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Futuristic Locomotive I2X1

It all started with a joke, something silly. Perhaps it was the Top Gear episode where they turned cars into trains, or someone at the PSMRRC club putting a ridiculous shell on a locomotive chassis, but somehow I got the bug to build an obnoxious, over the top locomotive. The thing is, I had been a part of the club for 3 years and never really cared for running trains – the engines were all standard, and I wanted to run something special. Sure, some members had nice brass steamers, but I knew I had no chance at getting one for myself. What do I do when something is too expensive for me to have, but I want it? I build it myself, or at least I attempt to.

In its infancy, the idea was open ended – I wanted something shiny, with the ability to house a lot of LEDs (I enjoy working with tiny SMD LEDs, some people think I’m crazy). As an engineering student, I defined some parameters. The engine had to run reliably and be able to pull some passenger cars or a medium sized freight train at main line speed. The engine had to conform to NMRA standards in order to run on the club layout, and also needed to fall under the $150 budget I allocated the project. Eating ramen noodles and Mac N Cheese every night was so worth it. 

Stumbling to a Design

That week I asked club members about reliable chassis and started up my ebay search filters. After a bit of deliberation I grabbed a used Proto 2000 SD 9 engine for $35. Next, I installed a $15 Digitrax N scale decoder and ran the engine around the layout a few times. I ended up tearing the entire thing apart and cleaning and re-lubing the gearboxes and trucks. This was the first time I had taken apart and serviced a model locomotive, and I had a lot of help from other club members. That same week, I saw a 2.5″x1.5″x10″ chunk of 6061 aluminum on ebay going for an absurdly low price and had to get it. It was at that moment that I decided to build the entire thing from a solid block.

First, I cut drilled holes and cut out the rough shape on a bandsaw. The club has a small desktop Ryobi bandsaw that managed to cut anything I threw at it. Then I handed the block off to one of our club alumni members, who had access to a milling machine. I probably could have milled it myself in one of the university machine shops, but they are perpetually crowded with students desperate to finish their project on time, so the machines aren’t in particularly good shape. 

As you can see, the shell took a number of machining operations. At the end, most of the vertical walls were 1/8″ thick, and the slopes in the front and back had about 1/4″ of material to allow me to do the final shaping using a belt sander. The inside was finished with a 3/8″ ball mill to maximize the area available for electronics.

Adding Electronics

At this point I thought I had plenty of space for everything, but things got cramped REALLY quickly. Let me elaborate with a diagram:

It looks half decent on a computer screen, but gets pretty busy when you have to fit everything inside the conductive aluminum shell of an HO scale locomotive. I had to paint the inside of the shell with nail polish (which I borrowed from one of my female friends and never returned) to keep everything isolated. As you can see, I relegated the main motor control and loconet communication duties to the Digitrax decoder – it’s good at doing that. The rest of the animations were controlled by the Adruino Nano microcontroller, passed from the decoder to the Nano via the headlight, rear light and F3 functions.

My system needed +5v and +12v dc so I dropped in my own power supply and bridge rectifier to provide a stable supply for my logic and LEDs. Remember when I said I wanted to use a lot of LEDs? By the end of the build, the loco had 51 leds in total. Most of those were driven by a specialized LED driver chip (TLC5952) I got from TI as a free sample. It came as an SMD package so I had to get creative and make breakout boards. I used a laser printer to make the mask, transferred the toner from the paper to my board using a hot iron, and then etched away the bare copper in a heated and aerated HCL and H2O2 solution. Not too bad for a college dorm…

One of these boards went into the locomotive, the other was saved for a future project. I also made up two boards that attached to both sides of the driver chip at 90 degree angles, which held 24 bright blue SMD LEDs each. The brightness of each LED could be controlled by shifting out a pwm value through the built in SPI interface. Additional resistors were added to complete the circuit (a few pull up/ pull down, and a single resistor to set the global current limit for the LEDs) and the assembly was dressed up with brass tubing to look like some sort of warp drive. The tubing also acted like a heat sink to help the driver dissipate some of the heat generated during long operating sessions.

The LEDs were sequenced with an IR cam to look like the pulses from the warp drive were driving the locomotive. In fact, in a stroke of luck I was able to time them so it looked like the pulses were standing still in relation to the surrounding scenery as the locomotive moved. The IR cam was a simple IR diode/transistor pair mounted on a breakout board I got from Sparkfun. I taped a 1/8″ wide strip of black electrical tape on the forward flywheel of the motor to act as the beam interrupter. The last electronic component was the auxiliary motor I used to drive my faux turbine.

The turbine body came from my spare parts bin – it originated as a Bostitch hand cranked pencil sharpener. The center axle was made out of various sizes of brass tubing. It is linked to a 12v gear motor mounted in the back of the locomotive body with an O-ring drive, making the system quiet and easy to service. The tension of the O-ring keeps the assembly in place and locked into the surrounding structure. As you can see, it’s pretty tight in there.

Finalizing the Body Shape

Now, back to the shaping of the body. After I got the shell back from Mike (the guy who agreed to machine it for me) it had a few dings and machining marks that needed to be removed, and all of the sharp corners had to be rounded off. However, I couldn’t resist running it around the layout a few times before beginning the tedious work.

It already looked like something! At this point I asked Mike to machine some more space for the electronics, as evidenced by the red marks on the roof cutout. After this was done and a hole was bored for the headlight and rear light, I introduced my chunky aluminum friend to the belt sander. First it was 60 grit, then 80, then 120. After that it was on to hand sanding  – 220, 320, 400, 600, 1200(wet), 1500(wet). This was the most time and energy consuming part of the project.

Quite the contrast from the previous picture to this one, right? It was at this point where I knew I was doing something right. Before then, it was all just done based on a feeling, a thought of what was right in my head. Now that there was something tangible appearing out of that thought, I was pleasantly reassured that my intuition was going to yield something unique, almost beautiful. I threw together some of the rear mechanism and grabbed some more photos.

Here you can see the painted details I highlighted in the trucks. The headlight took a few iterations to make, but I was incredibly happy with how it turned out. It consists of an outer brass tube, lined with acrylic backlit with a bright blue LED. The center section is kept separate from this “halo” with another brass tube, which holds a standard size white LED. Both lights can be dimmed and faded separately using the PWM output of the Arduino Nano. I posted this picture to our club’s FB page as a teaser:

The halo effect is clearly visible. The polish is starting to get to the absurd shiny-ness I demand. Unfortunately, there were still machining marks visible on the side where the bevel of the ball end mill went too deep. After trying to sand those marks away for a few hours, I gave up and covered the area with a gold pinstripe. Looking back, the pinstripe version looks way better than the plain shiny side.

Testing and Tweaking

Aside from a few tweaks to the electronics and code, the locomotive was complete. Time for some fun!

And last but not least, a video to see how the finished engine runs:

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