It’s about two weeks before Motorama 2024! Plenty of time to finish a robot and test it and get to know it…. right!? Theoretically, most of this bot could just appear overnight after a bit of press play and walk away. We’ll see that it wasn’t THAT easy, but it was still a super streamlined build, with machined parts being made while the 3D printables were materializing.

As alluded to in the previous post, my Ender 3 has been the workhorse for making small power transmission parts. I don’t think I’ve bought a gear or pulley in a long time, except things like extruded pinion wire I used on Susquehanna Boxcar. I equipped this Ender 3 V2, a little outdated these days but perfectly functional and smooth, with a 0.2mm nozzle so it can really hit all of the smaller details in gears down to about 32 pitch (0.8 module) or timing belt pulleys down to roughly the 3mm HTD pitch.

I’ve tried things as small as 2mm GT and MXL, but they’re not that clean. So, much of my “all in house” mechanical work focuses on the larger sizes.

This build was an opportunity to bring the Markfrogs back online after sitting decrepitly in a corner forever after the big move. This thing here is basically a classic car – it’s technically a “Mark 1.75”, being in the chassis of a Markforged Mark One but the extruders and controller of a Mark Two.

It was provided to me as the original Overhaul 2 sponsorship package (that’s 2016 if you’re keeping track) and has produced basically all the bracketry for it and Overhaul 3!

So let’s just stuff some carbon fiber in it and GO! The Eiger slicer software has evolved a lot since I last used it a bunch, so the UI took some getting used to. I was able to use the 3D representation of the fiber laying to fiddle some dimensions on this weapon motor mount. Basically I wanted more perimeter loops of carbon fiber, so I had to adjust the wall thickness of the mounting hole area to let it run some lines through.

Here’s a visual test fit of the weapon motor bracket and the drive gears. Somehow, an almost 9 year old machine that’s been sitting mostly dormant the last handful of years and got thrown in a van and then into a corner just wakes up and pounds out a carbon fiber inlaid part.

While making very crunchy bearing sounds, too – those belt tensioners are facing a desperate deferred maintenance condition that I really need to address!

Most of my nylon filament was in abject condition, of course, having picked up a ton of moisture from sitting around. Even a closed container isn’t that weathertight in the long run! So I had to bake my nylon spools (and threw the dessicant packs in for kicks too, to refresh them). I ended remembered too late that gas ovens produce water vapor as a primary emission component and ended up simply steaming my nylon for over 24 hours.

So… uhh, oops. Slight delay in the build as I hunted down a small electric convection oven on Facebook Marketplace to use as my dedicated filament roaster (and future epoxy setter, urethane curer, and so on). Obviously this meant I had to roast each spool for about the same time to get them even remotely printable again…

My supplemental order of Aliexpress worm gears also showed up around this time. The bot will ultimately use 20 tooth gears (these are 30 tooth in the image) but things were cheap enough that I just ordered a small pile. There’s a nice drawer labeled “Gears and Gear Accessories” they can live in!

I designed a few different wheels for the bot as well and tried each design out. They differ in weight as well as philosophical approach. I started with a basic “solid” wheel that could be printed using a sparser infill. This lets the wheel act a bit as a damage sponge as the infill can crush in response to being hit. I also made a basic spoked wheel which weighs a bit less. It also did take less time to print, so I decided to press on with that design for now.

At the end of the week, here’s a pile of completed parts. I decided the weird t-nut pinion gear was not going to stay in the final bot before I ship out. It was definitely too flexible. It’ll do for some basic testing, though.

I merely made a revision to the gear design which used a large hollow bore I could press an aluminum round into and drill and tap like a normal human.

The next parts to arrive were the weapon discs from SendCutSend. I went ahead and ordered a pile of them as well. 10, to be precise. I’m hoping this bot design stays around for a bit or else I’ll have some interesting yard Frisbees.

The long print job was the unibody, which took something like 28 hours on the Mark 1.75. It was the machine I trusted to just blast through the job without poking it or adjusting it!

The completed chassis. It’s not made of Onyx – I can’t afford that stuff any more, so it’s instead just generic Microcenter carbon fiber filled whatever. Definitely smells like nylon, but it makes a substantially different sound when you tap on it and is slightly more flexible. Somehow, despite me putting the most shit-tier mystery filament into it, the print quality was impeccable.

(By the way – that stuff comes pre-wetted. I don’t know if they extrude and reel it up in a tropical rainforest or what, but 10+ hours of 90 celsius or more drying is needed before even TRYING. If you’re not warping the spool, it ain’t hot enough!)

The next op was to make the disk hubs. These are just made of small chunks of 2″ round aluminum. I had remnants of a thick-walled tube that could be quickly turned down and bored out to size.

In lieu of a mill, because over the winter I sold the Benchmaster, Master of Benches and HAVEN’T BOUGHT ANOTHER MILL YET I made several drilling jigs for the parts I’d typically use a mill for. These were dimensionally tuned to tightly grab or press onto the part. I use them only for spot drilling holes, then press them back off and finish the drilling operation without them.

I didn’t want to give up the Benchmaster, Master of Benches, but I cared more about having a quill and having DROs and longer travels than its historical value. So after putting it up for sale at an obnoxious price to deter most people, I got a message from a guy who has a small collection of antique machines who was interested in restoring it as part of his vintage shop. Naturally the sale value was much more reasonable than the obnoxious go-away price. Not trying to turn a profit on it so much as maybe pick up some tooling for the Future Robot Trap Mill.

I went ahead and made three hubs, two for immediate use and one for if somehow an opponent reaches that deep into the bot. By that point I’m guessing the rest of it is hosed already, but…. good to have a backup nonetheless.

The disks interface to the hub using these four dowel pins pressed into the flange.

For the weapon shaft mounting blocks, I did the same get-jiggy-with-it operation on a chunk of 1″ wide, 1/2″ thick aluminum bar. This jig manufactures two blocks. It contains the drilling pattern as well as two marks for where to saw it in half.

I made the driveshafts as planned – just turning a shoulder, snap ring groove, and partial shoulder onto a 3/8″ aluminum hex bar. The small shoulder is for the bottom shaft bearing, and the big bearing sits on the half-10mm-half-hex portion. The gears were drilled out for the 10mm bore, and I added two little dimples to let their set screws get a more positive grip.

I think if I were to do this over again, I’d just replace the screws entirely with a single 2-3mm roll pin or something and have less things that can wiggle loose.

It’s starting to look like some kind of weird clockwork mechanism now. The future double-ended motor shaft is made from lengths of 304 stainless steel which can be picked up in 3mm undersize precision ground fit. No need for the case-hardened linear bearing grade stuff here since the forces are relatively low!

The shafts are cut to slightly shorter than the total length between the chassis pockets that house its support bearings. Then I just move the worm gears to where I want them and marked locations to put small flats (using a Dremel) so the set screw on each can grip. This whole assembly was already so smooth that the gears could somehow backdrive if I turned them with some effort!

Motors prepped and being installed with the new shafts. This just involved pressing their stock ones out and maneuvering the new one in place.

The next item to arrive was the side plates from CNC Madness. This operation is hands down the cheapest way to get composite flat parts made quickly right now, and I leveraged their 3mm and 2mm carbon fiber for the weapon uprights. This took just under a week from when I hit the Order button.

All I needed to do was add the countersink holes and the bot was suddenly together! I chose to use large #10 thread-forming screws for plastic (“Plastites”, if you will) instead of heat-set or coarse tapping inserts. Keeps the weight down and gets the point across for the strength of the material I’m fastening into!

The wheels are retained by these wide-face E-clips. No screws here, everything is made of laziness.

After the worm gears were firmly secured by the side plates and lubed up, I found out they in fact could backdrive quite readily. I attribute this to floating the shafts on ball bearings so neither radial nor thrust force caused a bunch of extra friction!

Weapon assemblies undergoing final assembly! The ring gear is attached to the hub using eight countersunk screws, with the aluminum hub flange being threaded to accommodate. Overall, it’s quite a compact package. As I said before, the only thing I’d like to change here is backing down from the gigantic 6200 type bearings I already owned. At least this thing will never fail due to that!

The bot’s entered the “difficult to look at from any angle” stage of assembly here, and was mechanically completed the weekend before I left for Motorama.

The electronics of this thing were done dirty. The 660mAh 4S battery just sits in the cavity in the center designed for its size range and the bottom plate holds it all in. The ESCs are leftover SimonK AfroESC 12 amp units from forever ago, when I bought a few dozen and have slowly since used or given them away in various ways.

The receiver is just a shucked Hobbyking TR6Av2 (or FlySky FSR6B) receiver that I’ve used for… oh, I’m not sure, 13-14 years now? They’re somehow still around and being sold, and my transmitters still work! Odd to put it like that, because it would be equivalent to using a 1992 model radio in 2006 when I first could afford/switched to then-new Spektrum 2.4Ghz tech.

The power switch is a random Fingertech switch I’ve had forever. Everything’s just hot glued in place and point-to-point wired. It’ll basically be impossible to service!

As a last touch and nod to its cultural inspiration, I made some cringy heart rims for Stance Stance. I ended up only bringing these and the 5-spoke wheels to Motorama for weight issues.

Check out the finished product! I’m very proud of how this bot turned out. It looks very sharp and clean, in my opinion. I decided to not paint it in its usual magenta and blue for Motorama since I didn’t want to take everything again, but will do so for future events!

Here’s a video of the worm gear drive! At this point, the left side still had a bit of a sticky spot which I never quite figured out, but it went away with a lot of driving.

The handle is extremely linear and predictable, since the worm gears basically act as an amplifier for motor drag and braking. I was definitely satisfied with how it drove, but only the event can show how durable and reliable it is.

Why was I such a stickler for weight? Because this is what the thing ended up at~ That’s 0.4 ounces under the limit. It’s just so full of gear. Figurative AND literally! I’m actually not sure where it can get any lighter. Perhaps the weapon hub bearings will be a good start, because it’s very much two hard shells and a very creamy, soft center. I’d like to try and transfer some weight into protecting the front, rear, and bottom some more.

The rest of the week before I left for Motorama was spent putting some more of the spare parts together and some test driving dancing in the driveway. Altogether, Stance Stance Revolution 2 was a pretty clean and enjoyable build that needed some design thought to execute, but it wasn’t like I had to devote all four of my remaining brain cells to designing a mechanism or making some obnoxiously complex part. That…. is for a different build coming soon.

Alright! Picking up from the last episode of stance, I was beginning to embark on the hyperfixation stage of designing. Basically, spitting things into a CAD model isn’t the part that really takes me forever (unless the model is extremely detailed or need simulation, I suppose) but the initial ideation and concept stone-turning.

A lot of this is just done by staring at the ceiling blankly for a while, or mulling over while I drive some place – much of the reason I seemingly enjoy driving up and down the entire Eastern Seaboard. When I taught 2.00Gokart, I called this “Grounding the design” in my lectures. It’s always easier once things condense because you start having actual dimensions and requirements and such!

For Stance, I started with a rudimentary driveshaft design for the worm gears to get some dimensions to work with. Next, I started hollowing the “block” out in a way that I can adjust the placement as the needs evolve. This took a few back and forths of moving the worm gear socket around (and changing its depth) as I dug up bearings I could use.

One of the first headaches from the brainstorming and cartoon model poking was the wheels. As mentioned previously, if I actually wanted to make 45 degree conical wheels, they had to get large. This to me seemed like a questionable benefit at best and a weight penalty pretty much by default.

To press on with the design, I decided to make a set of O-ring wheels like I have done for many bots before. These wheels will be used with soft (50A durometer) O-rings so they have some semblance of traction and shock absorption. If I found out I had weight or space later, maybe I’ll revise this to be a set of cut foam wheels.

Unusually, the O-ring groove was biased towards one side because they’re going to be touching the ground on the 45 degree. The “outside” was heavily flanged and the “inside” not so much. I usually specify O-ring wheels with a roughly 10% ‘stretch” so they don’t just flop off – this means specifying, for instance, a 2-3/4″ center circle O-ring for a 3 inch center circle wheel (which might end up around 3-3/16″ or so on the outside.

The bore was modeled as a hex shape with corner knockouts to prevent material bunching from the 3D print process affecting how the shape fits on the shaft.

i’m adding more sockets, caves, and spider holes for everything else here. The motor will sit in the middle between the two wheels and I’ll need to buy some shaft stock to make an extra-extra long dual shaft. No biggie there. On the ends with the worm screws, the shafts will ride in 3mm bearings embedded into the print.

With 3mm, 6mm, 8mm, and 10mm bearings already specified and it doesn’t even look like a robot yet, this is looking like it’ll become another Roll Cake or something. I can no longer design a bot that doesn’t use 57 tiny little ball bearings.

I’m choosing to retain the wheels with some “Poodle clips” or wide-shoulder E-clips, instead of a screw or nut and bolt setup. This will let me pop the wheels off quickly if need be, or… THEY’LL POP OFF QUICKLY IF NEED BE.

At this point, I was still entertaining the thought of the bot being made as two fully independent halves, which will be retained by some method. I started down the road of a dual dovetail joint retained by a pin doing down the longitudinal centerline, almost like a big Anderson PowerPole connector.

I’ve modeled stand-in side plates for mounting the weapon hubs here. They’ll change as needed later, and were for now just defined using the chassis “block” geometry.

I had enough of the design together to now make some comparisons to original Stance Stance. It occupies the same rough footprint, but the weapons are heavier and smaller in diameter (largely as a response to the modern meta of compact vertical spinners) and it has a lot more invested in the drivetrain. Stance Stance Revolution 1 used only two Fingertech Silver Spark motors for drive. How it was even able to move, I have no real idea.

Check out the preliminary weapon mount design as well. Two blocks, sandwiching the sidewall in the middle, with a single large shoulder bolt or similar running through it. The blocks will be attached to both sidewalls for rigidity.

It was also time to de-cartoon the blades, which were at first made for the visual only. I kept the basic shape, but I designed the counterweight side more functionally and used it to tune the center of mass.

Realistically, once you get within the 0.01″ mark…. I don’t think you’re even going to notice the benefits. Manufacturing tolerances alone will make any more precision not matter, and definitely the first few hits will ruin whatever you had going for you anyway. I got lucky and within a few “iterations” of changing the counterweight radius and angle, got the center axis to with 0.002″ of the coordinate frame.

I cooked up a hub to hold two 10mm bore type 6200 bearings. Severely overkill, but I already owned several. I probably could have saved a bit of weight here and used the smaller 6000 type bearing. The drive engagement is with 4 dowel pins on the inside of the blade bore (not visible here).

The best part? The weapon retainment is also with a snap ring. A very large, beefy one, mind you, at 2 inches in diameter.

The CAD has reached the “Hard to look at without vomiting ” stage at this point. I mushed a few dimensions around to optimize for both weight, which was becoming a concern, and serviceability (such as tool access, how to drop a part without also dropping 5 other parts, etc).

It was around here that I decided to backtrack significantly and get rid of the “Must be able to split in half in the funniest way” design. The center wall took up very precious space in a small bot and I was unable to find a battery I found satisfactory to fit in the awkward remaining triangles. I simply backed the model up all the way to the beginning after the motor and gear sockets and removed the big angled cut. Some very very angry assembly mates later…

I blew up everything more recent than the cut and started by emptying out the center of the chassis. It was kind of a manual Shell operation, because the actual Shell operation was too complex to drive all the custom thicknesses and skip/ignore-this-area demands.

As it was going to be 3D printed anyways, I wasn’t extremely concerned with excessive solid areas but did want to try and expose as much “perimeter” as I could, as well as get ahead on making space to mount internal parts.

More details going into the frame now. I added a center cage to hold the battery I had in mind, a 850mAh 4S that I had one of and bought another of. I also added a serviceability change, which was ensuring the motor and worm assembly can be removed as one.

The support bearing sockets were turned into a mild snap-in-place socket shape, such that the flexibility of the plastic let me push the bearings past them but the socket shape otherwise keeps them braced against the gear driving load. The motor mounting flange was “cut open” and I’ll only use two screws to hang onto the motor. This was done so I could avoid needing to untighten the worms in order to dismantle the drivetrain – I could, in principle, make 4 or 5 of the same motor-and-dual-worm assembly and swap any in and out.

Other features added by now include fastening holes for the side plates, which will simply be attached using Plastite (thread-forming) screws. No heat-set inserts, no backing nuts, no helicoils. Just big threads.

Weight was well beyond a concern by this stage. I had to change the thicknesses and dimensions of several parts a few times.

Originally designed to be 3/16″ thick, the discs had to become 1/8″ thick AR500 steel. I changed weapon motors to 2830 sizes because the two 2836 size 450 helicopter motors were going to be too heavy by almost an ounce apiece.

The battery mentioned earlier was revised from 1000mAh to 850mAh for the same reason, and I ended up buying titanium bolts for the weapon shafts instead of steel.

im not going to spend money on this robot

The weapon drive itself was kind of a detail left for last, because there was really only 1 choice given the placement of everything. That was gear drive. Gear driven weapons are relatively rare because most people can locate the motors sensibly, but when you are this close….

Now, belt drive does have its advantages still even at this close-in distance because of shock absorption. To counter that, simply make the gears B I G G E. I designed these as metric Module 1.5 (or about 16 DP) in case I wanted to use a pre-made pinion. The big ring gear would be 3D printed from nylon and fastened to the blade hub’s back using a bolt pattern, shown above.

One of the “blocks” that held the weapon shaft bolt was turned into more of a spoon shape with an integrated motor mount flange. I decided this was going to be more rigid and position-determinate versus having the motor flange cut into the side plates and the weapon shaft bolt blocks being completely separate.

While specifying the gear stock I was going to make the pinions from, I also decided to make a quick dumb version that was to be 3D printed from nylon as well, but had a set screw hub using two backing nuts stuffed into a socket.

I wasn’t sure if this was going to make it into the final version, since I think I’d rather have some solid metal in a weapon drive hub. But it would allow me to just bang the weapon drive out quickly and test it. And it wouldn’t hurt to have around as spares anyway!

After the weapon drive gears were finalized, I massaged the mounting bracket a little more to allow for easier service access.

As a last touch, because I did this many, MANY times during the design process… I indicated which way on the bot was the front. Many patterns and mirrors were lost to doing it on the wrong end! I’ve also done a bit of weight reduction here, cutting away more areas of the material which will be covered up by the side plates anyway so I didn’t need any more plastic there. Alignment cutouts for the bottom and top plates can also be seen.

And finally, the completed design!

Those side and top & bottom cover plates are going to be made from carbon fiber made by CNCMadness. The discs will be from SendCutSend. I just about don’t have to lift a damn finger on this bot except to make the aluminum weapon hubs and the driveshafts!

From here, it was “Watch my Ender 3/5s do all the work”! On the next episode of Stance, the Buildening…