Archive for the 'Done!' Category

 

Late Stage #PostmodernRobotics: Welcome to Your Waifu is Trash, the Robot Dumpster Fire

Sep 14, 2019 in your waifu is trash

Now that there is an #BrandNewSentence.

Ladies and gentlehams, this is a Golden Dumpster.

It’s several things. First, it’s the prize if you win the Norwalk Havoc event held roughly monthly at the 50Day Makerspace in Norwalk, CT.

Second, it’s a repainted Dumpsty desktop dumpster. No, this is not a joke; someone’s real life job in a shop and assembly room somewhere is manufacturing tiny dumpsters for consumption by edgy postmodernists everywhere.

Third, it’s about to be digitized and turned into a robot for Dragon Con.

Yes, this is truly the state of combat robotics today. This is what we’ve become, when all of the Ampflow brushes have melted away and all of the poorly-restrained Li-poly batteries have vaporized, the essential oil of the Harbor Freight drill gearbox. Welcome to #PostmodernRobotics.

So alright, what’s the actual story here? This is starting to feel a little bit like Stance Stance Revolution or Colsonbot.

In a way, it kind of is in the vein of those two. They’re all supposed to take the super cereal sport and turn some element of it upside down for entertainment. As you know, I tend to complain about how overly tryhard the sport has become especially with folks getting into the sport only building spinners (or worse…. only operating the same spinner for the better part of a decade) and focusing on win counts at rigid tournaments. Not that I have a strong moral basis to stand on here, since I obviously had my own era of “tryharding”. But regardless, in the position I am, I might as well keep at injecting whimsy wherever I can!

This dumpster is actually Jamison’s – not mine. I only took Roll Cake to one Norwalk Havoc event for kicks (where it did disturbingly well in a rumble, more than I expected by far!). It was bequeathed to me while Sawblaze was in temporary storage at Big Chuck’s Auto Body – you can kind of see it peek out in the background of a few photos.

Basically, we both wanted to see an assbot made for Dragon Con. With the time horizon for rebuilding Überclocker/30-haul vanishing, I decided to punt on the project instead of rush it (see, I’ve learned SOMETHING about project and scope management) and focus on putting on a show for the convention.

Obviously it was going to be almost completely ineffective as an entry – that was kind of the point. It’s too small to put any really worthwhile drive power in, at least not without actual engineering effort, and the dumpster itself actually weighs close to 8 pounds – it’s not a plastic shell, it’s actually stamped and welded steel sheet (speaking of engineering effort for questionable ends…).

My “goals” (???) for this build condensed as I was buttoning up Vantruck lighting. It was going to have powered flipping lids actuated by servos, and an internal vape system to emit a lot of thick smoke. I was just going to drive it around the convention as a neutral political statement – you can project any insecurity you want upon it! It doesn’t mean anything and nothing matters! True #Postmodernism!

 

I made it a curiosity goal to see if I could get it to “self right” with a linkage that allowed the lid to extend far enough. Granted, it can only ever self-right from one face only, so how much would it really matter? Does anything actually matter?

After a couple of iterations, I found a good enough solution where a 120 degree servo travel was enough to get about 200 degrees of output travel. The linkage consisting of the servo crank arm, the lid, and the coupler link in between basically was almost toggling at both ends (very folded one way or another), but was much more squared up when the lid was vertical, or when it would have the apply the most force to “get up”.

I was going to need a hefty servo – probably a 1/4-scale size – to do this motion anyway, so I was browsing for candidates as this process was happening. The short turnaround time before I was leaving kind of mandated a Jeff Bezos Special, and I ended up just going with one of these generic “60 kg” servos. No, they don’t weigh 60 kilograms, but allegedly put out up to 60 kgf-cm of torque. Do they actually? Who knows?!

They come in 180 and 270 degree travel varieties for different applications, with the latter being more rare, so I constrained the design to use the 180 degree type only just in case I had to find a spare. Always be prepared to quickly service your miniature flaming dumpster?

I was going to keep the drivetrain simple, using some 25mm diameter Pololu gearmotors I’ve had since forever. The “25mm diameter gearmotor with a centered shaft” seems to be a very commoditized motor form factor, and many generics exist and are popular with beetleweight (3lb) builders. Pololu sells a “HP” line which uses a hotter-wound motor that pulls more power, whereas the common ones on eBay and Amazon are very tame.

The drive layout was going to be 4 individual modules, with 4WD. Instead of just slinging a robot frame under the dumpster (sorry, I can’t take myself seriously typing that), which would pretty much guarantee it tipping over all the time, I wanted to hide the drivetrain within the bottom by making flange-mounted modules that attach to cutouts.

The drive bits itself are just four machined aluminum hex hubs for 1.625″ Banebots wheels I had on hand – dating all the way back to #CandyPaintAndGoldTeeth (which is a bot that REALLY could use a reboot!), and the motors are clamped in place with a U-shaped block.

I made sure to add an external support bearing for the wheels, since these motors do not have all that much output shaft support; one of the ways they get broken easily in battle is just by applying too much force to a directly-coupled wheel. They really should get external support, even in beetleweights (some get away with it using very soft and foamy wheels like Lite Flites), and definitely in anything heavier.

Here’s what it’ll look like from the bottom. The wheels are basically pushed out as far as they can go into the corners for …. stability. Yeah, stability!

I made the rest of the linkages based off the skeleton sketch model. By this point, I actually got the “60kg” servo in house, so I measured up its stock arm and designed a linkage to be sunken into it (for maximum torque transfer if this thing really can push 60 kgf-cm, I didn’t want to just rely on 2 or 3 screws)

And here we have the more-or-less final design, minus a few electronics detailed which were mostly freelanced as the build progressed.  Let fabrication commence!

Making the cutouts in the bottom of the …. dumpster … was actually more strenuous than I thought. This thing is straight up made of 18 gauge steel all around. Thicker than most Mikuvan body panels, as terrifying as that sounds. I used a Dremel with an abrasive wheel to make the cuts, then used a 3D printed prototype of the motor module as a drilling template.

These components are 3D printed in Markforged Onyx, a part of this balanced breakfast. The wheel outer bearings are thin-section Inch bearings I got a long time ago for Roll Cake – they’re type R1212, 1/2″ bore 3/4″ OD and 5/32″ thick. I rather like them for doing little inch-centric quick projects, such as this one!

Four of the motor modules assembled together. This is a very formidable beetleweight drivetrain, all things considered.

I went just maybe a little nuts on engineering a flaming dumpster by making the servo linkages all use ball bearing pivots. Seriously?! Yes – when you build a complex bot like Roll Cake, you end up with a million little bearings you bought but don’t end up using, and can peruse through later.

These bearings are type SMF83 – 3mm bore, 6mm OD, and flanged. They’ll ride on 3mm shoulder screws (also left over from Roll Cake iterations). Ball bearing pivots reduce the friction of linkage joints by a good order of magnitude or more, and reduce slop since they don’t need to have inherently loose fits – for a linkage as edgily-designed on the verge of toggling as the lid, I figured it would be a nice touch.

There are a couple of little 3D printing tricks that I’d like to point out. They’re not too visible in these photos, so it’s easier to show a CAD screenshot:

Basically every part on this bot is printed at an angle with the part not oriented “flat” like what’s common. I started doing this years ago, probably by accident while trying to print an awkward part, and realized it confers a lot of advantages.

First, you can distribute a load on a 3D printed parts in all 3 planes by tilting the part – at least going from one plane of loading to two.

In a part that has multiple orthoginal axes of pin joints or screw holes, instead of extremely compromising on the strength of one axis by forcing it to be loaded “between Z layers” where deposition modeling is the weakest, you effectively slice the part to include them in a skewed fashion.

That way, for example, my pin joints and bolt holes are all grabbing material on the 45 degree plane, each capturing many layers of material – clever part design with this in mind can even result in fasteners that capture the entire width and length of parts. This approach also makes 3D printing embedded trusses and other lightweighting shapes more effective for the same reason: the geometry permits material stress transfer into more planes and axes at once.

Second, by tilting some features, you can avoid support lattices in hard to reach places or which would cause poor finishes in a precision-requiring area. A lot of the parts were printed without support, only a “brim” on the lower 3-5 layers to promote adhesion.

The downside is your printer has to be in good tune to do this, since it involves printing almost exclusively in 45-ish degree overhangs and support lattices generated may be much smaller. I trust the Markforged machines to do it – a tunable RepRap-family printer might need some intensive training beforehand.

The electrical deck was freehanded from a sheet of 1/8″ Garolite, and the battery cradles and clamp designed up and thrown on print also. I designed around a set of 4S, 1.8Ah packs I already had, but made sure the cradle was big enough to support the next size up like a 2.2Ah or even 3.0Ah for longer run time. Remember, I was out to drive this thing around for the better part of a day, so it’s carrying about 4x the amount I would ever expect a beetleweight drivetrain to use in one match already.

While this was all happening, I was also waiting on paint to dry. Because of course I will make it Miku-colored!

I ran into some serious issues with painting it, though – the Golden Dumpster is in fact made from painting gold over a regular green dumpster, which is green paint over the bare steel. So I was adding shitty spraypaint on shitty spraypaint on more shitty spraypaint. Some of it started crinking up and detaching in chunks, which was unfortunate. I decided to just forget about appearances – a weathered dumpster with chipping paint and dents just sells the story!

Anyways, here’s the motor pods and electroncis deck dropped in and screwed shut.

The electrical system was actually a little bit of a conundrum. The big servo preferred 2S lithium voltages (7-9v or so), the drive motors were 12V rated so it’s best to run them at that or higher (hence the 4S battery chosen – 14.8V nominal). Most vapes run at only 1S (3.7V) or in that neighborhood. The receiver could take up to 12V in, but the Pololu R/C relay should stay around 5V for best reliability.

I ended up digging out an old adjustable BEC (R/C power supply) from the pile of robot electronics, which could be tuned to 7.2V, an old 6-cell nickel battery voltage. This would feed the vape power (and a mini air pump that is needed to actually push the vapor out with force) and the receiver. I tested the Pololu relay and inspected its diagram to see if there was anything that bad about running it on 7.2V instead of 5 – nothing ostensibly besides possibly overpowering the relay coil itself. Overall, 7.2V was a reasonable compromise for everything on board.

The BEC unit and Pololu R/C relay get globbed onto the electrical deck, next to the most overkill possible controller for this application… a spare RageBridge. Talk about being under-employed!

The smoke effects actually got super interesting. What you see here is two CosCloud units provided to me by their creator Alina. They actually figured all of this conundrum out for me (and you too! and many others!). I was otherwise going to a literal vape shop to buy literal vaping gear to make my own.

I’ll be running two of these “smoke generators” in series to line up with 7.2V pretty well, and the air pump in parallel with that group. This whole assemblage drew around 3 amps at Full Vape, which was quite tolerable with the 10A-rated BEC.

The final packaging and zip-tying now commences.

And here’s what it looks like from the outside! The final weight – 11 pounds 8.8 ounces. Hey, there’s room for a… weapon?

The dwarf dumpster fire, in its natural habitat.

And what it looks like in action at the convention. The secret is to turn on the Vape Turbopumps for a few seconds, then open the lid and watch it all waft out. This thing was an absolute riot everywhere it went, and it fulfilled the “neutral projection target” social experiment perfectly. I heard quite the range of things referred to while pointing fingers at it, from the usual remarks about Congress and the presidency, to the Marvel Cinematic Universe, Disney, Game of Thrones, Star Wars continuations, game companies…. there are apparently many ongoing uncontained dumpster fires in society as we know it.

Some of them even move around and come to you.

You can see #YourWaifuIsTrash in action in this Dragon Con music video (skip to 8:15 if the time link doesn’t work!)

And finally, we make it to the Big Day at Robot Battles!

I’m a dope for not getting to it sooner – somebody had to point out to me that the dumpster was missing an UWU face (yes, it’s a face, not a sound…. today you learned?!), and so one was hastily appended with markers.

This thing managed to actually pull off a win. I did it by basically bull-baiting the opponent at the edge of the stage and letting nature take its course.

Of course, it couldn’t push anything, could barely get over the “arena” borders which are left beat-up on purpose, and had issues with turning in place under its own weight and the traction of the outdoor style carpet of the stage. So that was all! I also entered it in both rumbles at the end, but it got bowled over rather quickly in both rounds.  Nevertheless, I consider #YourWaifuIsTrash a win, because what is a win in #PostmodernRobotics? It’s whatever you want it to be!

This thing came back from Dragon Con working just fine, so it will live on as a stupid prop for all of eternity. I’ll probably repaint (read: just spray over it AGAIN in more shitty spraypaint!) it soon and begin adding choice tasteful decals.

Do you want your own? The CAD files in STEP, IGES, and Parasolid are available on the References page!

The Long, Cold Winter of No Posting Ends: Awaken the sadbot2019

Apr 16, 2019 in Bots, Overhaul 2, sadbot2016

Is this thing still running?

Needless to say I am a little less than proud of the longest post drought this site has ever seen. I’m still alive! Just preoccupied largely with getting the company product technology to a stage where I can at least be assured the tunnel will end eventually, even if I haven’t seen the light yet. Along with this gradual better-scoping of product tasks, it’s taken me a while to get used to not just working on dumb projects all the time in big blocks of work, but learning how to divide up tasks and think about their dependencies more, such that I can pick stuff up and drop it back off easily. I brought this up a bit in the preamble of the Great Mikuvan Engine Rebuild Scandal of yesteryear. Whatever, it just means hopefully I can get back to working on stuff, but until the day I exit the company and become a full time bad idea investor, the pace will inevitably be slower.

I believe the real world calls this “Adulting”.

Anyhow, adulting is dumb and robots are cool. Let’s revisit Sadbot, which was left kind of functioning last year some time before I sold the pokey dingle to a west coast team. Then, incrementally more parts started coming out of it until there wasn’t much left but Overhaul 1′s drive system and a steel box. With the coming of BattleBots season 4, I figured I had to at least work on something, and I should probably consider repairing my wreckage instead of creating new wreckage.

Oh, if you notice the timing of this post – I’m clearly not competing in Season 4 with Overhaul.


I mean, if I didn’t even clean the barbeque out of it yet….

Ultimately I didn’t think I could muster up the time and resources to do the bot justice, and enough of the team has split off to get real jobs (among other things, I mean) that i would have had to rally up a new crew. So, perhaps next year, and maybe it’s a blessing in disguise because now I’ll work on Sadbot out of FOMO and remorse, perhaps discovering something new about Overhaul in the mean time!

Next season, though. I promise I’ll be Bach.

So I set out to change up Sadbot in a fashion that would reflect the mods I want to make to Overhaul for next season. That in detail is itself an entire blog post for when Overhaul is modified for #Season5 one day, but in short…

  • Change the drivetrain to the 80mm “melon” motors – Sadbot being a single motor per side, it will 100% reflect the drivetrain setup I want Overhaul to have in the future, as in my post-season assessment the dual motor setup has not been as reliable as I wanted.
  • Using this opportunity to make sure the 12FET Brushless Rages weren’t actually trash, but were not utilized right the first time out. I had some more testing and changes I wanted to make after Season 3 that I hadn’t gotten around t
  • Finally doing the tractor pull contest between Sadbot and Overhaul which never happened. While the bot had “more” traction than Season 2, it wasn’t that much more, just more linear and predictable. I want more, something which I suspect is beyond the capabilities of my current bot architecture.

The first step is putting the damn thing together again. To do that, as usual, it has to come apart more first!

To retrofit the 80mm outrunners, I had to re-introduce Overhaul 1′s intermediate drive gear. The previous motors in Sadbot were 59mm SK3 outrunners running into Banebots P80 gearboxes, so the motors were already geared down and only needed the center sprocket.

To get the ratio I needed using a gearbox would have made the assembly too long to fit into the frame, so I needed to directly attach the motors to the face, needing the extra ~3:1 the intermediate gear provides.

I machined these gear-sprocket combos late last year. They’re waterjet-cut 12DP gears that are pinned into the sprocket face such that the assembly rotates on a dead shaft (pictured mounted in its former home). These were virtually identical to Overhaul 1′s (which were long disassembled or I’d have used them again!) but a different ratio.

New socket cap screw holes sunk into the drive plates – now featuring THREE bolt patterns! P80, 3″ Ampflow/Magmotor, and 80mm C-series outrunner.

Modules taken apart, cleaned, regreased/re-threadlocked, and reassembled.

At this point, the ‘skateboard’ of the bot weighed 163 pounds without batteries or the controller housing. This began my contemplation for bringing back the pokey dingle. I’d sold it because I didn’t like the design any more and someone else was going to incorporate it into another bot, so what better way to force me to start over?

Originally, Sadbot was going to be 220lb (nationwide Heavyweight class) without the pokey dingle, functioning only as a pusher/brick bot, and 250 pounds with it in order to simulate a BattleBots practice opponent. I was, after this weigh-in, now convinced I could make it close to 220lb even with a weapon, which would let it compete in the rising amount of “Heavyweight Sportsman’s” events around the country. Or at least I’d get it close enough that the laid-back nature of these events would make them take it anyway!

Next up, assembling the control deck. These were parts also designed and cut out last year – a basic polycarbonate tabbed box and nutstrips to make a second floor. Batteries will be mounted on the first level, and the aluminum plate mezzanine will house the brushless Ragebridges.

Originally, I wanted to use the Overhaul 1 batteries after being decomposed from the modules. However, they aged poorly and the cells have high internal resistance now, so I put together some of the Overhaul Season 3 batteries (Hobbyking Graphene bricks) instead. I greatly enjoyed how these worked in Overhaul, and while it packed four, I think two would have been plenty. Well, it’s time to test that!

The batteries are secured on the bottom with a few acres of Dual-Lock – think gender neutral Velcro for the woke Millennial – and then pressure-retained downwards by the 1/8″ aluminum plate with the adhesive-back foam rubber pad.

I forgot how easy wiring a 3-motor robot was. That’s it! This is the whole wiring harness, minus the battery-side mating connectors.

The rest of the wiring was built up over basically one evening. I had two leftover Whyachi Switches, one which I’ll set aside for the New Pokey Dingle weapon and the other for the drive. This keeps the activation process similar to what’s expected for BattleBots and also just allows me to test one system or the other.

And that’s all, really! This build was quite short and pleasant, occurring over several nights in about a week and some. Sadbot at this point weighed just under 180 pounds, which only left me around 40 for the entirety of the New Pokey Dingle. Difficult, and I decided at this point that the 220lb max goal was probably not that important, but I’ll give it a try.

 

I knew the parts I wanted to use already – an Overhaul lift gearbox (Banebots BB220 16:1 and SK3 59mm 149kv motor), enough reduction to get to about 180:1 which is the same ratio as Overhaul, and that the end effector should still be the Harbor Freight “manual slide log splitter” / toe destroyer. Furthermore, last time I permanently welded the tool to the output shaft, but this time I intended to make the output a socket to potentially make interchangeable ends.

I started flowing plates around some initial component placements. The output sprocket was only going to be able to get so big, so I fixed that first (48 tooth) and gave it a position that had some clearance to the electronics box, some clearance to the ground, but high enough to allow the motor to tuck underneath with some semblance of an intermediate stage. The width was fixed by choice at “Between the Melons” – one of the things I didn’t like about the last Pokey Dingle was how wide it was for what it did, and I had some ideas which involved moving the sprockets around to make the while thing narrower.

Here’s roughly what that looks like. The chain stages are very short and all overlap. Technically, I could have made this just open gearing, but chain drive is more available and serviceable – all of these sprockets, save for the output, are off the shelf parts.

I was contemplating how to make interchangeable “manipulator” sockets compact enough to fit in the confines of the side plates. I played with a couple of ideas including welded machined parts, making it a live shaft again (but with a socket tube welded to the shaft, and so on. All of these ideas turned out to be either too wide or, after a moment of …. brilliance? too tacky and complex.

Why not just weld the damn square tube to the plate sprocket, using the bushing as a locating feature!? The  wall thickness of the tube certainly permitted any inserted attachments to not come in contact with the drive chain, so that was really all.

I also utilized a chain tensioning approach which I remembered, but couldn’t place where I learned it from. Typically with a slotted mounting system you’d place the slots parallel to the direction of tension needed, e.g. slide the motor away from the shaft perpendicularly if you need to adjust the chain/belt spacing.

However, this arrangement doesn’t resist the normal forces that chain tension plus torque puts on the sprockets, which tends to force them together and loosen things up. At least, not all that well unless you had massive fasteners. Instead, I angled the bearing mounting slots at 30 degrees from the perpendicular to the axis joining the sprocket centers. This means I move the sprocket more “up and down” relative to the other one, but there’s that 0.5x component introduced by the 30 degree inclination which adjust the actual tension, and also reduces the effect of the tension “attractive force” immensely.

The downside? I have to have two chain pitches (well, sqrt(3) / 2, so basically 2) of vertical free movement in the chain to gain that horizontal spacing. That’s not all that much when considered, so only a little geometric squishing was needed to get space for everything.

Initial positioning in the bot  yielded some more Geometric Squishing to get the parts to all clear. I went out of my way to make things actually parametric and geometrically related instead of hard-coding dimensions, enabling some click-and-drag placement.

The final assembly by itself modeled with shaft and bearings for a realistic weight. It looks like this thing will weigh a little over 40 pounds after all. I added some cutouts to remove material where it wasn’t really needed, but the final bot will still end up around 225lb.

About a week later, this showed up! I sent these out to a local shop which the company has built up some rapport with, and they laser cut it from 1/4″ regular-ass P&O steel. Nothing too high tech going on here, though I recommended they stock up on ARx00 steel for future robot seasons…

Because I wasn’t in control of the machine any more, I very liberally oversized all the slots and shrunk the tabs – I went 0.015″ oversize in X and Y for planar square slots, principally. This turned out to be a near perfect, slightly jiggly fit. Laser cutting generally has a less clean finish than waterjetting, plus I couldn’t order them to “move the laser inwards 5 thou” like I typically fudge nozzle offset distances when waterjetting personally.

 

The machined parts needed for this new Pokey Dingle was really just the output dead shaft/epic standoff. I used some 1″ precision ground shaft leftovers and end-tapped both sides.

It was then used as a welding fixture. The P&O (pickled and oiled hot roll) steel was very clean from the get-go, not needing the intense sanding/brushing typical of A36/A514 hot roll or tubing products.  So it was literally just 10 minutes of MIG blasting here.

I modified the Harbor Freight Robot Tallywacker this time by cutting off the heavy punch weight at the back – it’s just a 2″ steel billet chunk. Previously I drilled a 1.25″ hole into it and welded it to the output shaft. This time, the 1.5″ main body section is more interesting, since it will be cross-drilled and bolted to the tube socket.

 

I then proceeded to get carried away.

It started out innocently enough wanting to paint the frame of the New Pokey Dingle my signature Overhaul Miku Blue – and then I discovered I had a Miku Magenta can I never used!

Yeah, well, this is what you’re getting now. aestheticbot9001

I was also tempted to paint the frame itself a light pastelly purple, but by this point didn’t want to disassemble the thing again.

Marking and drilling the front mounting holes for the NPD which brace the thing against the massive C channel section of the front of the bot. Another reason I didn’t like the old NPD – it only was bolted to the bottom of the the bot, meaning a hard enough hit and it will probably just bend. The New Pokey Dingle acts as a truss structure to past the center of the bottom plate – hopefully this will yield substantially more rigidity.

Drilling the holes themselves was an adventure. It was too heavy to put on a drill press, and too tall for the Bridgeport. So hand marking and drilling we go!

I’m rather fond of step drills. For hand drilling in steel, twist drills are almost inevitably too aggressive and tend to either spin in the drill or catch and throw you halfway across the room. Step drills feed more controllably and never dig and then slam the drill into your kidneys.

I machined a small donut piece to bridge the gap between the shaft bushing and the plate sprocket’s 2″ bore.

The same annular cutter I used for the original Pokey Dingle (as well as Overhaul’s gear holes and a lot of other parts) was used to put in the 1.25″ bushing hole. Really that was the only operation needed here! Just a single, albeit massive, cross hole.

Then you clean the parts and MIG-smash them together!

Here’s how it is going together. Since I don’t really care about the precise alignment of the socket tube, all the bushing has to do is center it. I put a few tack welds around that end first and more solidly welded the other side (carrying most of the load) – welding too much around these bushings would deform them due to the lower melting point of pressed-together bronze particles (not to mention sweat oil everywhere!)

Installation was simple, with just a few shim washers needed to space everything out.

Well, I ended up taking the whole bot apart again anyway, so maybe I should have painted the frame purple. But here’s how the New Pokey Dingle elevator machinery bolts in – a line of nuts on the bottom, and the four big bolts on the front.

I broke into the electronics enclosure again to add the 3rd Brushless Rage. I ran out of production-spec boards at this point, though, having packed the majority of them already for product shipment and BattleBots, so I pulled out one of the previous version power boards (The signal board is the same production-spec one though, just an older power end revision).

The 1″ UHMW top lid had to be modified a little to clear the new sprocket placement, which was a simple jigsaw job with drilled holes at the vertices to turn the saw around.

And here it is put together! The final weight? 226.5 pounds (with the top plate, which isn’t on here). I could probably knock 6 pounds out of it somewhere, but that’s not really the point.

So that’s where Sadbot sits now! It drives great withe dual 80mm “melon” drive, but I haven’t fought it against Overhaul yet or otherwise substantially battle-loaded it. In between the first photo and now, we actually moved shops again, and Sadbot is still hiding behind a few pallets. So, watch for both a post about the #NewVapeShop(tm) as well as some more testing and driving videos.

Dragon Con 2018: Postmodern Robotics Comes Home With a Vengeance

Nov 08, 2018 in Bots, Dragon Con, Roll Cake

Coming hot off my end-of-July trip to the mountain range I keep seeing next to I-81, and aiming to complete my original intended run down to Atlanta via the Blue Ridge Parkway, I decided to do Dragon Con a little differently this year.

Normally I’d be transporting down a whole production of robots from everybody and myself. Life, it seems, hits everyone eventually in the most inconvenient of ways, and a lot of my usual crew couldn’t make it (it seems startups are the robots and elaborate cosplays du jour).  And so this time, I decided early on to stop any plans for developing the next Überclocker /30-haul during the 3 or so weeks of August I had, and only bring Overhaul for display and what of Roll Cake I could get together. I wouldn’t even pack a Markforged printer this time! Imagine that.

So really this was one of the lightest loadouts I’ve done for Dragon Con, ever.  This was actually going to be different for me, and I wasn’t quite sure how to feel about it: Taking an eternity to get down there, actually maybe doing con stuff for once, and only whipping out a robot when convenient. Who the hell would ever do THAT? Go to an entire 100,000+ attendance convention to do stuff that’s not build robots!?

I did a speed-run departing Monday night before the con (Now featuring actual speed!) down to the area of Fancy Gap, VA where, the next day, I jumped onto the Blue Ridge Parkway. I was more interested in the mountainous portions in North Carolina, more so than the scenery itself, so I elected to skip the portion in Virginia as well as not run the Skyline Drive park again. There were plenty of opportunities to take Vans Next to Nature photos.

This was somewhere in Western North Carolina. Where? Hell if I know. The group of motorcyclists in this same parking area didn’t seem to know either. It seems you’re not supposed to know, or pay attention, or care at all; just disappear into the woods and assume you’ll pop out the other side at some point.

I get it. Not as much as someone who actually likes Naturing would, but I do understand.

As night descended on Tuesday, I decided to call a stopping point in Little Swaziland Switzerland, a mountain resort town. This region is very popular with motorcycle tours, as can be seen with Mikuvan’s new and temporary friends here. When you need the size of a van with the cargo capacity of a motorcycle…. Polaris Slingshot. By the way, the NC222A loop around this area is absolutely fantastic. I’m sure it gets tiring if you have to drive it every day to go to work.

I lied. While I didn’t bring along a Markforged printer, I sure as hell did bring a printer in general! I grabbed my “derpy van of 3D printers” Flashforge to make some parts for…. something, on the way down. Yes, I ran it overnight in a hotel room. I ended up having to build a pillow fort around it so I could actually sleep.

By mid-afternoon Wednesday, I’d reached the outer limits of Asheville and….. decided to tap out.

Keep in mind the Blue Ridge Parkway are all very winding, slow 2-lane roads, and that’s no way to cover distance effectively. At some point, I actually had to reach Atlanta and check into my AirCNC.

I decided to express the rest of the way after a harrowing foot-to-the-floor 55mph 4000RPM, 3rd gear climb up the side of Mount Mitchell for what felt like 10 minutes straight. If there was one moment that I was going to blow up my freshly rebuilt engine, I felt like it was going to be right there, but it would have been worth it. Worse, I was low on fuel at that point – there are no gas stations on the BRP – and feared that the straight uphill pull was going to get cut short. I basically coasted down the rest of the way into Asheville to try and conserve fuel.

From Asheville, I took I-40 west until US-74, then followed that down to US-23 – a well known historical path of mine, which I followed to basically outside my old front door…..

 

…step? Nah, in the intervening year, my parents sold the house. I instinctively glided into my favorite gas station from throughout high school and visits during my years at MIT, on Exit 111 on I-85, but realized I had no more business there afterwards. That was a strange moment indeed.

So, onwards we go to my aircnc house in downtown Atlanta. My local chariot was awaiting as soon as I got there! How positively quaint. There’s been a ton of fuss around Atlanta about scooter rentals lately. I mean, my whole goal of getting a place this close to the convention – right over the Downtown Connector in the “Most Boston part of Atlanta”, the Old Fourth Ward, was so I could just (as we memed it) “Millennial my way over” – whether that means rideshare app or silly scooter rental.

To be entirely based: I completely support silly scooter rentals. The only reason, in my mind, that they don’t work is because governments have outdated patchworks of laws regarding vehicular traffic that isn’t private passenger cars – our current society arguably came of age with the expansion of suburbs centered around the private car, and legislation has ossified around this concept to the point of being cancerous, just like infrastructure spending that is continually strongly biased towards private passenger car use. Much of the battle over scooter rentals is what kind of vehicle to tax, title, insure, and operate them as, and the context of legislative preference for FMVSS-certified normal people cars is unavoidable.

Fight me – I own several shitty cars and several more shitty scooters.

It would also help if people didn’t throw them in rivers.

 

Hi. (灬♥ω♥灬)

Who I think were the owners of this Model 3 were watching me very intently from a restaurant outdoor seat, so I didn’t get any closer. I was otherwise going to get within an inch for this photo op.

Thursday Funday is over – onto the con!

Overhaul was going to live in the Robotics track room for the whole weekend, so I did that unloading Thursday night when everyone was getting in the area, so I had backup. It would be rolled out for the Battlebots-related panels and otherwise hidden under a tablecloth. It was part of the Battlebots watch party and the “How to Get on BattleBots” Q&A session.

So, how do you get on Battlebots? Well, hell if I know. It’s clear your robot doesn’t have to be good.

 

That night, I finished the last print at my AirCNC house (whose host said “Would the neighbors mind if I ran a 3D printer all night?” was the weirdest request he’d gotten). And what I’ve been printing all along were in fact parts for my Overhaul cosplay.

It’s a little known fact that Haru-chan, like all good characters, has a male analogue. We actually have a rough sketch of what I call “Haru-dude” made by Cynthia (Lushanarts) from after the rework of Haru-chan:

But he’s too hot for me to pull off, so I simply used it as a design guide and changed up a few things (and also making it more realistic to put together). The “Overhaul head scythe” would obviously not be happening for Dragon Con, but I’ll consider it for something in the future.

I basically modeled and printed the whole thing on the fly, literally during the trip down and on site. I brought a handful of things I figured would be helpful, such as Velcro straps and hot glue and the like. Most parts were not actually modified from the CAD models of Overhaul parts, but made from scratch to exaggerate certain features that would appear too small if I just printed wheel_hub_assy.iam.

3D printing: Replacing the time-honored artform of hand-crafting costume pieces with on-demand kitted disposable bullshit, as-a-service, just like every good millennial trend!

So here we are.

Oddly enough, I was once again behind the camera 99% of the time and only really got this one photo taken of me (credit to Aaron Fan). Oh well, it was the prototype anyway. I actually don’t know of any full-body photos at the moment.

Besides the wrist shanks, I got a gray utility vest and added button snaps to reflect the staggered bolt pattern on the frame rails. I made two “edgelord belt chains”, one out of actual number #40H roller chain from Sadbot’s pokey stick) and one with orange wire loom wrapped around it.

I also made some cartoony wheel sprockets (which are hijacked #80 sprocket models, because again, teeth that are realistic can’t be seen in real life) to clip onto my repurposed motorcycle boots which I used for “dude-Ruby”. I had a few different shades of blue going on, which I’d like to fix for a future more proper rendition.

 

Saturday night robots with a few more of the crew. A couple of AirBnB houses around the area definitely suffered some robot building shenanigans. This was primarily to finish the 30lber seen on the right, but also to work on beetleweights because Sunday SUNDAY SUNDAY is the Robot Microbattles!

Likewise, after I got done working on other peoples’ robots, I put the last few solder joints in on Roll Cake, then test drove it in the hallway (“Do you mind if I test robots indoors?”). It’s quick, but controllably so, and I was fairly comfortable handling it after a few minutes. I like this new drivetrain a whole lot – the slight lag and torque ceiling of the hub motors is completely gone. It’s almost too twitchy now, and I know for a fact the drive motor size can come down to the next smaller outrunner class and be fine – this will be on the docket for a revision.

Now, back to the post title. I said there was a lot of postmodernism in the robots this year. What do I mean by that as applied to robots?

Postmodernism, broadly speaking, encompasses schools of thought which criticize traditional rationality and notions of objectiveness, calling into question the nature of what we call objective truth. In its basest form it often revolves around the ironic deconstruction and decontextualization of something in a disseminable media format, whether it be visual, text, audio, etc.. In a postmodern reading of something, then, nothing is considered “sacred” or free from reproach, and ideas are stripped down to their essence, lampooned and prodded, and then promptly bolted to the front of your robot.

Stance Stance Revolution is an instantiation of postmodernism in robot fighting: from a vertical spinner foundation, the discs are rotated to lie at angles to create an entirely new robot concept. It simultaneously derives from yet rejects the notions of the traditional vertical disc spinner, and is a complete eyesore while doing so. It raises questions at once of why the epistemological fuck would you do that and huh, I never would have thought of that. That’s kind of cool. I guess.

i am the department head of the school of postmodern robotics. don’t question me.

In short, it seemed to me like more robots than usual this year were doing away with, or severely reinterpreting “being competitive”. For instance, this….

….is quite the expression of postmodern robotics. Elements from a proven topology – a 2WD vertical “eggbeater” style drum – are seen as the foundation, but it destroys all notions of being outwardly serious and competitive by the fully functional LED-lit rubber duck mounted to it.

The duck is a liability. It’s a target for opponents. It prevents any form of operating upside down or self-righting. It might fall off and end the match right then… because all the electronics were stuffed inside it.

But it is the central statement of the bot, at the end of the day. This is truly the beauty of Postmodern Robotics.

¯\_(ツ)_/¯

From another branch of Postmodern Robotics, this robot is simply a knife with wheels. Why? Fuck you. It’s a knife with wheels. Are you really going to argue?

 

Roll Cake after the battles were all done. It gave some damage, and took some damage. But most importantly, it moved! And spun! And flipped things, mostly itself!

Full Disclosure: I actually slept through half of MicroBattles. ggwp. I showed up in time to watch a few more matches and participate in two rumbles at the end. Overall, I’m content with how the bot handled itself in the arena. One of the drive motor pinions ended up letting go and I was down one drive side for much of the first rumble, but used the gyroscopic forces of the drum to hobble around and make a few more hits.

One thing I ended up discovering was that the flipper arm wasn’t aggressive enough, due to the more conservative linkage travels I designed in. If your flywheel doesn’t slow down much per use, it’s oversized for the load power. I can probably make the linkage fan out more and trade some more efficiency points for a higher travel.

I ended up not really having time to recharge the battery for the second rumble, so it was running out of power around the middle. Overall, not a very competitive outing, but it showed me the drivetrain idea was sound now and the weapon drive system is fairly flexible in terms of actual layout. I’ll design up another version which is more Roll Cake 3.1 than 4.0 with some changes, but in the back of my mind is also a flipper-focused (non-exposed drum/flywheel) version, more like Magneato of NERC 30lb Sportsmans which Überclocker has fought a few times.

Now, we move onto Monday and the full-size Robot Battles. Remember when I said something about bad ideas just being bolted to your robot? Well some times it’s not even with threaded hardware….

That’s…. an interesting approach. Why so many ducks? Well, why not!? Better yet, they’re all squeak toys. Whenever this robot landed off the stage, it usually let out a protracted squeal sound from one OR MORE! of the ducks deflating.

It was otherwise a nondescript 4-drill-drive pusher bot. Postmodernism!

This is a robot which solely used a pool noodle for a weapon.

Appropriately named “Eyesore”, a newbie team (yay!) with a love for fluorescent paint.

 

nice bite force

 

Now we’re getting extra weird here. What do the ladybug balloons do on this robot? Nothing in particular. Yes, it fought every match with them!

There were not one, but two mildly-modified Roombas (and Roomba clones, as seen above) with things appended to them. One was in fact still “autonomous”, as autonomous as a Roomba can be, and was simply set loose on the stage.

This is a….

You know what? This isn’t even postmodernism any more. An entry with a FULLY FUNCTIONAL, ALL 3D-PRINTED tower crane on top of it? Now you could say we’re hitting on the territory of…

poststructuralism.

Get it? It’s a crane. Structures. Hhhhueuheue

This little saw-bot returns from previous years with an overpowering serving of new incongruently-themed stickers.

(Saws on an open stage?! I always take the time to explain that all freely-spinning appendages of robots are limited to 20ft per second tip speed in the Robot Battles rules, in case the message doesn’t carry through on first glance).

And finally, the robot I was helping work on, Skuld! Built by Leanne from Valkyrie, it’s a 30lber that has a very competently-powerd hammer with a 63mm-class outrunner. This thing could hit hard if it needed! It also had brushless drive with some highly geared inrunners.

That’s not a safety cover on the hammer arm end. That is the hammer arm end: One of several interchangeable plushies.

r/PostmodernRoboticsInAction

 

This is what the ideal robot fight looks like. You may not like it, but this is peak performance.

I don’t even know what the snout-on-a-piece-of-wood is from, but it paired with a powerful drive base is surprisingly effective.

Look! I entered a robot this year! It’s only 217 pounds overweight, no biggie.

On a last minute whim before the 12lb 30lb rumbles, we decided to heave Overhaul on stage to act as an arena hazard (it’s not running since I haven’t repaired the ESC damage from #season3 yet). It added an interesting play element: Suddenly, there was something to drive around and play hide-and-seek behind. People used Overhaul immediately to their advantage this way, skulking around looking for easy openings. Bots with giant wheels could escape by just driving up and over the forks. At one point, 3 or 4 30lbers teamed up to try and push Overhaul – they got a few inches in before the party got violent and broke out into fighting.

Probably one of the best rumbles I’ve ever witnessed come out of this event. It really makes me want to add a terrain element to the MassDestruction arena even more, in order to change up the small-bot game.

And this concludes your introductory lecture to Postmodern Robotics! I took a while to meander back north afterwards. Overall, I can say this Dragon Con was way more stress-free than any previous one. I was happy to see the competitive edge coming off of Robot Battles again, because a few years ago, when I and Jamison and many others were in (or around) colleges, we went through what I call the Tryhard Era of Robot Battles where the matches were becoming just as intense as any of the NERC parties and newbies were getting shut out or demolished. With the return of the TV shows, a lot more folks are cutting their teeth (metaphotical, drum, or otherwise) at these events, and I’ll happily step aside (or sleep through) them to let the interesting unjaded, sacrilegious designs fluorish.

On deck for the immediate arrival of fall is a lot of company-related pregaming before winter really sets in, so I’ll probably have limited content again for a little while. I’ll be slowly picking at 30haul, Overhaul, and the silly van nation in the mean time, but probably aren’t going to do any intense building until well after the new year.

Roll Cake 3: The Build!

Oct 09, 2018 in Bots, Roll Cake

It’s time to put a robot together! This post covers the entire fabrication of Roll Cake 3 in the week or so before Dragon Con. The goal of the bot was primarily to try and drive better with an indirect drive brushless setup and also further refine the packaging and action of the flipper linkage. Will it do anything?! Hell if I know, that’s the fun part to discover!

Even as I was finishing up the design the weeks prior, I was pregaming getting parts. Basically as soon as I determined the C2028 motor would fit in the triangle behind the wheels, I went ahead and ordered 3 more since I only had 1 to start with.

I also ordered these OMG THE MOST ADORABLE LITTLE 0.8 MODULE PINIONS EVER THAT COST WAY TOO MUCH MONEY from SDP-SI. I had to go solely by what they sold for 2mm bores in these gears. I wanted an 8-tooth gear to achieve the 8:1 reduction I wanted to get with the wheel gears, but they only sold the 8-tooth with a 3mm bore. So my drivetrain reduction is going to end up more like 10.6:1, which is fine by me – the bot will be too fast no matter what.

The problem with these tiny gears? The 2mm bores were slip-fit, not press-fit! Certainly irritating, but not the end of the world. Already noted for a revision in the future is maybe transitioning to R/C model pinions, such as R/C car transmissions. Those typically come in 3mm or 1/8″ bores.

I used Loctite 609 to stuff the pinions onto the motors in the end – I tried to silver solder one of them to little success – while I’ve managed to solder or braze pinions before, it seems that the steel they used in this motor shaft is an unusually high chromium grade which didn’t want to take with any flux I had on hand.

That was before I melted the pinion completely. Ah well.

Completed drive motors refitted with their shafts, which was a minor press fit job. I also replaced the stock stainless steel prop-saver screws with drilled-out and re-tapped #4-40 set screws. Another minor point of trouble with these motors is that due to their length and the small shaft diameter, it was hard to get these things to spin entirely true again after resintalling the shaft. A shorter motor (more pancakey) will resolve this.

I put the gearbox parts on print in Onyx as soon as I finished the bot design. The two ring gears and main cam linkage (sticking off to the left) have hoops of carbon fiber; everything else just derives strength from a bunch of perimeters. On the very left are the two connecting links between the cam link and the arm. I also made two first-pass prints of the drive wheels, seen here with O-rings.

Frame parts freshly done and needing cleaning. I’d say this is the only irritating part of doing unibody bots for me – picking the support out of difficult crevices. There’s certainly orientations that I can print in for minimal support, but they sacrifice immense strength in the part itself.  Both of these frame halves were printed in the orientation shown to give continuous loops in the XY (flat) plane.

In Roll Cakes past, I’ve actually taken to making fiber laps around the frame in this orientation, but with the more recent-ish changes to Eiger, you can change the perimeter and fill with more flexibility such that I just stack on the perimeters.

Otherwise, pull out some injection-molded part design – relatively constant wall thickness and smooth transitions if you can manage it, using ribs and cavities versus just solid massive areas, etc. However, my habit with 3D printed frames is leaving a few bulky areas up front such that they remain somewhat hollow – this acts as a very effective energy absorbing medium. For instance, basically the front inch or so if this bot is solid in the model, which means it’s perimeter plus non-solid infill in real life.

 

Drive motor installed with some test fitting done on the wheels here. Most of the hardware on Roll Cake 3 is specified as plastic or metal threadforming screws. If you get really fancy, people like using heat-set or tanged flanged inserts in MarkForged prints. However, I like my expediency, so some fat #10 tri-lobe threads will do to hold the wheels on.

Here’s the final drive fitup. The 0.8 Mod (32-ish DP) gears printed perfectly fine. In my experience, this is about as small as you can print reliably because the nozzle diameter still is small enough to go in and out of tooth tips profiles.

 

Both sides now fitted with drives. The front binding screw is shown sticking out here.

…and now joined together. Already, this thing is way more rigid than last time side to side. Hell, I might as well just ditch the flipper and make it a pure drum :v

The screw length needed to do this assembly were compromises with what I had on hand, so the bot dimensions shifted a little to accommodate them. Roll Cake is in fact not a perfect circle, but slightly squished inwards to yield the rough double-D-flat shape.

I slid in the trigger piece (which has a cutout for the servo arm) first, then I slid the servo into the DMs.

Alrighty, all the easy 3D printed stuff is assembled now. I still have to make a drum and motor, so off to Taki-chan we go!

(Also, check out the waterjet-cut feeder wedges made from leftover Hardox 450 from Overhaul!)

First order of business: separate the motor magnet ring so I can stuff it inside the drum. This can’t always happen cleanly, depending on the motor’s construction. The Donkeys have a single-piece stamped steel rotor, so I simply chucked the shaft in and very carefully parted at the outside corner where the magnet ring area joins the endcap.

With a motor that has an aluminum endcap, it’s often scarier since the parts can separate and self-destruct.  Luckily, this operation went very smoothly with higher speed and gentler feed to keep the forces on the rotor low.

Next up is to rough the drum shape. Most of this was easy, but I had to make the dual-disk shape, so I had to cut a valley in the middle. I just went with multiple staggered parting tool cuts to nearly the right shape, then very very carefully and gently made really shallow passes side to side to clean the profile up. Very gentle. These insert tools really should not be taking any side forces. To do this without wallhacking, I’d have gotten a single wider custom-ground HSS tool or something.

 

Then I bored the drum interior. There’s three stepped diameters – one for the ring bearing, then the magnet ring of the motor, then the “doesn’t matter” internal diameter. For the output side “bearing-stem-gear” I just did a straight drill to 12.0mm since it did not have to be that precise.

Next up: stator holder.

With the aluminum parts roughed out, I decided to make the one odd piece, which is the gear-on-a-stick that will carry the drum energy into the gearbox. This was a pretty easy turning job, but remember, it’s also the other bearing of the whole drum. The center bore, then, had to be 1. a clearance, but not by much, and 2. very clean and precise.

I actually went out and bought a 8mm-plus-0.001″ …. yes, this exists in America…. reamer to make this bore. You read that correctly – it’s a 0.3159″ reamer.

The gear gets a cylindrical boss on both ends eventually. After I finished both sides, I actually had to take a wire brush on an angle grinder to it in order to deburr the gear tooth edges – there were many little burrs and swarf hanging on which would have prevented the gear mate from working.

Parts in the midst of preparation! The stator bore has been drilled and the stem gear keyed on the top surface seen.

Throwing it together for a quick test fit! Here’s where it’s clearly visible that the stem gear skewers the cam ring gear and the cam linkage.

The next task was to drill the tooth holes in the aluminum drum body. I no longer have my old indexing head that made guest appearances in many of my undergrad builds, since I donated it to MITERS years ago. So to make sure I’m able to place the teeth 180 degrees apart, I milled a very shallow flat, then rotated it to sit on that flat, then milled another one.

This ensured I can drill and tap both sides with relatively equal precision. The teeth are just 3/8″-16 alloy cap screws, so they thread right in.

After the drum body was fully fnished, I broached it for a 3mm key – the stem gear is shown here mated to it. The magnet ring pressed into position without much trouble.

Unfortunately, I didn’t have time to make a new set of cluster gears, so I had to take them out of Roll Cake 2. Sad, since I wanted to keep that bot fully operational if I could!

The thought has crossed my mind of hiring out a whole basket of little cluster gears to be made if I’m going to keep evolving this bot.

The catch with these compound planetary cluster-fuck gears is that they have to be assembled at specific angle, or phasing, since there’s a hard relationship between the number of gears and the relative tooth counts. I scratched alignment marks into them when I first put them together for Roll Cake 1, and still use them for reference.

The gray goop I have dripped all over the assembly is liquid bike chain wax. I’ve been avoiding using petroleum-based lubricants like common greases because I don’t want to risk damaging the nylon-based Onyx material from the solvent action. Grease would also add immensely to the no-load drag of the gearbox, which is already a lot happening for a weapon drive.

The planet carrier installs easily after the gears are properly phased in place. It looks from here that there’s a ton of stuff going on, but I guarantee you this is not the case :v

As I mentioned in the design post, this carrier now has its own bearing to support itself. This is a pretty odd (but still apparently some kind of standard) 8mm bore, 14mm OD bearing – very low profile.

The drum drops into place from the front. The service order of this thing is a little suboptimal – to service the drum, I have to disconnect it from the folding linkage, but the central pivot bolt doesn’t rise up out of the body’s central cavity…. so really I have to undo the bottom linkage anchor (those three screws in a row from the CAD model) first, then remove the arm hinge. At least I made sure to make it all serviceable with at most 2 tools this time!

After the drum and arm are mounted, it was time for electrical dressup.

Along with the feeder claws, I cut another insectweight top plate set out of this piece of 1/32″ blue spring steel shim. I bought like 10 feet of this shim some time during undergrad, and have slowly been generating robots out of it since. This thing made its first appearance all the way back in 2009 with Pop Quiz’s rebuild! I’m now on the very last 8-10″ of it after Roll Cake’s parts are accounted for!

For better or worse, picking the parts out of the mother material was one of the last things I did before absconding on  3-day long slow meander down to Atlanta for Dragon Con. On the way, I hit up the Blue Ridge Parkway, like I promised myself I’d do. I only brought Roll Cake and its suite of service tools and a box of parts I think I’d need (mostly electronics), and Overhaul for display. This Dragon Con was going to be a pretty clean show instead of scrambling to take care of a few robots – the reason for this is I was pretty much solo this time, as there was a lot of bad timing involved for the various startups and schemes my friends and I are all involved in.

So what’s better than finishing your bot in the airBnB room when you got into town? Not all that much. I pre-gamed some of the electronics wiring (like battery leads and the like) before I left, so installing the two drive ESCs (AfroESC 12A) and weapon ESC (Spider ZTW 40A with SimonK) was a quick affair. I was able to drive Roll Cake around on the floor to get a gauge for its handling – which is much, MUCH improved over the hub motor drive version.

It’s very quick, but much more maneuverably so than Roll Cake 2, which tended to twitch everywhere. I swear the twitching is better than it was! At least now I could predictably send the bot places, which is an improvement over before!

The flipper geartrain was very tight, though, because I hadn’t had the chance to run it fully in up until that point. It would take several minutes of just running the drum at maximum speed and also a while of keeping the linkage engaged to wear everything in.

Here’s Roll Cake 3 fully buttoned up!

And shown with the flipper linkage at full height. In the next episode, hopefully you’ll get to hear about what it did, if anything!

The Roll Cake that Won’t Die: Roll Cake 3.0

Oct 03, 2018 in Bots, Roll Cake

I still like to pretend that I build robots here on this website! So in preparation for the fall round of events I like to go to (Dragon Con, Franklin, and any MassDestructions we try to hold) I decided in August to try and keep making progress on my recent persistent itch – Roll Cake.

Roll Cake had never “done well” – really done much of anything – at a competition since my main focus each and every time is kind of getting the vision of the bot finally in physical form. Remember its origin story and how I’ve been meaning to build a kinetic flipper for years, but never quite gotten around to it. It’s a robot built around a vision of a exterior shape and layout I came up with more than a decade ago, so it’s almost suboptimal on purpose.

Roll Cake 1 was sort of the grand puking of the idea in which nothing really worked. Roll Cake 2 made the mechanism shine, but still had a deficient drive due to sacrificing drivability for space conservation. My goal with Roll Cake 3 was to improve its driveability while making the weapon much more aggressive; Roll Cake 2 had a rather light drum/flywheel being belt-driven by an undersized motor that frequently overheated or shed belts.

The story of Roll Cake 3 actually dates back to not long after the previous Franklin Institute event, to which I brought it in order to talk about Alternative Flippers with a few other builders – it didn’t compete.

After mulling life on the return trip, I began the design by throwing some parts at the version 2 frame CAD and seeing what stuck. The principal design goals for V3 were:

  1. Moving to indirect drive on the wheels – the direct drive, while workable, was obviously still not very controllable. I figured a very small motor could tuck in the wasted volume (there’s a lot of wasted volume on Roll Cake) behind the wheels and could get me a considerable reduction just with open spur gears alone.
  2. Moving, on the contrary, to DIRECT drive on the weapon. The little 22mm outrunner just wasn’t enough to drive the whole geartrain continuously while also spinning a weapon. I could, with the increased drum interior volume, actually have a beetle-class weapon (so, you know, if the flipper plan just falls off a quarry cliff and explodes, it will at least be just a spinner)
  3. And lastly, moving to a dead shaft instead of V2′s live weapon shaft. This was more or less driven by going to a hub motor weapon. I’ll talk more about the Implications of this design change a little further down.

I had a Turnigy  C2028 motor model already, so I used it as a modeling guide for the positioning of the motor. I placed a Stance Stance Revolution motor, a Multistar pancake outrunner, in as a placeholder for the drum motor, though I wasn’t keen on using it. A motor that was a little more primitive seemed a better fit for the weapon.

To explore the space, I ordered some of the cheapest, shittiest motors you could buy on Hobbyking in the 35 to 45mm size range:

I love Hobbyking for having the sheer gall to sell you a motor that doesn’t have bearings. The Donkey line has bronze bushings and is seemingly made precisely to be the parts-recycling minimum viable products they are. A lot of builders have used them as foundations for their own weapon drives, and so will I!

I miss making motors, so this will be a fun distraction too.

I ended up selecting the Donkey 3511 motor for its stator size, but more importantly, the 12mm stator bore. The blue and silver “DT700″ motor had a thicker stator that I liked, but sadly only had an 8mm bore.

Why the bigger bore? I said earlier I was intending to move to a dead shaft for this iteration. Roll Cake historically has been rather tenuously held together side to side, with relatively small cross sections of material in the center due to the need to fit the flipper linkage. Moving to a dead shaft design allows me to use the shaft as an additional structural member of sorts up front.

The downside is I’d have to make a stator hub that the shaft presses into, and to do that, the stator needs to have a larger hole in the middle. I was intending on keeping the 8mm steel shaft that Roll Cakes have used for time immemorial (as in, literally the same one from v1 and v2), so that meant the stator needed at minimum, say, a 10mm center hole.

I pulled my usual motor designing tricks of making a hub for the stator to mount on, upon which a tpye 68xx ring bearing fits over. I sized this for a 6806 bearing, which has a 30mm bore. It’s a design balance between clearing shaft and wires versus simply being overly large and heavier.

I next generated a rough drum weapon shape that’s hollowed out in the middle. All of the dimensions and spacings were adjustable at this point – the final weapon would be a different width entierly. This just gets me something to start throwing into the CAD model so I can do the fitment of the gearset.

The teeth are, in typical beetle fashion, some big countersunk alloy steel cap screws.

With an eye for weight, I made some parametric adjustable cuts into the drum to turn it into more of a ‘dual disc’ configuration not unlike Witch Doctor and Hypershock. The final drum weight is tuned by just making the cuts smaller or larger.

Next up was the magical Roll Cake gearbox. I made some design changes to make it up to 1/4″ narrower to make the weapon itself occupy more of the front width. The clutch ring now has a single tooth and no longer its own outer support bearing – instead, it simply has a smooth shoulder inside to gently ride on the planet carrier. The carrier itself will have a 8mm thin-section bearing bored into it instead. There will be some extra friction from the technically bearing-less clutch ring, but the much more OP drum should more than make up for it.  I also got rid of an equivalent support bearing on the offset cam ring and it now only has a single bearing also in the center.

To pass power from the drum into the gearbox via the now dead shaft, I had to do something rather unconventional. There is now a lot of stuff going on here, so bear with me….

The distal endcap of the drum (opposite the motor end) is bored out to 12mm and has a key broached in it. A stem gear with a 8mm clearance bore has a keyway milled in one end and is inserted into the drum endcap with a key. The gear’s stem is 12mm OD and passes through the 12mm support bearing of the offset cam ring, and both transmits rotational torque and supports impact loads from the drum.

There is no “bearing” inside the stem gear in the conventional sense – there is only reamed steel on polished hardened steel with some oil in between.  Hey, if there’s one thing I learned from begrudgingly rebuilding an engine, it’s that steel on steel with a bit of oil in between is how every car works. What could go wrong!?

I knew going in I was betting a lot on this… technically a fluid bearing, but whatever…. working out. The friction would be higher than a ball bearing by far, but I was going to bank on the length of engagement making up for it with a light pressure resulting from the contact area.

Anyways, the gear end of the stem gear interfaces with the existing split-planetary gearbox and makes the thing go up and down.

One of the biggest challenges of Roll Cake has always been where to put the battery. When you scale robots down, you inevitably hit a “component Planck Length” of sorts – essentially, at some scale of robotting, the parts stop getting usably smaller. For me, the prismatic battery has always been troublesome for packaging inside a wedge-shaped robot. I played around with several methods, such as this one placing the battery forward and vertical…

…and including the unpalatable approach of splitting the battery up into two smaller ones. I really didn’t want to deal with the extra wiring and now squeezing on space for other components.

But one night I had a moment of come-to-Plastic-Jesus clarity – perhaps it is a reasonable compromise (it is – there ain’t no Perhaps, I’m just stubborn) to ditch the notion that the flipper has to span the whole width of the bot. At this point in the bot’s evolution, I should be thinking in terms of what makes the design work and what it actually needs, versus still trying to stick to my vision of “robot go flap-flap”.

In mulling over the compromise for the arm design, I also included a mockup of the new wheels, which will have a spur gear included on them to mate with a pinion on the motor.  I ended up just rolling with the C2028 motor and ordered a few from Hobbyking. Optimal? Maybe not. Fits back there and in stock? Hell yeah!

I decided to keep the battery arrangement shown – where the battery is placed widthwise in the bot, leaving the left half or so open to be used for the flipper linkage. This suddenly freed up a WHOLE LOT of volume inside the bot, and it was honestly a relief.

Before I went further with that design, I actually backed up and basically started over on another thought in my head about the design. There’s technically nothing stating Roll Cake had to be round. In fact, V1 was not round. Having the corners back could result in the difference between fitting in the battery vertically versus not, so I tried generating a square (chamfered octagon, I suppose) version of the frame to see if that was profitable.

Admittedly I did get pretty far along here – I found a vertical cavity for the battery and even was able to make space for mounting the drum motor. There wasn’t really anything preventing me from going with this design.

What swung me back the other direction was actually the sheer amount of usable space opened by repositioning the battery in the round design. I did want a Roll Cake in which trying to injection-mold ESCs and hyraulic press wires inside wasn’t even going to be an issue. From there, with an ideally working bot, I would make space optimizations as needed.

Well that does it for me. I returned to the round design and began cutting out cavities for everything. There’s gratuitous volume now to put things, and almost makes me wonder if Roll Cake could be a little smaller. However, for now, the final diameter was driven by giving the most space to the drive wheels and batteries while retaining an acceptable arm width that didn’t reduce it to just a stick.

Adding internal boss features to support the drum hub and drive motors now. I also made a crossing retainer for the battery – it sits in a neat little cavity and is prevented from bouncing around by the low wall and the eventual top plate. The geometry for the trigger pin is also taking shape.

Inside the left half of the bot, I made more space-filling features to mount the trigger servo. The dimensions did require cutting a hole of sorts in the underside to clear the servo cable. I moved the servo up as far as I thought was reasonable while still keeping the trigger pin on a radial path into the clutch ring gear.

Smaller but important features are now rolled up including the integrated wheel pegs and the arm pivot. The wheel pegs were going to be a machined piece, but gradually became so short there was no point in machining a part and using a mechanical attachment method. Instead, just printing the peg would do!

Notice how the bottom of the peg has a flat on it – to counteract the messy nature of homogenous-material support lattices in 3D printing which never really prints bottom-sides cleanly, I just made the peg a D-flat to give a single flat surface for the support to finish and the part to build. The eccentricity potential of the wheel from the bearing being on an incomplete circle is going to be negligible; worst case I’ll stuff a shim into the gap.

I put the arm pivot at the very front tip of the bot to make the arm as long as possible in order to get free height at the flipping end. This constraint would drive the arm shape and the placement of the linkages.

I made a first approximation of the arm after that. It had to start out higher than the bot’s upper slope surface in order to clear the cam and ring gears, which is why there’s a mild kink in it. You can see the cam ring passing through the arm here – I used this as a guide to make a cut that was just barely enough to clear it.

From there, it was relatively easy to make the linkage by fixing the cam linkage centered in the bot and fixing the arm in the lowered position. The lower anchor is a simple pin joint I modeled on the backside of the center crossing span of the bot, so all I really needed to do is adjust lengths and the position of the pin joint on the arm itself.

I tuned the linkage lengths to give me in the end around 4″ of rise. The end driving constraint was not hitting the crossing span in the middle when extended, but also when folded, not closing more than about 60 included degrees (or 30 per side measured from the centered cam link as a baseline).

At that point, which is my mental cutoff for “sensible linkage”, the orthogonal loading force from pulling the linkage open is twice the actual opening force, and just gets worse as you collapse the linkage more.

(This, kids, is why your elaborate scissor lifts never work in 2.007…. wait until you take 2.12 and understand the Jacobian matrix)

 

Here is that “JUST BARELY” cut I talked about – when the cam’s coming up, there’s only a few thousands of an inch of clearance as the arm goes up.

In real life, as I found out, the slop in the system actually made it such that the cam lifting shoved the arm upwards, helping the linkage get started out of the folded position. Sci………ence?

As a matter of habit when designing the smaller bots, I began adding hardware to make things more realistic for weight. On a bot that’s tight in space selectively like Roll Cake, I also wanted a sense of where fastener heads were going to go. So it turns out McMaster actually has intricately-cut models of their shitty sheet metal screws for download. I didn’t even know shitty sheet metal screws were 3D modeled, really. Either way, it was handy to see how much fastener head you actually need to clear.

The arm and linkages also get their dose of “Real-ification” by the addition of shoulder screws and properly sized counterbores, thru-holes, and tapped holes.

The linkage length allowed me to finally add one feature that Roll Cakes Past have never ever had: a rear structural link. There was enough leftover space to put a crossing span in the back with a bolt to tie it together! This might be the most structurally sound Roll Cake yet.

Space was tight enough that I needed to put the bolt model in and make sure I could still tighten a nut. The length of the righthand cavity was adjusted a little bit to be just barely longer than the bolt, so I can, you know, actually install it.

The three holes in a row above the rear crossing span? It’s a removable piece, serviced from the rear of the bot, so I can install and uninstall the arm linkage.

It’s a little hard to see what’s going on here. This is a counterbored, hidden cross screw which holds the front half of the bot together. It’s installable from the outside by squishing it past the O-rings in the wheels. You’d otherwise barely know it’s there!

This might be a better view of where it goes. It is sunk about an inch into the right hand (here, left side) half of the bot before the thread diameter begins, in order to put that much plastic in compression first.

I moved onto making some kibbles and bits for the bot – here are two little feeder fangs to try and get under someone and make sure the drum gets first punch. They’ll be waterjet-cut from some kind of leftover steel.

We’re getting awfully close with the CAD now. I took care of some more last details, such as the tiny half-round ears for if the bot gets flipped over to prevent the drum from hitting the ground. While Roll Cake can obviously drive upside down, the double-sided flipper was deprecated post v1, so it still has an “up” side. Maybe one day I will try bringing the double-sided flipper back.

I then made wire passthroughs and filleted corners and broke edges. This is the now-complete “unibody” frame.

I took snapshots of the side cavities and traced them in order to generate conforming top plates. The hole locations were patterned where I could and kind of freelanced where I couldn’t, at a fixed distance from the nearest profile curve.

To actually make the bot, the monolithic model had to split into three pieces – the two halves, plus a drum axle retainer for the non-motor side. I generated cutting surfaces for this operation. The split is not linear, but has a jog in the middle to accommodate convenient locations to begin and end the frame profile.

The cover plates are modeled from the sketch drawings individually. I suppressed the monolithic body and  imported all of the cut pieces and properly constrained them in order to yield the multi-piece modeled frame.

So that does it for Roll Cake 3′s design. In the next episode, I have to actually build the damn thing!