Susquehanna Boxcar 6S Pro Max V3 Platinum Edition: The Buildening and Dragon Con 2025 recap!

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So typically, a Boxcar update involves Motorama, my perennial winter robot festivity back north of the Mason Dixon line. However, in 2025, conflicting work travel turnaround times made it basically infeasible to commit to going. Therefore, while a lot of the design and some of the building of Boxcar happened over winter (and some really dating back before Dragon Con 2024), I really just targeted getting it together for last year’s Robot Battles.

We begin the story some time in late summer 2024 (Man, I’m keeping this website so up to date lately). Remember that Boxcar ended up a parallelogram last Motorama when I ran into Big Cookie one too many times. So, that frame went into the machine shop recycling bin, which meant I had to bash together a new one.

Luckily for me, Boxcar was assembled solely using the drops shelf at the local Metal Kroger. I had no plans to change the dimensions or do anything different, just pop out a spare. I just cut another few feet off the nearly full sized channel and tube I bought in like 2021 or something.

After the pieces were cut and the joints and cutouts machined, it was off to the …. uhh, bathroom to weld the corners together. Yes, this is why men take forever in the bathroom – we’re trying to knock out the last few welds.

(For one reason or another, the Internet gets very upset at the concept of the Welding Bathroom. I noticed a lot of people think this is my ONLY bathroom – which to be fair, would be very stereotypical terminally unmarried behavior)

After a new coat of “Detroit Diesel Green”, the color given to me at the start of this whole mess when I asked for the ugliest color paint the O’Reilly’s had on the shelf, I was in business. This brand new and shiny frame (and associated 3D printed eggplant) was just unceremoniously dropped on the still-working bot for Dragon Con in 2024, and it did alright – mostly making a big mess in the rumbles eggplanting all over everything.

At the end, I was down two drive motors and pretty much was just hobbling it around, which became part of the motivation for finally making it a “real” bot.

In fact, after it managed to somehow buckle the steel tube (granted, it was only 1/16″ wall), I found that the… uhh curvature of the member improved the impact posture. A lot of hammerbots do have some…. curvature in the member for a better impact angle against an opponent, within a range of heights. Maybe I’ll just keep this design as intentional in the future.

And so, Boxcar sat on the robot cruft room shelf after Dragon Con 2024 while I simmered over the redesign. Some of this build happened over the winter months, the rest (mostly related to the chassis) got bundled up closer to the con, but for presentation I’ll organize the steps in a reasonable narrative order.

It’s always a pleasant day when you get SendCutSend Christmas and it’s not Actual Christmas. I’ve been spoiled by SCS for work purposes now for a long time, but haven’t yet made much for myself!

SCS and friends basically changed the landscape of engineering design work by putting a fast food menu of high-precision sheet metal ops right in front of you. There’s basically no more excuses. For work, I’ve made gaggles of sheet metal enclosures and bracketree that mated up and aligned with almost billet machined part levels of prevision.

This is in stark contrast with my years of experience with sheet metal layout and farmout long ago. Even worse is if I have to run the brake press myself, because I guarantee that no two bend lines will be parallel, no radius and flange height consistent, and no two angles congruent. I was “afraid of” sheet metal and hybrid sheet metal designs for the longest time because of this. That changed with this build, when I finally had to set up my Sheet Metal workflow and design rules at home.

Alongside the main DeWut mounting crossmember, I had the sprockets and gears popped out of 3/16″ aluminum. Laser cutting precision has also come a long way too – those 12 pitch gears mated perfectly out of the box with one of 30Hauls’ old waterjet-cut 1/2″ aluminum gears.

Before I could get assembling, I had to conquer a side quest boss. The “brushless DeWut” conversion of course needed me to pull the pinion geas off the OEM DeWalt 18V motors. This has been a notoriously difficult exercise because of the design of the motor nose plate, which hides the backside of the pinion and largely prevents you from using any kind of off the shelf gear puller.

So I was going to cook up a custom puller, made from a block of steel with just the right dimensions to grab the DeWalt motor pinion.

I milled a channel into the 1″ steel cube and opened the bottom up in stages with a T-slot mill.

This is the principle here. The top of the T-slot channel grabs the pinion just inside of the teeth, whereas most gear pullers need to wrap around the motor shaft.

I used a #8 alloy steel socket cap screw as the driver. If that seems a bit undersized, it’s because it IS (for the amount of force people told me it can need), but it was the largest diameter screw that would natively fit inside the 5mm pinion bore. I just compensated some by giving it a 3x diameter thread length, so maybe I’d just twist it off before it blew its own threads off.

It worked extremely well in the end, because… well, it actually didn’t need that much drive screw force. I think because so few people have ever pulled DeWalt pinions, the operation maybe reached some kind of mythical, oral legend status among the builder community. I basically found out that the cyclops was actually an aggressive meat-eating rabbit – still fearsome, but not as big of a deal.

And with that, I salvaged pinions off two of my leftover DeWalt motors and was ready to assemble the 42mm brushless motors on them. They were pressed back on with green Loctite 609 retaining compound.

The finished product! Everything went together without issue, since the replacement motor mounting block was designed to be the right depth to use the OEM standard 42mm motor shaft length, without cutting or grinding anything.

Next up, I worked on crafting the new geared lifter/eggplanter hub. I needed to clean up the laser-cut bores of the main lift gear laminations, which was a quick boring (literally) operation. I just declared Law of Averages here and stuffed a bunch of gear slices in the chuck, figuring it had enough teeth engaging with the chuck to kind of sort things out concentricity-wise. Somewhere, my old Machine Design professor suddenly grabs his temples and screams.

The hub itself is a chunk of thick-walled steel tube stock that I put two big snap ring grooves and a 3/8″ keyway into – it matches the dimensions of a 1.5″ standard keyed shaft. It gets welded to a thick-walled 1.5″ square tube which the smaller 1″ whatever i put on the bot gets bolted into.

Back from the welding bathroom, I added a large chamfer to give clearance to the DeWut as the assembly rotates.

This is the completed hub after welding and processing, with the gear slices stacked on. The slices are retained on both sides by a big 1.5″ snap ring, applied using the most terrifying snap ring pliers I’ve ever had to use, which I picked up for Stance Stance Revolution previously.

That was a double face protection moment – safety glasses under the whole-face shield. Luckily, I only shot it off one time!

Moving onto drivetrain assembly, all of the drive sprockets got an edge chamfer using a quickly-made mandrel.

The drive assemblies are pretty straightforward, with the hubs and tires built the same way I’d been making them (though these days I just incorporate the little adhesive-and-torque-promoting blades into the hub itself). Eight plastite type self-threading screws, probably overkill but an easy number to count to, hold the sprockets onto the plastic hubs.

Now we’re getting into the heat of the build with chassis work! I picked up a 38mm Forstner cutter to cleanly make a hole through the UHMW frame rails – a regular hole saw would have been fine too, but the closeness of the tie rods holding the gearbox together made me want closer tolerances than a hole saw would manage. The P81 ring gears are a little under 1.5″ in diameter, making the 38mm hole a light slip fit.

I made drawings and drove the mill myself like some kind of 20th-century scrub.

Very quickly, the bot reached the integration stage of the build. In the grand scheme of things I build, this is probably one of the most brain dead simple things, which is quite nice for a change. It means it should keep working. Right?

While the machining was happening, the Main Bracket™ was finishing being squirted out of TPU. Much like Main Brackets of yore, it holds the battery in the rear pocket and the ESCs up front. The “power switch” is the good ol’ just unplug the battery (pretty much banned everywhere now, I think) but Dragon Con badger don’t give a fuck.

And really… that’s about it for the mechanicals of this bot! The drive chains started out very tight because of the unfinished edges of the sprockets, combined with my “Ideal Center Distance Plus Like 5 Thou” spacing of the axles. They’ll find each other over time.

Wiring was largely ported over from the previous build with some connector changes and splices. The Brushless Rages are the size of suitcases compared to modern AM32 controllers and made wiring more difficult than it had to be. I did pick up a slew of sample AM32 ESCs off a few vendors after Dragon Con, so it’ll be part of the future changes to mess around with them and see which ones I like.

Boxcar 2025’s test drive was simply me bringing it to the con on Sunday and driving it around with an advertising message written on it! I went around menacing the other droids and R/C models. By the end of the day, everything had “worn in” enough to be smooth. So this thing was fight ready for Monday!

Here’s the “press photo” of the 2025 bot. At the Robot Battles on monday, it started becoming a new meme with the audience repeatedly chanting “EGGPLANT” whenever it was on stage. It left the event working, and would be entered almost unchanged in Motorama 2026…

i put dro on my mill

chorl

Some time last year, I bought a mill. I then proceeded to drive that mill solely by eye, backlash-riddled dials, and Sharpie marks forever and ever, like I was doing for a while as a plucky undergraduate. While pushing around, on the bench, the DRO kit that I bought not long after the mill. Vacuuming around it, carefully arranging workpieces around the kit, for the better part of a year.

Alright, I’m finally sick of doing that! With the weather being too cold again for me to want to work on the van piles, and Motorama around the corner again, I’m just gonna sit down and bang it all out over a few days. There’s a couple of parts I needed to fab up for the new Susquehanna Boxcar, for instance, not to mention a new 30Haul build (finally)!

So here’s what we’re looking at. It’s a generic eBay scale kit with display that comes in a few sizes, and I picked two that are a little over the axis travel lengths. I chose to not integrate a Z-axis column readout (the usual 3-axis kit) because the quill has a little readout on it already.

I’m taking the slightly unusual step of mounting the X axis scale on the front of the bed. Usually, you’re supposed to mount them on the back of the bed, but this takes over an inch off the Y-axis travel. On a small machine, I would prefer to retain as much travel as I could.

Instead, I’m going to make some Bracketry to hang it off the front of the bed. I mean, not that ANY of the supplied generic aluminum channel/angle brackets fit this setup, since they are all cut for approximately Bridgeport-sized machines.

In positioning the scale at the front of the bed, I would have the issue of the scale and slide running into the Y-axis handwheel. But it turns out, you get approximately a free 3/4″ of additional travel simply by unscrewing the leadscrew mounting block from the front of the machine.

This standoff distance is the limit of full axial engagement of the leadscrew nut (mounted to the saddle) when the table is all the way at the back of the machine, so it’s not like at that point I made the thing hang on by one thread pitch. I simply used the extra screw length they already gave you!

And just like that, an extra 18mm of travel is bought for the price of two steel spacers.

This wasn’t a precision surface here anyway, given that they powder coated it over. The “bonus” travel meant that only the readout slide would overhang the handwheel by a small amount, when the table is fully bottomed out towards the front of the machine, instead of the whole scale mashing into it.

Other than that, installation of the X axis scale was fairly straightforward. I just lined up the bottom of the scale with the bottom of the table. A T-slot nut resides inside the mounting blocks, and the hole is slotted to give about 4mm of vertical slop tuning. It’s going to be a tighten-once affair anyhow.

Now I had a solid look at where the slide will end up, and can design a small Bracketry to connect this to the saddle. The gap between the slide and Y-axis handwheel is about 3mm in the center.

I got a start doing the same kind of size-up operation for the Y-axis scale. This one was going to be pretty awkward. The plan is to mount it at an angle on the side of the machine, but there’s not any good gauging surfaces to line it up. So, with some little welding magnets supporting it and a bubble level on the table surface, I got it to a place I thought would be the most ergonomic to fit up the Bracketry……. and hit the ends with a little bit of spraypaint to transfer the mounting pattern.

I then center-found the paint stains and drilled into the casting. I mean, the slots are there for adjustment, right!? As long as I wasn’t too far off on a length basis, the exact up-and-down placement isn’t too important now.

That actually worked way better than I expected. The same 18mm spacers stand off the scale from the machine. Now I had a few good gauging points to work with for making measurements. Usually, DRO slides are mounted with some thin, (relatively) flexible metal leaves and brackets to not transfer much force along the scales. I was just going to selectively 3D print them, so they’ll be inherently a little flexible.

I moved onto doing the rest of the machine setup and oh my goodness you guys didn’t even TRY to line this up. I was legitimately unsure if the arm was meant to be mounted at some awkward angle, but ultimately I think these holes were supposed to line up…

Nothing a little force on the drill press can’t accomplish. The arm mountnig bracket is also drilled and tapped into the column casting.

Now onto the Bracketry! Here is the proto-form of the X-axis slide bracket, made entirely to measured dimensions. The two mounting holes natively exist on the machine; they were to mount a little stopper/pointer at the center of the saddle. I’m just hijacking them to mount the readout slide.

With a little more prodding and an afternoon print using carbon fiber filled nylon, the test fitup went very successfully! I didn’t really need to make any changes at all here. Notice the shim washers between the slide body and the bracket. I purchased washers of the right thickness to make up the thickness difference between the slide and the scale. I suppose they could have been “printed in” but I wanted the fine tuning.

And here is the finished X-axis scale. The table is shown at its maximum travel towards me, so as promised, the slide overhangs the handle just a tiny bit, but is accommodate by the cutout in the Bracketry.

I later went back and made a second revision to add a little more rigidity. I remade this using the same CF Nylon, but added a post-print heat treat to increase its rigidity even more. I’m highly confident this is at least as good as a chintzy 2.5mm thick recycled beer can aluminum flap.

Next up, I used a jig to drill a similar set of spaced mounting holes into the saddle to accommodate the Y-axis slide.

Now this thing was a lot more awkward to measure. The dimensions shown in the sketch are essentially the dimensions I took IRL with calipers, gauge/setup blocks, and so on. The bracket had to reach a little up and over the scale body, then drop down to hang the slide. I 3D printed this exact model to do visual checks, and ended up blasting out 2 revisions in PLA. This sounds like it might have taken forever, but with modern high-speeders like my Creality K2+, each Rev was really just like 20 minutes.

When I liked the fit, things got more serious and… a little weirder looking. This final revision was also made in carbon fiber filled nylon. It’s secured to the saddle with two screws wearing fat washers, and features four curving ribs to give it rigidity as it does the ol’ reacharound.

Very happy with how this turned out, as the slide barely clears everything yet remains fully aligned through its whole travel.

Not only that, but it was designed to accommodate the X-axis leadscrew and table endcaps. This is the farthest the table will crank that-a-away, and the leadscrew bearing bumps are just a few millimeters away from the Bracketry!

And there we have it. Suddenly this thing became 10 times as useful (or me 10 times as lazy). But at least it means I can bust out robot particulates even quicker!