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Futuristic Locomotive I2X2

Let’s begin at the beginning of all projects – the inspiration. The I2X2 was born from the success of my first engine, the I2X1. Ever since I finished the aluminum I2X1, I wanted to make a steam version, a predecessor so to speak. The idea floated around my head for three months before I got serious about it. I decided that I wanted this engine to be mostly copper and brass, to make it seem older and less advanced than the I2X1. I still wanted it to be sleek, but I had no problem with it being longer and bulkier – miniaturization is a difficult concept for early designs. The larger size would also let me get more creative with the electronics I planned to stuff inside the engine. This guy was going to have sound (my first one didn’t) an auxiliary motor, and a full complement of LEDs. With the basic criteria set up, it was time to choose a frame. 

I asked around at the Penn State Model Railroad Club and sure enough, one of the members had an old Mantua 2-6-6-2 articulated frame he was willing to part with. Originally, I wanted something with big drivers, but this articulated was perfect for the project – the mechanism looked cool in motion, the small drivers left enough room for me to add some cool things to the boiler area, and the hinged chassis could handle tight radius curves without any problems. Upon receiving it, I checked to make sure it ran well – it wasn’t amazing, but a quick tear down and clean up / re-lubing did the trick. Replacing the flexible rubber tubing connecting the articulated sections together got rid of any vibrations. Once everything was in operating order, I stripped away all of the unnecessary parts and was left with just the drive mechanism and front and rear trucks. 

After acquiring the frame for the locomotive, I got sidetracked for other projects, and the parts lay around in a ziplock bag on my desk. One day I was digging through my “random bits bucket #4” and laid out some parts on the floor. An old East German ball bearing, assorted copper tubing cutoffs and an aluminum hub/spinner from an RC airplane. I found myself playing around with ways I could assemble the parts when it dawned upon me that this could make a really awesome front section of a streamlined boiler… hmmm.

The parts weren’t perfectly aligned, but that didn’t really worry me. I chucked up the entire assembly in my corded Dewalt drill and smoothed out the contours on a belt sander. I know, a lathe would really have come in handy, but I didn’t have one, and the spur of the moment inspiration mandated that I act immediately with whatever tools I had at my disposal. After finishing the rough shaping for the front of the engine, I moved onto the frame. Here I took a lesson from the first locomotive and decided not to mill the entire thing out of one solid chunk of metal. This would have taken too much time, limited my design options, and reduced the usable space inside the engine. Still, preferring to work from a solid foundation, I cut a simple rectangular frame out of a 1/4″ thick piece of copper bus bar donated by a club advisor. Chunky overkill? Yes. At least the loco would have good traction…

Doesn’t look like much, but this is the imagination kicks in. In order to keep everything running nicely and without shorts, I had to get clever in mounting the running mechanism to the frame. I used a series of standoffs and screws, along with a styrene shelf to keep pressure on the front section of the drive mechanism. This allowed the front part to swing freely in tight curves while keeping the body of the engine aligned with the back drive mechanism. 

Fabricating a Tender

I scrapped the original tender that came with the engine because I thought it was far too small. I made one twice as long out of the same 1/4″ thick copper bus bar. The undercarriage was made out of 1/8″ thick black styrene to keep things electrically isolated. I tried running the engine without tender pickups and that went very poorly on dirty sections of track and unpowered frogs, so I needed to make pickups for the trucks in the tender. These were made from thin phosphor bronze strips.

I made the tender out of 1/32″ thick copper sheeting, leftover from an expensive gutter job one of our club members did. I was very lucky to get the scraps for free, and ended up making most of the engine from the material. Initially, the tender was just a copper box on wheels. I soldered the sides to the (rather massive) 1/4″ slab of a frame using a Map gas torch and a set of clamps. This was the first time I did such a large soldering job and it took a bit of trial and error to get the joint to my liking. I left the sides extra tall to give me plenty of area to work with when I figured out the final shape of the tender.

Designing a Complicated Headlamp

With the tender starting to resemble something… tenderish, I shifted my attention to the next task – attaching my beloved nose cone to the frame of the locomotive. Having just had success soldering large copper parts, I went ahead and tried to solder the copper parts of the boiler to the copper frame. As I was heating up the parts, the clamp slipped and the engine hit the floor. I quickly splashed water on the parts so as not to melt the coating on the floor tiles and frantically waved at the smoke and steam to keep it from reaching the smoke detector a few feet away. This was all done in the basement of a 10 story dorm building, so setting off the fire alarms was the last thing I wanted to do. It is impossible to put into words the rage and frustration I felt at that moment. This was the aftermath of my failure to secure the workpiece before applying heat. Class was in session at the school of hard knocks.

Still, the desire to see my imaginary engine run was greater than the dejection inflicted by the previous failure and I came back the next day and cleaned up the parts. I decided to hold off on the soldering for a bit and worked on the engine’s headlight. You might be thinking “oh, that should be easy, just solder up and LED and resistor, this kid’s got it”. That was my original idea. However, the moment I showed club members the nose cone with the embedded ball bearing, they challenged me to make it rotate, with the headlight poking through the center of the bearing. Below is a mock up of the feature:

I spent about a week exploring different ways to accomplish the effect I was after, and decided to use slip rings to power the spinning LED. The LED was permanently mounted in a brass tube, with its leads isolated from the tube using 5 minute epoxy.

I used multiple thicknesses of brass tubing to capture the small 1/4″ OD ball bearing on the shaft. The LED leads were pulled through the hollow center and out two small holes further down the shaft. The brass tubing extension fore of the 1/4″ bearing was pressed into the inner race of the larger “old” bearing, translating the motion of the rotating shaft to the inner race and balls of the front bearing.

A layer of Kapton tape was used to isolate the two brass slip rings from the shaft. The LED leads were *carefully* soldered to the outside of the rings in order to leave a smooth surface for the contacts of the slip ring assembly to ride on. This took a few tries to get right. The contacts were mounted to a styrene bracket that was screwed into tapped holes on the inside of the front boiler.

I tested the connection of the slip rings for a few hours, running the shaft using a small 6v gearmotor. Then I took everything apart and tried to solder the front boiler to the chassis. Second time’s the charm, right? This time I clamped everything down securely and even used some steel wire to keep things in place if the clamps slipped off the curved surface of the boiler. Thankfully everything held this time and the nose cone was attached to the frame by it’s copper components. You can see the nice solder filet in the picture below:

Let’s Call This a Steam Turbine, Okay?

With the front of the engine starting to shape up, I moved along to the exciting part of the model – the steam turbine. Now, this isn’t your standard steam turbine. This is what I envision powering an imaginary steampunk super locomotive. The inspiration for the design came from a revolver, and I imagined each steam chamber firing off a round of superheated steam and then rotating to be refilled with water while the next one kept the pressure up. I assembled the six shot cylinder from brass tubing, carefully cut and chamfered to fit evenly into holes drilled in two brass end plates. Soldering this piece took a few attempts with a small butane torch. When things cooled down a bit, I took the cylinder over to the belt sander and smoothed out any irregularities. I also opened up some elliptical windows in each of the six tubes. At that point, I just thought it looked cool.

After playing around with a few scrap pieces of clear acrylic, brass tubing and leds, I found the effect I was looking for and decided to implement it in my steam turbine. I pressed clear acrylic rods into the cylinder tubes and glued SMD LEDs to the back end. The LEDs I used were one of the tricks I had up my sleeve going into the project. These LEDs had 3 diodes in the same chip (RGB) and also had an integrated PWM driver, all in one convenient package! They were individually addressable using TWI and could be daisy chained. Their PWM drivers were capable of providing much nicer colors and transitions than a stock RGB LED driven by an Arduino, and placed very little load on the microcontroller. I could extol their virtues for a few more paragraphs, but that might bore some of you. Adafruit sells them for $4 per ten LEDs, they are called DotStars. Check them out.

Adding the First Body Panels

Looking back, I probably could have done a neater job with the wiring on the cylinder, but I think it looks kinda cool. The inner ring is the +12v rail, the outer ring is ground, and the other pins on the LEDs are the clock and data lines that control the lights. At this point I took a break from electronics, wiring and stressful slip ring construction and worked on the body of the locomotive a little bit. The club had recently acquired a milling machine, so I took the liberty to mill a streamlined cow catcher. I started by soldering two chunks of copper bus bar together and then milling them square. Then I milled out the slots for the mounting screws and the front truck clearance. Lastly I shaped the aerodynamic front by hand on a belt sander.

The rear edge of the nose cone wasn’t looking as good as I had envisioned so I decided to make a cowl to hide it. First, I cut out a paper template and drew the approximate shape of the shroud I wanted. Then I cut it out and tweaked its profile before gluing the template to a sheet of copper with white glue. This was rough cut with a band saw and nibbler and then honed on the belt sander. The piece was then bent around a wooden form and carefully soldered to the frame. Thankfully there were no mishaps this time. A bit of metal polish gave a sneak peak at what the finished engine would look like. Now that’s starting to look more like what I had in mind.

Custom Sliprings and Spinning Things

Now back to more slip rings and fun things. I needed to make a 4 contact slip ring in order to power the LEDs in the steam turbine. I used the same method as before, insulating the rings from the center shaft with Kapton tape and then soldering thin feeder wires between the rings and LEDs. Also note the insert on the inside of the main shaft in the picture below – I made it to index with the flat spots on the output shaft of the gearmotor I planned on using.

After all the wiring on the slip rings was complete, I covered the back end of the steam turbine with 5 minute epoxy. This would keep everything isolated from shorts, and help protect the thin magnet wires connecting the slip rings and the LEDs. I did not want to have to go back in there and fix anything so I made it permanent. The next step was to mount the auxiliary gearmotor that drives the entire assembly to the frame. I machined a simple motor mount out of 1/4″ copper plate.

Originally I wanted to use tiny bolts to secure the mount to the frame, but I ended up breaking a tap in the second hole. This was rather frustrating, and I was tired, so I just decided to permanently solder the mount in place. That worked fine, until I realized I could no-longer remove the running mechanism from the frame… and as that would seriously compromise the serviceability of the model, I had to unsolder mount and make two mounting holes 1/8″ back from the messed up ones. I added two extension feet to the mount in order to match the new hole pattern.

Everything fit perfectly this time around, and I was still able to disassemble the model completely. I had fun test running the motor to see that everything worked as planned. Thanks to the two ball bearings in the nose cone, the assembly spun freely and hardly taxed the motor at all.

The next step was to make the mount for the four wipers for the slip rings. This was also machined from the copper bus bar and mounted to the top of the motor mount with two bolts.

The wipers were made from phosphor bronze coupler box springs, and soldered to sections of square brass tubing. These sections slid onto a square plastic bar, which was glued to a grey styrene spacer. This spacer provided the right amount of tension in the wipers, and was epoxied to the copper wiper mount. Wires were soldered to the sections of brass square tubing to power the steam turbine for testing. This testing phase took a while, as I was having way too much fun playing with all of the color and animation combinations. I ended up settling on a red glow with a rotating yellow/white flash to signify the firing of each tube.

Adding More Lights

While on the subject of LEDs, I figured I could add another lighting feature to the rear of the locomotive. I had at my disposal various diameters of clear acrylic rods, so it was only a matter of time before I cobbled together some outlandish “heat exchanger machine”. This technology was so advanced, even I didn’t know how it worked, but that didn’t bother me – it looked the part and fit the theme of the engine. 

These V-shaped light pipes were to be mounted directly to a row of 5 DotStar LEDs. I prepared a simple circuit board to hold the LEDs, and make all of the proper connections. I ran two bus wires along the board, one for +12v and the other for ground. Soldering the LEDs proved to be a bit tricky, as even one poor connection rendered the entire string inoperable (since all of the data/clock lines were daisy chained together).

The last step to finish the heat exchanger unit was to wire in a plug and add a styrene backing plate to the underside of the circuit board. This would isolate the unit from the conductive frame of the locomotive and provide a solid mounting point. My first locomotive had numerous issues with electronics shorting out across the frame, so I tried to avoid making the same mistakes the second time around. 

At this point, I decided to take a break and take a family photo. The I2X1 parked next to the incomplete I2X2, with a mean vandal deterrent in tow:

Revisiting the Tender

With all of the exciting progress on the electronics and special effects for the engine, I had neglected to do anything with the tender. At this point the electronics were starting to pile up and I was beginning to have doubts that I would have enough space to fit everything into the tender. If you remember, at this stage it was just a tall copper box on wheels. Before fitting the electronics, I decided to make a removable styrene platform, allowing me to extract everything and work outside the confines of the copper tender. I also made a styrene enclosure for my speaker, which would be mounted to the front of the electronics platform. I experimented with the speaker orientation and found that mounting it upside down on an 1/8″ spacer provided the best response.

With the speaker mounted and the sled complete, I installed the electronics… despite the messy appearance, it’s actually quite neat and orderly in there. You can make out a Soundrax TSU 1000 Medium Steam sound decoder on the bottom of the stack. On top of it is my power regulator, coupled with a bridge rectifier and some filtering capacitors. On top are the brains of the beast – an Arduino Pro Mini (later to be swapped out for an Arduino Nano). I attached a heatshrinked optoisolator chip to the other side of the stack, to act as an interface between the Arduino and the Soundtraxx auxiliary function outputs. There is also an H-bridge driver for the auxiliary gearmotor, not pictured.

The aesthetics of the tender took a lot of trial and error to get right. I tried at least five different paper mock ups before finding something that delivered the look I wanted. Then I transferred and cut the pattern out of copper sheets. These shapes were then bent and rolled by had to get a nice sweeping profile. I used a cheap round pencil to help me get the curves consistent.

Then I clamped the short end panel perpendicular to the long bent panel and silver soldered it. This was my first experience with silver soldering. Things didn’t go smoothly at first, as I didn’t have enough heat and flux, but eventually I got the hang of it. The reason I opted for silver solder on this part was that it needed to be soldered onto the side of the tender without falling apart in the process. This way I could heat it up without having to worry about the end piece becoming unsoldered from the longer contoured panel. Here is one of the sides, prior to clean up:

Prior to attaching the panels to the tender, I cut the tall sides to to a nice curving shape on the bandsaw. I honed the shape on a belt sander to have a gradual downward slope towards the rear of the tender. Thanks to the silver soldering in the previous step, soldering the side panels to the tender turned out to be quite easy. Being mostly flat, they were easy to clamp and heated up quickly making nice soldering joints. Some work with a scotchbrite pad took away the ugly discoloration and restored the tender’s shine.

The tender was missing a rear light, so that was the next task. I drew inspiration for it from the multi-ringed lights I made for the I2X1. I started by drilling a 1/4″ hole in the rear of the tender and soldering a brass tube into it. 

I cut this tube down to size and then soldered on a larger diameter brass tube concentrically with it. I glued a smaller diameter aluminum tube into the center tube to add a bit of contrasting color. Then I pressed a clear acrylic rod into the aluminum tube to act as a light pipe leading to the inside of the tender.

I added a styrene fin to the back end of the electronics sled to hold the rear LED. I really wanted to have the sled be removable and easy to service, so the LED couldn’t be attached directly to the light pipe at the back of the tender. Since the project already had 11 DotStar LEDs, I daisy chained this one onto the rest. This way I only had to use two Arduino pins to control 12 individual LEDs.

Filling in the Gaps

The tender was starting to look respectable, so it was time to switch my attention back to the rear of the engine. I needed to add some structure and body panels to hide the gearmotor and obscure the heat exchanger (it looked way too much like the glowing hot exhaust headers of a V10 racing engine in its exposed state). I began by soldering two copper wire arcs to the locomotive frame. The clamps were there as a heat sink to keep the front of the locomotive cool and minimize the chance of something melting or coming unsoldered. I wasn’t going to take any unnecessary risks at this point.

Bringing in another element from the I2X1, I made two of these copper windings to place between the arcs:

I kept adding more structural elements to the area, trying to keep with the overall visual flow started at the front of the locomotive. The top rectangular brass tube served as a nice backbone from which to suspend the copper and brass webbing. Then I decided that I didn’t like the look, and preceded to cover up most of the section with copper sheet, curved to fit the contour of the arcs.

Finding the gap between the newly added roof and the frame to be an eyesore, I made two brass panels to cover the area. I drilled holes in a diagonal pattern, although the photo seems to suggest I missed a few centering punches when I was doing so. As they say, “good from afar, but far from good”.

Things were shaping up nicely, but there was still the dilemma of what to do with the middle of the engine. It was tempting to leave the auxiliary motor and its associated mechanism out in the open and accent it with some structural and detail parts. However, I felt that the engine lacked continuity, the flowing front and rear areas disrupted by the mechanical middle section. After some trial and error involving more paper templates, I decided to cover up a large portion with a curved copper sheet. Using the same method described earlier, I cut, sanded and bent the following body panel:

Soldering the panel to the frame as I had done with the previous two was out of the question, as I needed to access the mechanism underneath to take the engine apart for servicing. I consulted several club members and settled on small countersunk flat head brass screws as my fastener of choice. I took a lot of care tapping the holes for these – I probably would have thrown something at a wall if it had snapped in the frame. 

I soldered some small accent strips to dress up the lower rear portion of the large body panel. These matched the wrap around side panels on the tender and helped tie the two together.

With most of the soldering, drilling and tapping work on the frame finished, I installed the electronics into the body of the locomotive and added plugs to the ends of the wiring harnesses. Each plug was marked with a blue paint pen in order to indicate polarity. The plugs allowed me to make everything removable for ease of service and troubleshooting. Testing revealed that everything still worked. 

I was still a bit unhappy with the open space where the steam turbine was located, so I decided to make a removable cover to add some interesting lines and hide some of the internal mechanism. This was made out of copper and brass, its curves making soldering it together an exercise in creative clamping techniques. This simple piece helped bridge the gap between the large copper panels and the mechanical inner workings of the engine.

Finishing Touches

Aside from the programming, the last major component awaiting completion was the tender lid. I decided to keep things simple and opted for a friction fit with the tender walls, similar to an altoids tin. First, I traced the outline of the tender onto a piece of paper, then transferred it to a piece of copper sheet. This was cut out and bent to fit the curved top of the tender. Then I wrapped the perimeter with a long rectangular strip of copper and soldered it in place. This piece would keep the lid secure. Once again, I used a belt sander to match the profile of the curved top, giving me a nice, thin lip. 

Finally, it was time to let the I2X2 loose on the layout. This engine is truly exciting to run, and although I haven’t taken it to any shows, I’m sure people would enjoy it as much as the I2X1, if not more. It has spinning lights, sound and is shiny enough to see your reflection in its sides. Traction isn’t an issue as it is quite heavy, and it handles curves and sections of dirty track really well due to its multiple pick ups. Will I be making any more engines in this style in the future? I don’t know. I’d have to really get inspired by something to put the creative gears in motion. For now I think I’ll delve into the more conventional side of model railroading. Who knows, maybe I’ll get bored and make some outlandish cars for my locomotives to haul.

I’d like to thank Mike Greene and John Balogh for their help with this project. I owe you guys a lot. The same goes to the members of the PSMRRC. I have one last thank you to you, the reader, for making it all the way through this build log. I hope you enjoyed it.

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