As you can see from the images above with N Scale, and OO/HO, a standard resistor is a bit big and would be very impractical.

To overcome this, tiny resistors called ‘Chip Resistors’ are available, and are also very cheap to buy.

The best size of resistor for this job is a 10K Ohm.  The Ohm rating is the measurement of resistance and it is important to get this correct as the wrong resistor may cause heat which might warm up the wheel set and melt your train.  The chip resistors are usually supplied in strips as shown below.

Wheel Set Resistor 3

Close up you can see the tiny chip resistor, each one is in a pocket in the strip and covered by plastic film.

Wheel Set Resistor 4

Below is a comparison of the strip with an N Scale 3 axle tender truck.

Wheel Set Resistor 5

Once the chip resistor is popped out of the strip you can see just how small it is.

Wheel Set Resistor 6

And immediately you can see the advantage over the traditional resistor.

Wheel Set Resistor 7

The next issue is how to fix the resistor to the wheel set.  If you attempt to solder it on I guarantee it will go wrong.  The heat from the iron will heat up the wheel set and melt the plastic spacer between the wheel and the axle.  This will cause the wheel to become out of line and wobbly.  It may even cause a direct short across the wheel set.  The other option is to glue the chip into place.  This also has a few problems because if you get glue between the metal contact of the chip and the wheel or axle, the chip will not be able to conduct electricity.  To overcome this I have used Wire Glue made by Anders Products.

Wheel Set Resistor 8 Wheel Set Resistor 9

This is glue that has been designed so once it sets it will conduct electricity.

Unlike superglue or CA the wire glue needs time to dry, normally overnight, and that means it needs to be left where it won’t be knocked or moved.  Sitting one of those tiny chips on an axle that rotates is not very practical so I pop out the wheel sets and gently hold one of the wheels so the set can’t roll over.  Make sure what you are using to clamp the wheel set is not too strong as you don’t what to damage the wheel.  I would also recommend checking the wheel centers are correct before gluing the chip in as you won’t be able to move it once the glue has set.

Wheel Set Resistor 10

Once you are ready, and have stirred the wire glue, use a tooth pick to put a tiny amount on the axle and the inner face of wheel making sure you don’t bridge the plastic spacer with the glue.  Then using a pair of tweezers position the chip so one end touches the axle and the other touches the inside of the wheel.Wheel Set Resistor 11Once it has dried a little I put a bit more glue over the top to ensure everything makes contact.

Wheel Set Resistor 12

If, like this particular wheel set, both wheels have a plastic spacer you will also need to bridge the other side.  I have done this simply by spreading some of the glue across the spacer from the wheel to the axle.

Once dry you can check the resistance across the wheel set with a multi-meter.

This glue generates a fair amount of resistance itself so it would not be good for main DCC wires etc but for this purpose it does the job nicely.  I also don’t think it’s as strong as most glues so to make sure the chip won’t come off you could also put some superglue or CA over the top once you know it works okay.

Then it is a simple matter of fitting the wheel set back into the truck and the coach is ready for use on any layout and will trigger track detection on layouts with circuit detection.

Fitting Micro-Trains Body Mount Couplers To Older N Scale Freight Cars

With the NMRA (BR) Convention coming up this weekend I decided that some of my running stock needed some attention before the show.  A lot of my older rolling stock still has the Rapido style couplers and some of the newer stuff has Atlas’ Accumate couplers.  My preference for couplers has always been to use Micro-Trains as I have found them to be the most reliable.  In this post I will share with you how I convert older rolling stock to MT couplers in a fairly cheap way.

The box car below is a typical 40 foot car with Rapido couplers fixed to the trucks.  By far the simplest way to convert this car would be to buy a set of MT trucks, which come with couplers pre-mounted, to replace the originals.  However this can become very expensive if you have lots of cars to convert.

Micro-Trains Body Mount Coupler Fitting 1

Another slightly cheaper alternative is to buy an MT conversion kit that will replace the coupler in the truck.  These can be a bit tricky to fit but work very well and you get to keep the original wheels.  The car I’m converting has metal wheels which are clean and in good order, making it a good runner.

For me the cheapest option is to use body mounted couplers.  Again this means you get to keep the existing wheels and trucks but the existing couplers are removed totally.  The new couplings are fixed to the underside of the car chassis.  This is actually more prototypical and transfers the weight of the train through the chassis, bypassing the trucks and bolster pins.

The MT body mount couplers are available in pairs or in bulk packs as shown below which is certainly the cheapest way to buy them.

Micro-Trains Body Mount Coupler Fitting 2

To make the change you will need a few basic modeling tools as shown below.  I use a small watchmaker’s screwdriver, flat file, craft knife, needle nose tweezers, flat end tweezers, MT gauge, pin vice with a drill (from the MT Tap & Drill Set – 00-90), side cutters & pliers.

Micro-Trains Body Mount Coupler Fitting 3

To start you should check that the car is in good running order.  You can see I have already changed the left hand coupler.

Micro-Trains Body Mount Coupler Fitting 4

The body should simply pull off the chassis and can be put to one side.

Micro-Trains Body Mount Coupler Fitting 5

While the body is off it’s a good chance to check that the weight inside the car is properly secured; it’s normal for this to be rusty as it’s simply a strip of unprotected steel.  If the weight is loose simply glue it back into place before continuing.

Micro-Trains Body Mount Coupler Fitting 6

Next remove the truck by pulling out the bolster pin.  You can do this either with the pliers or by simply pulling on the truck.  Make sure the bolster pin does not fly off.

Micro-Trains Body Mount Coupler Fitting 7

With the truck removed the front wheel set can be taken out by gently pulling the truck side frames apart.

Micro-Trains Body Mount Coupler Fitting 8

Then using the side cutters snip off the coupler leaving enough material surrounding the bolster pin hole.  You won’t be able to do this in one snip as the truck side frames will be in the way.  I find five snips normally does the trick.  Once finished the top of the truck needs to be flush otherwise it may hit the new coupler.  If the area where you sniped is a bit rough you can use the file to smooth it out.

Micro-Trains Body Mount Coupler Fitting 9

The truck can then be loosely re-fitted, there is no need to push the bolster pin in hard as it will be removed again shortly.

Micro-Trains Body Mount Coupler Fitting 10

The bulk pack of couplers contains lots of parts but to assemble one coupler you need the five laid out below.  They are the coupler hook and catch plate, coupler box and top plus a spacer, screw, spring and drop pin.

Micro-Trains Body Mount Coupler Fitting 11

Using the craft knife remove the coupler hook and catch plate as well as the coupler box and top from the sprues.  The spacer is the flat part on the right and may be required later so put it to one side.

Micro-Trains Body Mount Coupler Fitting 12

With the parts removed there’s one small thing I like to do before assembling the coupler and that’s to use the file to deburr the top of the drop pin.  This simply makes it fit easily without too much force which can break the coupling hook.  The end that fits into the coupler hook is the longer leg.

Micro-Trains Body Mount Coupler Fitting 13

I tend to hold the pin in the tweezers or pliers and run the file on four sides of the pin at 45°.

Micro-Trains Body Mount Coupler Fitting 14

With the pin still in the tweezers or pliers push the filed end into the small hole in the coupling hook.  The pin should be at an angle which is parallel to the side of the hook.  The pin only needs to go through the hook so the end is just poking out of the top.

Micro-Trains Body Mount Coupler Fitting 15

With the pin fitted slide the coupler catch plate over the pin.

Micro-Trains Body Mount Coupler Fitting 16

With the coupler box on its back place the assembled parts over the tube in the box.

Micro-Trains Body Mount Coupler Fitting 17

The next part is the most tricky.  There are several ways of doing this but for me I like to use a pair of needle nose tweezers and a watchmaker’s screwdriver.  The risk is that the spring will ping off and, given how small these are, you usually can never find it.  Luckily MT provide several spares in the kit.  I find it’s best to get the spring close to the coupler and almost in the same orientation.  Then carefully compress the spring with the tweezers and place it over the slot between the coupler box tube and parts.  Using the screwdriver push the spring down into place and release the tweezers.

Micro-Trains Body Mount Coupler Fitting 18

Once in, the spring will stay there, but the assembly is very delicate so don’t knock it or the spring may ping out.

Micro-Trains Body Mount Coupler Fitting 19

Using the tweezers place the box lid on to the box and press down with your finger.  It should clip into place.  The lid only fits on one way round and the underside has groves to fit onto the box.

Micro-Trains Body Mount Coupler Fitting 20

Once the lid is clipped on the coupling is fairly robust and can be moved about.  Check that the coupling moves in the box and bounces back to the same central position.

Now it is time to fit it to the car chassis.  The particular set I am using are medium length, for a 40 foot box car. A short length might have been better but they will work just as well.

Place the coupling on the underside of the chassis and pass the drill through the box tube.  Once the coupling is as far back as you want it, ensure the truck can rotate and the coupling is centered, and use the drill to mark the chassis.

Micro-Trains Body Mount Coupler Fitting 21

Then remove the coupling and truck so you can easily drill through the chassis.  Depending on the make of the car the distance from the edge will vary, but I tend to find the hole needs to be halfway between the third and forth plank counting from the edge.  As this car has a plastic chassis the metal screw will cut its own thread.  However if the chassis is metal you may want to use the tap that came with the MT tap and drill set to cut a thread in the chassis.

Micro-Trains Body Mount Coupler Fitting 22

Next push the screw into the coupler box hole from the underside.

Micro-Trains Body Mount Coupler Fitting 23

I find pushing the screw all the way though and holding it with the needle nose tweezers helps keep the screw straight when you start to tighten it up.

Micro-Trains Body Mount Coupler Fitting 24

Once the screw is started you can let go with the tweezers and tighten it up.  Make sure the coupler is square before you fully tighten it. You will notice that the screw is now sticking through the floor of the chassis.  This is not a problem as it will be inside the box car but if your car has a veranda, such as you get on a caboose, or is simply a flat car, you will want to shorten the screw with the side cutters first. Note: you will also need to use a big set of side cutters for this as you may break a modeling pair.

Micro-Trains Body Mount Coupler Fitting 25

The truck can now be installed.  If the truck can rotate freely push the bolster pin in all the way and refit the wheel set.

Micro-Trains Body Mount Coupler Fitting 26

The last thing to do is check the height of the coupler.  Using an MT gauge as shown below this is very easy to do.

Micro-Trains Body Mount Coupler Fitting 27

Simply clip the gauge to the track, shutting off the power first, and test the new coupling with it.  Should the coupling be too high simply unscrew the coupling and add the spacer that we put to one side earlier. This will lower the coupling.  In the unlikely event that the coupling is too low then remove the trucks and add a washer to each; this will raise the whole box car correcting the coupling height.

Micro-Trains Body Mount Coupler Fitting 28

The box car is now ready for service.

As I said at the beginning the NMRA (BR) Convention is this weekend at Derby, England and I will be there along with my fellow modelers running the N Scale modular layout ‘Solent Summit’, and my new modules will be there.  The convention is open to the public on Sunday and it would be great to meet anyone who is coming along. If you can’t make it I will be giving a full report here in the coming weeks.  This week I will leave you with a taster from my new modules, below is a video of a ‘short’ train crossing the Warsash River on the Warsash Wye trestle.