Monthly Archives: October 2021

New Axles for a Second Generation Bachmann HO 4-8-4 Northern

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Back in 2018 I shared with you my design for replacement axles and gears for a HO Bachmann 4-8-4 Northern.  You can find the post here. That turned out to be quite the adventure, as simply creating replacement parts didn’t work out so well!  Due to the thinness of the original components I had to engineer a much thicker gear which could handle the force applied from the motor.  This turned out to be a success.  But this gear and axle set only worked for the first generation of the Bachmann HO 4-8-4.   As it turns out, although Bachmann redesigned and improved the second generation, it too has problems with split axles and gears, and I’ve regularly been asked if I could produce a set for this locomotive.  Well, I finally have and in this post I’ll share the design with you.

To start, I want to explain the difference between the three generations that are commonly available.  I’m not going to go into any of the body or cosmetic differences, just the drive train so you can tell which generation you have.

The first generation, as I’ve already covered in other posts, has a pancake motor which drives the rear axle.  Below is an exploded schematic drawing, courtesy of John on the Tyco Depot Train Collectors & Model Railroading Forum. You can just about see the gear on the rear axle.

Looking at the underside of the locomotive there’s a bump over the rear axle to make way for the gear. 

This is the main clue that it’s a first generation.  This locomotive also has round wheel stubs and holes in the axles.  That’s what makes quartering the valve gear tricky on this locomotive.  ‘Quartering’ means setting the piston rods and side rods on each side of the locomotive at 90° to each other; as the wheel stubs are round it’s easy to get it in the wrong place meaning the loco won’t run smoothly.

The second generation had a lot of improvements such as a can motor and thicker gears and axles.  But most importantly the axles and wheel stubs also have square stubs and holes, making quartering far easier to do. You can just about make out the cracks in the axle and gear.

Below is an exploded schematic drawing, also courtesy of John.

The motor this time drives the third axle and there’s no bump in the base plate; this along with the lack of wires running to the tender tells you it’s a second generation.

The third generation, which I believe is the version currently available, had a total redesign.  It still has a can motor which drives the third axle, but everything else has changed.  Looking at the exploded schematic drawing below, again courtesy of John, you can see the axles are a different shape. 

To my knowledge, these don’t fail.  These are normally marked as DCC ready and will have wires connecting the tender to the locomotive; the DCC socket and speakers for sound are located in the tender.

Looking inside the second generation you can see the axles and drive gear on the third axle. The second axle is clearly split and once I removed the others I discovered they had split too. As the wheel stubs are square they don’t need to be such a tight fit as the round ones on the first generation.

Interestingly the axles are almost identical to the axles used on the UK Bachmann (former Mainline) designed locomotives that I have 3D printed replacements, for as shown below.  These were for a GWR Hall class and can be found here.

However, upon measuring the US 4-8-4 axles and gears I found them slightly different, so a new design was needed. These have been designed to be 3D printed in Shapeways Smooth Fine Detail Plastic.

The kit I’ll supply will contain three axles and a main drive gear. The idler gear between the worm and axle gear to my knowledge never breaks so I haven’t supplied that; if yours has, please let me know and I will add it to the kit.

These have now been sent off for a test print and I’ll see how well they work.  As with the first generation, and the UK Bachmann locos, I’m restricted by the size of the axle box and the size of the wheel stub.  This means the axle itself nearest the wheel is still not as thick as I would like it to be, and it’s possible to crack the new axles if not cleaned properly before use.  Once I’ve test fitted a few, if it appears too easy to crack the new ones I will include a few spares in each kit.

So now I’m waiting for the 3D printed parts to arrive, and I’ll share them with you when they do.

Updating Your Digitrax Products

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As with most equipment, manufacturers often make improvements to their products after you’ve purchased them.  The nice thing with electrical equipment is these improvements are often related to the way it works rather than a physical change, so this can be updated.  In this post I’ll show you how you can check to see if your Digitrax equipment is up-to-date and if not, how to change it.

Digitrax equipment is very reliable and robust, but most of their equipment has had a small improvement made at some point.  Just like a computer or mobile phone, electrical equipment has a program that runs on the circuit boards. This program is called firmware, unlike software that runs on a computer, firmware is the program that tells the components what to do.

Below is an example of some common Digitrax equipment.  From left to right we have a DT602D radio throttle, a DT500 throttle, a DCS 240 command station, a DCS 51 command station and a PR3 USB to PC interface.  All of this equipment has firmware and all of it has an update available.

Some of the equipment, such as the newer DT602, tells you what version the firmware is when it starts up. Below you can see this throttle has SW Version 0000.1 and is dated July 15, 2021.

Other equipment such as the command stations and older equipment don’t have a such a clear display. But there are ways to find out what the firmware version is.  To do this Digitrax have a piece of software called DigiIPL and this can be downloaded from their website www.digitrax.com.  This software can be installed on a PC, laptop or Windows-based tablet, but don’t start it up yet.

To connect the Digitrax equipment to the DigiIPL program you will need a USB cable, which should have been supplied with the command station.  If not, the same type of cable often used with printers will work. The cable needs a USB Type A fitting on one end and a USB Type B fitting on the other as shown below

The newer command stations, such as the DCS 240 have a USB port on the front of the unit but the older models such as the DCS 51 do not. I’ll show you how to connect those later.

With the USB cable plugged into your computer and the DCS (DCS stands for Digital Command Station) connected to its own power supply, the PC will assign a COM port to it. This is the address of the connection, depending on what else you have plugged in this will be different for each user, we will find out what it is in a minute.

With the DCS connected you can now start the DigiIPL program and it will look like this.

You’ll notice at the top left a Loconet Port has not been selected, this is where the COM port is entered. Luckily you can only select from Com ports that are active, mine had been assigned to Com 4. If there’s more than one, try the first and if that doesn’t work try the next. It’s also important to note the ‘Bit Rate’ should be set to 16457 although by default it always is.

At this stage I should point out that if you have lots of Digitrax equipment, particularly lots of the same item, it is a good idea not to have it all plugged in to the command station at the same time when doing this. Theoretically it should work but it’s recommended to do this individually.

Once you’re ready you can push the ‘Find Devices’ button and it will open another window listing the equipment, and below you can see the DCS 240 listed and is at SW version 0.3.

If I plug in the DT602D from earlier and push the ‘Find Devices’ button again you can see it listed showing the SW Version 0.1 as we saw before.

So now we know the current SW (Firmware) version but how do we know if it’s the latest? Heading back to the Digitrax website on their downloads page they have all the available updates listed. Below you can see the DCS 240 is at version 0.4 and the DT602 is at version 0.1 so only the DCS 240 needs to be updated. (I did the DT602 the other week).

To update the DCS 240, or any Digitrax equipment, download the relevant firmware to your computer. Then using the ‘Select File’ button, select the downloaded firmware file.

Pressing the ‘Start’ button will now update the equipment.

Once done you can check to see if the update was successful by pressing the ‘Find Devices’ button again to check the version.

When it comes to the older equipment, such as the DCS 51 that don’t have a USB port, an interface is needed. This is where the PR3 shown in the first photo comes in. Below you can see the USB cable connected to the PR3 and the PR3 connected to the DCS 51 via a Loconet cable.

With the new equipment connected the DigiIPL has to be restarted. This time it has connected on Com 5. Using the ‘Find Devices’ I can see the PR3 and DCS 51, but only the DCS 51 needs an update.

And thats it, all up to date. It’s always a good idea to update any firmware, Digitrax or otherwise. The chances are you will not see a difference in how your device works but there’s a good chance it will fix a problem you didn’t even know was there.