The Susquehanna Boxcar: A Return to Motorama

For literally over a decade now, Motorama and the NERC Robot Conflict event associated with it has been a sort of winter robotting tradition for me, minus only a few years; in 2020, I was in the middle of moving and so didn’t go back north for a while, and there was no Motorama in 2021 for Reasons.

However, the last time I really fielded a bot was in 2018 with the outgoing 30haul; I just went in 2019 for funsies and to help out. This year, with the Reasons beginning to wind down and with everybody in the robotting community ready to get competitions going again, I decided to to take a break from vans and enter something again.

But I had one rule for myself: No spending money on the robot.

This bot, whatever it’s going to be, was just a short detour from Operation IDIocracy, and it was going to just be a shitpost entry. Cleaning all the grunge and getting the engine apart has taken longer than I was counting on, and on top of that, it’s cold so I kind of lose motivation to wrench on things. Robots can be done indoors.

I had to build this entry as much out of just the materials and parts in my midden. Screws are fine, buying motors and ESCs or ordering custom cut parts is not. So what am I going to make? Initially, I thought about an extremely dirt floor rendition of Stance Stance Revolution in a 30lber, maybe using lawn care blades as the weapons.

To this end, I have plenty of weapon motor candidates in the form of 40-60mm brushless motors from Overhaul. I actually had a “preview” sketch model of what the next SSR beetleweight was going to be:

Actual stanced wheels! I had a few bright ideas on how to drive those while I was mocking the design up. This is definitely going to happen at some point; however, now getting close to the new year, I was getting less inclined to make a 30lb SSR as it was looking like more and more effort. Effort was to be avoided.

So why not a 30lb Sadbot? After all, Sadbot is my most successful heavyweight. I had plenty of 3″ C channel and 1 x 3″ rectangular tube left over from Vantruck add-on candidates, which was perfectly half the size (height) of Sadbot’s 6 inch channel stock.

We begin with a master sketch of the outline of the bot which I used to drive Inventor’s “Frame Generator” design tool, which is more or less the equivalent of a Solidworks Weldment with its libraries of standardized profiles and extrusions.

Weight was going to be a serious concern; my first pass frame measured out at 21 pounds out of 30. So having the frame size be driven by placing components and easily adjustable was important. I was basically looking at stuffing a 12lber inside a ring of steel.

The chassis material inside the beltline was going to be good ol’ UHMW plastic, a staple of my high school, pre-machine tool building. It behaves like a very dense bowl of grits and is easily workable with woodworking and handheld tools. This was really shaping up to be some kind of accidental retro-build.

Adding to the retro vibe was picking some 18V mixed-heritage cheap drill motors out of my bucket of motors. I would occasionally over the years “sample” cheap cordless drills from Harbor Freight, Walmart, and the like, so I have probably over a dozen of these which are almost all interchangeable. The newest lithium battery models have been deviating from the classic conical gearbox shape as manufacturers try to make the drills smaller/lighter while having 2 speeds as a default option.

The drill motor is to actuate a pokey stick similar to sadbot, and I was planning on a simple chain drive to an axle above the frame.

For drive, I decided to keep digging through my motor pile and found some mild-wound 555 sized motors. They’re identical in size to the usual 550 size R/C car or truck motor (and drill motors) but are typically wound to run at higher voltages, like 24 volts. The ones I have are surplus from who knows when, and have a Kv of 450 RPM per volt (Compare this with the typical 1200 to 1500 of a 550 class drill motor). They can therefore be run with a single stage of open gears, trading speed for torque.

In this bot, space was more the issue than anything, and using a single-stage spur reduction let me push the motors into the UHMW frame rails to clean up space in the middle for the drill motor and eventual electronics

So why not brushless? Well, that would involve finding 4 matching motors and/or ESCs in this size range, which I didn’t have. And no spending money!

I began sizing up the gear drive using a 4 inch wheel as a reference, using the spacing of the 555 drive motors and the drill motors as a guide for what gear size I could use. I’m going to exercise some impure nostalgia here by just 3D printing the wheel and hub. The gear pitch is 24 DP (or about Module 1), since that’s what my 3D printer flock can consistently print and have it work out well.

Initially, I was designing this hub to use the same wheels that 30haul did, made using the same methods and having the same dimensions as the Vex hubs I was using – hence the 1″ nub sticking out of the gear. I was going to hole-saw some 1″ gum rubber sheets and retain them with standoffs in the manner of its “disposable” duallies.

However, on a trip to Harbor Freight, I serendipitously found a new avenue to explore…

My only real complaint about the gum rubber wheels for 30Haul was that the sheets don’t come in any thicker dimensions than 1″, at least not with my minimal familiarity with the rubber indutry. Ideally, I’d be able to get a single 3-4″ thick wad, or laminate a few sheets together and be able to cut out wheels for actual full-size Overhaul.

I could probably get away with running singles for this bot, but I’m also keeping an eye out for thick chunks of rubber foam. And I found it by accident at Harbor Freight in the form of what I call the “Harbor Freight Yoga Mat”, actually a kneeling pad. It’s part number 56572 (as of now, anyway). It’s kinda exactly what I wanted – a big slab of rigid-feeling EVA foam. The texture felt right to make into wheels, and if the traction wasn’t good enough by itself, certainly I could coat them in latex or silicone (a long time favored builder trick still in active use at BattleBots!) for more traction.

So I violated my own rule, as usual, and spent money on the robot. One Harbor Freight Yoga Mat, for science!

I started prints of the hub design on a Markforged Mark Two (hi Markforged!) as well as a new-to-me Creality Ender 3 V2 (hi Naomi Wu!) that I picked up for $40 in a “Curated Wreckage” state. The pink material is PETG, which is my preference these days for non-critical and experimental prints that nevertheless will be used in the final application, despite my denial.

Those slots in the gears were added for a wheel retention feature that I dreamed up as well, and which will be seen shortly.

One issue I ran into with making the gum rubber wheels for 30Haul was keeping the hole saws centered with respect to each other. I decided to tunnel my way through the problem this time by opening up the center bore of the 1″ hole saw to fit on the 4″ hole saw’s larger arbor thread.

These cheap hole saw sets aren’t hardened meaningfully, so I blasted the bore out to 16mm with a metric step drill I had. 5/8″ probably would have been fine also. After this, I was able to jam both of the hole saws onto the larger arbor!

It was then just a drill press job away from making wheels that were at least concentric one one side; I didn’t want to go buy 2″ deep hole saw for this, so I had to just flip the Harbor Freight Yoga Mat around and find the pilot hole.

Here is what the deal is with the six slots. I didn’t want to just adhere the surface of the foam to the printed hub face because I thought the foam was just a bit lacking in integrity and would separate under the “skin”. I decided to add some interference elements, not unlike the standoffs of 30Haul, but without the intention that I could take it apart again.

So out came these ABS trim strips I bought for something way back when. I decided to use them as quasi dowel pins or driving keys. They get cut into chunks, pressed into the hub, and then trimmed with scissos.

With six slits cut into the foam with a knife, I could press these in with adhesive covering every surface, thus ensuring that plenty of surface area grips the foam on the inside.

E6000 contact cement is my go-to for these kinds of robot shenanigans. I slathered each edge of the “blades” and the hub face with it, and left it to cure under a weight.

That’s what one wheel looks like. The next day, I was sufficiently satisfied with the roundness and rigidity, and hit the go button on 6 more wheel hubs.

Alright, experiment over. Time to flesh out the rest of the design. I needed the drill motor shaft to stick into the center of the bot, so I decided on just using some fat standoffs.

The drill motor is mounted in a slightly unusual but also traditional way, using 4 of the of ball bearing clutch holes as mounting holes (and the other 4 still serving as clutch ring locking holes). All of these holes are to be tapped #10-32. This approach is stronger than using the two very small #4-#6 holes in the nosecone area.

The poker weapon drive is as simple as it could be. I’m using the same tactic as I used on Sadbot’s latest poker: Just welding a steel tube to a sprocket. The center bore is made for a 5/8″ ID bushing, which will just be a drilled piece of Delrin plastic in a 3/4″ drilled hole. The sprocket I plucked out of my Tomb of the Unknown Power Transmission Part is a 30 tooth #25 size.

25 isn’t my go-to for lifter/hammer style weapon in a 30lber. I’d much prefer #35, but I only had very small sprockets in #35 at the time, and something something no spending money. The same applies to the 5/8″ shaft. I would prefer at least 3/4″, but had some 5/8″ 4130 chromoly tube that I figured would stand a better chance than thin-wall 3/4″ regular buttery steel.

One of the next things to settle was where to put the weapon axle. I ran through a few options for this, including having it in-line with the top surface of the frame and making a half round shaped clamp to hold the axle in place.

The “overkill V2” iteration is where I decided I also wanted the ability to tension the chain, so let’s make a fancy set of towers that have slots so I can slide it back and forth for tensioning purposes?!

The third and final iteration is the “No, that’s too much effort” revision, which was a compromise. I needed more space between the sprockets anyway, so the axle had to move up. I decided to just make a simple block mount from the same offcuts that the frame will be made from, and use shaft collars or spacers to retain it axially instead of clamping

And that….. is all the CAD that I did before starting to cut metal and plastic. After all, I had 95% of the parts in house and ready after searching around for the day.

The electronics of this thing were to be equally found-object. Namely, I “found” two brushed Ragebridges, and decided I was going to break up one of my knockoff 18V Milwaukee Fuel batteries, which contain 2500mAh 18650s. The “9Ah” knockoff contains 15 cells (5S3P) and so I was going to run 7S and make two packs out of the one battery.

Next up: Fabrication, then the Motorama trip!

Norwalk Havoc May 2021: Scale Model Testing Your BattleBots in Nightmare Mode

It’s time for robots once again! I think what I’m planning on doing from here is, barring one or two more Summer of Ven posts (which is now well into the Fall and Winter of Ven anyhow) I’m going to begin transitioning towards Overhaul, finally.

You see, a major over-winter project of mine was trying to get Overhaul 1 up and running again, at least walking. There was a good bit of fabrication and “What in the everloving fuck did we do here…” reverse engineering your own work from 6-odd years ago. While it’s cool enough in its own right, I’m planning on using that to move towards the long-overdue Overhaul 3 design and build series. I mean, y’all already know what the bot looks like since it’s appeared on here by now, but there was a lot of translation from 30haul’s geometry to the full size bot.

But in the mean time, let’s talk 30haul. Recall the “lessons learned” of the previous March Norwalk post

I’m revising the Snout design to be stiffer on the corners, trading the internal webs for a U-shaped bottom truss shape. The metal is rigid enough on this scale that I don’t think the center webs contributed much.

Next up, after watching enough Battlebots and seeing enough matches at this point, I’m going to make 30Haul an entry in the “fork wars” currently ravaging the combat robot landscape. The joke is that ground-scraping forks grew a foot over the course of the 2020 season, as one of the only ways to ensure a vertical spinner doesn’t get under you, is to get under it first. Keeping the opponent away and under control is just as essential as being able to take (or deliver) the hit…

I’m also beginning to like the Vex wheels less and less, because while they initially offered the bouncy compliance I was looking for, once they start disintegrating, they become more liabilities. The spokes will tear through, leaving the big gaps in the perimeter that then flap in the wind. I decided to try and find some thick foam rubber I can use to make at-scale foamy wheels, not dissimilar to Overhaul’s.

Before any of that can happen, though, I had to have a 30haul that was functional. The damage from March wasn’t that bad in the grand scheme of things, but in the name of thoroughness I decided to completely take the bot apart and remanufacture it to address some of the frame damage and retighten the motor screws, among other tasks.

So here’s 30haul in a pile of itself! I planned to repair the frame as much as I could and keep it around as a backup, because…

Prior to March, I commissioned an entire new chassis to be machined by Wedge Industries. I figured as long as I actually had new 30haul parts, why not just move the bot to the new chassis and keep the old one as the “Just in case…”

To save some expense, I had Alex pound out only the net shape geometry. Since I have my own capabilities, I save some on the machine time and setup when it comes to tapping and countersinking, among other operations. So the first order of business with this new chassis was just chucking the ol’ spiral-flute 1/4-20 into my drill and having a pleasant time.

To the old frame, I repaired the damaged threads in multiple frame rails with threadlocked Helicoil inserts. The rear bulkhead shown here was actually quite bent up from the Ripto match. I used my arbor press to straighten it using some cleverly placed spacers.

Original chassis coming back together with an added weight-shaving pocket that I designed into the one that was sent out for manufacturing. There’s nothing over this area worth hitting really, so no reason to have the weight.

And the original chassis fully repaired and assembled!

The new chassis needed the end-tap holes put in. The way to do this would be to set them up at an angle on the drill press, but I was confident enough in my drill bit rodeo skills such that I just clamped everything together on the bench and hit the front (angled irritatingly – that got designed out of Overhaul 3) bulkhead holes. The rear set I piloted and threaded in one screw before finishing the rest on the drill press.

New chassis fully assembled and ready for population.

Next item on the agenda was to make some wheels. I said earlier that I wanted actual foam rubber wheels for 30haul now to get away from the Vex wheels, as while they did offer the compliance I was looking for, their failure mode was becoming big rubber flaps.

I looked into a few difference sources of “rigid” foam rubber, such as anti-fatigue floor mats and similar. Ultimately McMaster-Carr came to the rescue with a sheet of natural rubber foam – the nice thing was, in the time I had, it just offered a compression/deflection rating in PSI so it was easier to visualize how much give it would have.

To manufacture the wheels, I initially tried to find a hole saw set where I could get a 4 inch and a 1 inch saw on the same arbor. Maybe this was possible in the ol’ glory days of Comedy Central Sports Presents BattleBots™ as I recall a few builders’ reports saying they mounted two hole saws on one arbor to cut washers (e.g. for clutches, spacers, and wheels as well). But these days the consumer systems seem to have evolved and specialized, so the smaller sizes of hole saw usually have direct screw-on mandrels and larger ones have the pin locking ones.

I ended up picking up probably the most horrible Chinesium hole saw set Amazon had to offer in the hopes that it had generic mandrels, but alas, I found that the D-bore of the saws were different sizes as well. Either way, I found out that just hole sawing into the rubber wasn’t bad for alignment anyway. It’ll become round once I do enough burnouts!

I drilled these wheels using the Vex hubs as a template and put the same hole pattern into them.

For now, I made only the two (well, four…) front wheel assemblies to alleviate the worst of the wheel compression issues. What would happen is the Vex wheels would flatten between spokes and then bounce up once it reaches a spoke, and it actually made the bot drive a little bouncy as a result. These are a good deal lighter than the Vex wheels as well.

Hey, no use in spending too much time making wheels if I don’t have the rest of the bot yet. So off we go with populating the new chassis!

While doing so, I re-discovered a problem that might have prevented 30haul from being able to lift much. Recall that I had to step down from a 3-stage P60 gearbox to a 2-stage because the torque of the 3-stage type was rounding off its own output spline. This design stands in contrast with Overhaul 2 (and 3) because 30haul doesn’t have an intermediate gear stage, the lift motor directly fiddles the Big Gear.

I noticed the motor would bind up whenever I spun the gearbox one way. It turns out the output spline on this gearbox was deformed helically in a fashion that positive torque (lift) tended to shove the carrier off the spline, causing it to bind up like a clutch plate against the first stage.

Well, to repair this, I’d just have to replace the output shaft. Trouble with that? To clear the Big Gear and lifter forks, I had to position the motor farther away from the sidewall with the support bearing. Namely, about 2 inches. The stock Banebots P61 gearbox has a 1.5″ shaft.

I was at a juncture where waiting for Banebots shafts to be ordered would mean delaying the bot’s assembly into the week of the event, which I really didn’t feel like doing. So I decided to make a shaft extender, just a turned piece of 7075 rod with a 1/2″ socket on one side and 1/2″ stub on the other, long enough to bridge the gap. A 10-32 screw goes through the middle into the end-tapped P61 shaft.

Here’s what it looks like installed, along with the rest of the motors. Again, the motivating factor here was just to be able to reach that outer support bearing with a stock-length P61 shaft, of which I have plenty of spares.

Wheels loaded on and chassis off the ground now. I like these front wheels already – they don’t cause the front of the bot to sag at all, but are still very bouncy. Boy I wish someone made 3-4″ thick chunks of this stuff!

I finished assembling the bot and put it in “Sportsman Mode” since I didn’t yet know who I was fighting at the time – I’ll change things once I get there. In the time between this and leaving for the event, I put together what I think are the last two 6-fet Brushless Rages left and readied some other spare parts.

You see, by checking out the registration roster, I found out that every other 30lber was a vertical spinner of some sort. Whether disc or drum, this tournament was going to be absolutely fucking brutal. Hence why the title is….

Scale Model Testing Your BattleBots in NIGHTMARE MODE

I teleported up to Norwalk over the course of the day on Friday, May 14th, and got to my (now usual…) Norwalk generic business hotel around 10pm. The event started at 9 the next morning, and it was a full house.

I started 30Haul out in the “sportsman mode” configuration anticipating needing to change out to anti-vert forks. I got “Hyperbite XL” as a first draw. It’s an homage to Deathroll from BattleBots, and luckily was very high off the ground, so I actually decided to roll with these. I was out to test a “Just reach out and grab it” strategy.

Hear me out here – pretty much every vertical weapon worth its mettle takes a few seconds to get up to dangerous speed. I’m content with declaring the clamp disposable and just going up to it and grabbing it. If they try to turn away to prevent this, so much the better.

Well I mean it kinda worked. The only downside of declaring the clamp arm disposable, is you better have a whole lot of them, which I… didn’t. So this was the outcome of “Just grab Hyperbite XL as it’s trying to spin up” – while I was able to keep it at bay, the buckling actually jammed the clamp motor so I couldn’t grab and lift so much as just toss around.

There’s no “stream clip” like some of the other matches, but the match is at 3:12:36 in the main stream recording.

Hyperbite XL managed to machine some of the tips off the forks and snap some of the threaded rods, all from the small amount of contact we made in the match. That’s the downside of fighting a modern vertical spinner – there’s so much power density that the damage slope is very steep. You can really just mess up once.

Nonetheless we were both thrilled enough with the outcome that we decided to call it “Overhaul vs. Death Roll”. See? Battlebots should just be 30lbers.

Great, one match in and I’m already on my spare clamp. I managed to hammer the other side of the first clamp (the half that didn’t become wall art) straight, just in case I had to use it again.

Of course, the next match was against Other Disko, which is a more traditional 4WD vert architecture and multiple-time champion of northeastern events. Great. Luckily, this meant i got to bust out some experimental “Vert Blockers”, extended forks that act as a ground-level push-me stick. There was a lot of fork and counter-fork action at BattleBots this past year, so I decided why not give it a try as well.

This one was fairly brutal and took a long time to recover from. The key takeaway is that Vert-away forks work until they don’t. I mean, the opening gambit was about the best I could hope for, and then it just became pear-shaped.

I think that’s my main beef against the KE meta, really. That because of brushless and lithium batteries, there’s no more compromises that need to be really made on that front. You can have a fast and maneuverable drive, a solid chassis, and an extremely effective weapon, so there’s little point in having anything else.

At one point 30haul must have gotten booped hard enough on the snoot to buckle the leadscrew that drives the clamp. Luckily I decided to actually cut one of these as a spare, or else I might have had to resort to being a lifter only!

(Maybe that would have been better….)

I next faced Marathon, which was an “Overhaul vs. Minotaur” moment, and I was rather pleased by the outcome except that Marathon was counted out under what we think were incorrect conditions. I was still manipulating it when they pulled up the countdown. I was extremely peeved to find that for some reason, perhaps due to accumulated damage and misalignment, that I couldn’t manage a lift after the grab – something was stalling out the lift motor.

(I would find out after the event when I tore the bot down that one of the matches before, likely Other Disko, had bent the lift shaft into a shallow U shape that was binding up if it had much load on it)

By this point, I’d basically run out of fork parts and standoffs, so I was just going into the last match against Stop Hitting Yourself in “With your shield, or upon it” mode. I think it was a little more “upon it” as the dual vertical disks slowly plucked the remaining wheels I had cobbled and assembled out of whatever still was kind of whole.

I mean, in the grand scheme of things, the extremely prototype-y nature of 30haul has been its downfall all along. I was more out to get the shape correct and get a feel for how it’ll drive instead of focusing on functionality, and it still ended up using a few legacy parts from 30hauls and Uberclockers past.

The most important thing was I got a lot (a whole lot, let me emphasize) of recon on how to handle the vertical spinner EDM party that is BattleBots. A lot of the design issues I didn’t like about this 30haul had already been changed on Overhaul well before now, so I got to leave Norwalk this time with some “hmm” lessons for Overhaul, such as….

  • Just grabbing the vert is a valid approach, as long as I can line it up or force them to turn away.
  • The clamp head and forks are considered disposable and will be both treated and duplicated as such.
  • Vert-away sticks work until they don’t, and I’m not sure I’m a judicious enough driver to use them effectively.

I never actually got to test the new “snout” spinner wedge, first because there weren’t any horiontal bar or shell weapons, and second because I just never finished welding it after seeing there weren’t any! To be fair, Stop Hitting Yourself had a horizontal component, which would have been trouble if they decided to use it against me.

Hey, at least a clean picture of 30Haul is on the NHRL hall of fame wall! I think this photo was actually taken during the February one I went to.

With this NHRL, this 30haul’s story comes to a close. Like I said, it well outlived its original purpose and I was just running against opponents with a whole slew of design handicaps. There will be another one in the future, probably not this year, as Overhaul itself is now my focus of attention. And of course the new one will have conversely back-propagated design elements from Overhaul 3!