Monthly Archives: January 2020

An N Gauge Dapol Britannia Driveshaft

Posted on by

This week I have a new product to share with you.  The N Gauge Dapol 4-6-2 Britannia is a great model.  But in a similar way to the N Scale Roundhouse, now Athearn’s, 2-6-0 and 2-8-0 steam engines, and the Atlas N Scale 4-4-0, this particular model also needed a new driveshaft and yoke.

The motor, and DCC decoder, is packed into the tender and a drive shaft runs through the cab to power the main driving wheels.  The motor axle has a yoke fitted to the end, as does the spindle in the cab.  A driveshaft connects the two yokes and allows the tender and locomotive to twist without breaking the transmission of power, just like a drive shaft does on a car without being affected by the car’s suspension or steering.

I modeled the three parts after taking measurements from the originals.  I made the driveshaft slightly longer as I’ve often had originals come apart when handling the locomotive. The set on the left are loose, but in order to avoid an individual part print charge, I’ve combined them into the set on the right.  None of the parts actually touch the sprew which can simply be cut away.

The parts were printed in Shapeways Smooth Fine Detail Plastic, as it’s the most accurate for small parts, and they came out very well.

On the model, it was the yoke on the motor axle which was missing.  This is normally due to the original splitting.  If the valve gear on the locomotive jams and the motor carries on trying to spin, the force can cause this to happen.

The new yoke, with a little bit of pressure, fitted onto the axle.  I’ve designed the hole in the yoke to be very slightly smaller than the axle so the pressure fit will prevent it from spinning on the axle.  Whenever fitting anything like this it’s important to make sure the inside of the yoke is clean and free from any 3D print residue, as this may cause an even tighter fit and could lead to the new yoke cracking as well.

As the old yoke on the locomotive spindle was intact I didn’t change it, but as you can see the new driveshaft fits well.

With the locomotive reassembled I also tried it with the original driveshaft; you can just make out the black spokes in the new tender yoke.

But I did find, as with the original setup, the driveshaft came out too easily.  The new 3D printed one is almost 0.8mm longer than the original and this helped keep it in place as you can see below.  Another alternative would be to slide the tender yoke slightly closer to the locomotive.

The last step was to test the new driveshaft and as you can see below I’ve lifted the locomotive driving wheels off the track for the first test.  I wanted to run the loco at speed for a while, and as the rear set of drivers have traction tires which are susceptible to coming off, I didn’t want to give them the chance.

The next test was to do several successful trips around the layout with twelve coaches behind, which it did with ease.

The Dapol N Britannia Driveshaft Repair Kit is available here.

This coming weekend is the NMRA(BR) Benson winter meet and I’ll be there with my fellow club members and parts of our ‘Solent Summit’ layout.  As this is only a one-day event we won’t be putting on a 5 Mile show like we did at Warley!

The event is at the Benson Village Hall, Sunnyside, Benson, Oxfordshire OX10 6LZ from 10am till 4pm. I hope to see you there if you can make it, if not I hope to get some photos to share with you next week.

Adding Power Pickups by DCC Concepts

Posted on by

As well as the drawing I do for 3D printing I do a lot of train repairs and DCC installs, particularly sound installs.  These can sometimes be a bit tricky and I often have to use other products to make it work.  Normally I don’t do reviews of products but recently I found something that worked so well I wanted to share it with you.  In this post, I’ll show you what I did to add additional power pickups to a Hornby OO B17 with plastic wheels in the tender.

The B17 has been around for many years and every now and again it gets a facelift as parts are re-tooled and improved.  The most recent version is quite fantastic, but the previous one had, in my opinion, one major problem.  The tender was the same design from many years before, and still had plastic wheels.  The two pictured below are of this version; you can tell by the basic molded coal load in the tender.

This means although the locomotive had been re-tooled to include power pickups on all the drives, it still only had the pickup footprint of an 0-6-0.   For DC operation this is often just fine, but DCC, and in particular DCC sound, the decoder required an unbroken power supply and when you factor in dirty track, dirty wheels, and dirty pickups, the 0-6-0 footprint on this loco simply wasn’t working.

Looking under the tender you can see the plastic wheels and even the hole above the third one which allowed a strip of card with a rough surface to hang down.  A cam on the last wheel used to rub against the surface and make a kind of chuff effect; this dated back to the 80’s and Hornby called it their ‘Realistic Chuff’ effect.

The red you can see through the hole is a stay alive unit.  This locomotive is fitted with a Zimo Sound decoder, but even with the stay alive, if the loco stopped in the wrong place it wouldn’t start again without a push.

The axle for the wheels is simply a bar and the plastic wheels are in two parts.  This design has been repeated on many locomotives of early design.

The first problem is to find metal wheels to use.  The reason why it’s a problem is just about all the current metal wheels come with much shorter axles with pointed ends.  But the old Mainline or Replica Railways (which is now Bachmann) locomotives had metal wheels in their tenders which were the exact same size on long axles.  Of course, this does mean sacrificing another loco but six axles from two tenders is enough to do three Hornby locos as I’ve only replaced two wheelsets in each tender.  An afterthought would be to see if the plastic wheels fit in the Mainline or Replica Railways tenders?

I found two types of wheelsets in the Mainline/Replica Railways tenders.  Some, as with the set on the left, have metal wheels but a plastic axle which doesn’t end in a point.  The center and right side wheelset both have metal wheels and a metal axle, electrically isolated, with pointed ends.

As the original Hornby axle measured  26.35mm I wanted to get as close as I could.  Any longer will cause binding and make it harder to fit the new wheels.

The set with the plastic axle came in just under and worked perfectly without modification.

The set with the metal axle was ever-so-slightly longer, but this was easily remedied by filing off the points on each end of the axles.

As you can see below both types of wheelsets fitted into the tender and they all rotated  very well.

The second issue was how to collect the power from the metal wheels.  Over the years I’ve built many homemade pickup systems, normally from strips of brass that rub on the wheels at some point, but it doesn’t always work well and the pressure of a flat strip rubbing on the wheel creates a lot of drag.

Then I discovered DCC concepts’ gold plated bronze wheel wiper sets.

The pack contains 12 sets of wheel pickups, each picking up from both wheels and a pack of screws for mounting.

The actual pickup is a strip of PC board with two folded brass contacts, both gold plated.  The contacts have a rounded section to provide a pinpoint contact on the wheel which will reduce drag.  Next to the mounting hole are two solder pads, one for each side.

The rear simply has the connection between the pickups and the solder pads.

As you can see below the pickups fit perfectly between the wheels and provide just the right amount of pressure to ensure a great contact with the wheel.

Now it’s time to fit them.  With the tender shell removed you can see the metal weight.  It will be important to keep this as it’ll ensure the wheels keep good contact with the rails, but it’ll need to come off for now.

The weight was held in place with a few spots of glue.

With the new wheels fitted the pickups can be moved around until the ideal location is found.  You need to make sure the rounded part of the pickup is in contact with the middle of the metal wheel flange and not the plastic inner.

Then using a pin vice I drilled a hole, smaller than the screw, in the tender chassis using the hole in the pickup as a guide.  The screw will cut into the soft plastic of the chassis.

The pickups can now be fitted in place.  I also fitted the wheels again at this point to test everthing worked properly.

The screws were longer than the thickness of the plastic chassis and protruded out of the top. That’s why I removed the weight, and they need to be cut and filed down to refit it.

I refitted the weight using some Black Tack, it’s very sticky and malleable, which is ideal for this job.

The solder pad can now be linked with wire.  If you have a large soldering iron you may want to solder the wires on before the pickups are fitted to prevent caching the chassis with the iron as it will melt very quickly.

Lastly, I solder on two wires to connect back to the main locomotive pickup points.  It’s important to ensure you match the tender wheels from the correct side with the loco wheels or it will simply short out.

With the tender reassembled and all the wires connected it was time to test the loco, and it ran very well.  The best test was to raise the loco off the rails, so it isn’t picking up any power and see if the tender pickups worked on their own, which they did, as you can see in the short video below.

I could’ve fitted three sets to the tender, but after testing two proved to be plenty, and both the B17 locomotives from the first picture are now running equally as well as the latest version of this locomotive, which comes with factory fitted tender pickups.

These pickups from DCC Concepts are very good and, I think, very well priced because you get 12 in a pack.  I’ll certainly be using them again. I just hope they bring this product out for N Scale.  You can get the pickups direct from DCC concepts or at a stockist such as Model Railway Solutions in Poole.

Next week I’ll share with you some of the 3D printed parts which arrived last week.

A Quick Post of New Parts

Posted on by

This week’s post will be short as I just want to give you a look at what arrived in the mail today from Shapeways.

The large spikes at the top are exactly that; spikes to repair a track system for a wooden toy train. The assembly below contains lots of gears, axels, a drive shaft and a set of drive shaft couplings.  These are to repair several locomotives such as the N scale Doodlebug from last week’s post, an N scale Minitrix diesel, an N Gauge Dapol Britannia and a HO scale Samhongsa brass locomotive.

After the parts are tested I’ll share the outcomes with you, but for tonight it’s back to the workbench, as some unexpected jobs have come up.  Next week I’ll have a review of a new product I found that was a tremendous help in upgrading some older steam engines to DCC sound.

A New Gear for the New Year

Posted on by

Happy New Year!

This week I’m starting the New Year with some small 3D printed parts to repair a Bachmann N Scale Doodlebug.

The Doodlebug is the name given to a self-propelled railcar originally powered by a gasoline engine with a direct drive or connected to a generator to power traction motors.  They started to operate on small lines around 1907 as they were more economical to run than steam engines.  Typically they ran on their own but could pull another car if needed.  Below is a photo, from Wikipedia, of Santa Fe Doodlebug number M.119 at Isleta, New Mexico in 1943 with its extra car.

Backmann’s model is very similar to M.119 and is a mixed passenger and mail carrier.  It has a motor near the front which powers the front truck only.  The rear truck is free-running but also picks up current from the rails.

Both of the front axels have gears so they can be powered. The gear is molded into the plastic axel which electrically isolates the two wheels.  It’s impossible to see but the axel that’s been separated from the wheels has split.

This causes two problems; firstly, as the split is between two gear teeth causing a bigger gap, the meshing gear won’t line up correctly and this causes the doodlebug to click or lump as it runs down the track.  Eventually the gears will jam.  The second problem is the wheel will spin in the axel; this results in a loss of traction as the motor won’t drive the wheel.

The axels in the rear truck have also split as you can see below.  I’m unsure why these have split as they’re not under any load, but my theory is simply the pressure applied from the inserted wheel stub forced the axel apart.

The other gears in the truck tower all seem to be in good condition and I think this is because they don’t have anything like the wheel stubs pushed into them, forcing them apart.

To repair the Doodlebug I’ve drawn a replacement gear axel and plain axel which will be 3D printed in Shapeways Fine Detail Plastic material.  I use this material because it’s hard, smooth, and prints to a very high accuracy.  I’ve made the hole through the axels ever so slightly smaller than the axel so it will be a tight fit.  But hopefully not too tight so that it splits the new axel.

In order to keep the cost of the parts to a minimum, two gear axels and two plain axels have been joined on a loop of 3D printed material.  They don’t actually touch the loop so it can be cut off and used without any burs.  That’s a great advantage with 3D printing.

These gears have now been ordered for a test print and once they arrive I’ll fit them and show you how they perform.  If all works okay I’ll make the repair set available in my shop.

I know for a lot of us modelers there’s never enough time for the things we need or want to do, but I hope this year brings for you, as well as me, the opportunity to get some of those long thought out or dream projects done. Here’s to a productive 2020!